PandaX

Executive summary of PandaX-20T - April 26, 2026

Sun, 13 Sep 2026 00:00:00 +0800

Download: Executive_Summary_PandaX_20T.pdf

Dark Matter Search Results from 1.54 Tonne·Year Exposure of PandaX-4T

Sun, 06 Sep 2026 00:00:00 +0800

DOI: https://doi.org/10.1103/PhysRevLett.134.011805

Get all files: opendata.tar.gz

PandaX-4T Concludes Staged Operation as PandaX Transitions to the 20T Phase

Fri, 04 Sep 2026 12:00:00 +0800

At 15:56 on April 17, 2026, the PandaX‑4T detector at the PandaX Dark‑Matter Laboratory, 2400 m underground at the Jinping site in Sichuan, ceased operation upon the completion of Run 11162 as scheduled.

Probing scalar-neutrino and scalar-dark-matter interactions with PandaX-4T

Mon, 01 Jun 2026 00:00:00 +0800

DOI: https://doi.org/10.1103/pn9y-g5k7

Get all files: open-data.tar.gz

Tsung-Dao Lee Institute Hosted the 2nd PandaX-xT International Open Meeting

Thu, 21 May 2026 14:30:00 +0800

From April 6 to 12, 2026, the 2nd PandaX-xT International Open Meeting was successfully held at the Tsung-Dao Lee Institute.official event page. This marked the second international open meeting organized by the PandaX Collaboration since 2025. The meeting attracted nearly one hundred researchers from the United States, the United Kingdom, France, Germany, Japan, Russia, the Czech Republic, Slovakia, Australia, mainland China, and Taiwan, China. The conference was jointly chaired by Prof. Yifei Niu from Shanghai Jiao Tong University, Prof. Jianglai Liu from the Tsung-Dao Lee Institute, Prof. Fedor Šimkovic from Comenius University, and Prof. Qing Lin from University of Science and Technology of China.

PandaX-4T Sets New Precision Benchmark for the Half-Life Measurement of Xenon-136 Double-Beta Decay

Thu, 07 May 2026 12:15:00 +0800

Whether neutrinos are Majorana particles—that is, whether neutrinos are their own antiparticles—remains one of the most fundamental open questions in particle physics. Scientists worldwide are searching deep underground for the extremely rare process known as neutrinoless double-beta decay (0νββ), which would provide a crucial test of the Majorana nature of neutrinos. To reliably identify 0νββ, however, it is first essential to precisely measure the spectral shape and half-life of the Standard Model-allowed two-neutrino double-beta decay process (2νββ).

PandaX Collaboration Secures NSFC-CJPL International Collaborative Grant for Solar Neutrino Research

Tue, 16 Dec 2025 23:00:00 +0800

The PandaX Collaboration has been awarded an NSFC-funded international collaborative research grant for a project titled “Development of Key Techniques for Solar Neutrino Measurements with a Deep Underground Xenon Detector.” This project aims to advance neutrino physics by utilizing the facilities at the China Jinping Underground Laboratory (CJPL), the world’s deepest underground laboratory.

The project’s main objective is to develop a high-sensitivity xenon-based detector to study solar neutrinos, particularly pp neutrinos and ⁸B neutrinos. The research focuses on addressing key challenges, including reducing detector background noise, mitigating environmental and instrumental interference, and improving the detection and understanding of low-energy neutrino signals.

PandaX-4T: Search for Light Dark Matter with 259-day data

Tue, 30 Sep 2025 00:00:00 +0800

DOI: https://doi.org/10.1103/rtnh-jn8s

Measurement of solar pp neutrino flux with PandaX-4T commissioning run data

Tue, 27 May 2025 00:00:00 +0800

TDLI hosted an international Open Meeting for the PandaX-xT

Thu, 01 May 2025 01:30:00 +0800

Tsung-Dao Lee Institute hosted an international Open Meeting for the PandaX-xT project from April 7-11, 2025. PandaX (Particle and Astrophysical Xenon project, https://pandax.sjtu.edu.cn/), operating at the China Jinping Underground Laboratory (CJPL), utilizes staged xenon detectors to probe dark matter particles and investigate neutrino properties. The current stage experiment, PandaX-4T, has been operational since 2021. Meanwhile, the collaboration is developing its next-phase facility - PandaX-xT. This multi-ten-tonne liquid xenon observatory aims to achieve ultra-low background levels for multidisciplinary research. With approximately 40-tonne active xenon target, the full-scale PandaX-xT will explore new frontiers in dark matter detection, Majorana neutrino studies, astrophysical neutrino observations, and other ultra-rare particle interactions.

The week started with a three-day theory/phenomenology workshop at TDLI. During the subsequent two-day Open Meeting, the PandaX collaboration outlined the phased implementation plan for PandaX-xT, as well as design details and readiness of individual components of the experiment. Approximately 20 international experts shared perspectives on both scientific opportunities and technical challenges during the five-day program.

PandaX-xT—A deep underground multi-ten-tonne liquid xenon observatory

Fri, 22 Nov 2024 00:00:00 +0800

We propose a major upgrade to the existing PandaX-4T experiment at the China Jinping Underground Laboratory. The new experiment, PandaX-xT, will be a multi-ten-tonne liquid xenon, ultra-low background, and general-purpose observatory. The full-scaled PandaX-xT contains a 43-t liquid xenon active target. Such an experiment will significantly advance our fundamental understanding of particle physics and astrophysics. The sensitivity of dark matter direct detection will be improved by nearly two orders of magnitude compared to the current best limits, approaching the so-called “neutrino floor” for a dark matter mass above 10 GeV/c², providing a key test to the Weakly Interacting Massive Particle paradigm. By searching for the neutrinoless double beta decay of ¹³⁶Xe isotope in the detector, the effective Majorana neutrino mass can be measured to a 10–41 meV/c² sensitivity, providing a key test to the Dirac/Majorana nature of neutrinos. Astrophysical neutrinos and other ultra-rare interactions can also be measured and searched for with an unprecedented background level, opening up new windows of discovery. Depending on the findings, PandaX-xT will seek the next stage upgrade utilizing isotopic separation of natural xenon.

First Indication of Solar 8^B Neutrinos through Coherent Elastic Neutrino-Nucleus Scattering in PandaX-4T

Thu, 07 Nov 2024 00:00:00 +0800

The PandaX-4T liquid xenon detector at the China Jinping Underground Laboratory is used to measure the solar ⁸B neutrino flux by detecting neutrinos through coherent scattering with xenon nuclei. Data samples requiring the coincidence of scintillation and ionization signals (paired), as well as unpaired ionization-only signals (US2), are selected with energy threshold of approximately 1.1 keV (0.33 keV) nuclear recoil energy. Combining the commissioning run and the first science run of PandaX-4T, a total exposure of 1.20 and 1.04 tonne·year are collected for the paired and US2, respectively. After unblinding, 3 and 332 events are observed with an expectation of 2.8±0.5 and 251±32 background events, for the paired and US2 data, respectively. A combined analysis yields a best-fit ⁸B neutrino signal of 3.5 (75) events from the paired (US2) data sample, with ∼37% uncertainty, and the background-only hypothesis is disfavored at 2.64σ significance. This gives a solar ⁸B neutrino flux of (8.4±3.1)×10⁶ cm^-2 s^-1, consistent with the standard solar model prediction. It is also the first indication of solar B8 neutrino “fog” in a dark matter direct detection experiment.

Search for Low-mass Dark Matter and Solar Neutrino Using PandaX-4t Detector

Mon, 23 Sep 2024 00:00:00 +0800

First Indication of Solar ${}^{8}\mathrm{B}$ Neutrinos through Coherent Elastic Neutrino-Nucleus Scattering in PandaX-4T

Sun, 15 Sep 2024 20:45:00 +0800

Under the 2400-meter overburden of the China Jinping Underground Laboratory (CJPL), the PandaX-4T experiment has, for the first time, found indication of Coherent Elastic Neutrino-Nucleus Scattering (CE$\nu$NS) events induced by solar neutrinos. The finding, with a statistical significance of 2.64$\sigma$, is detailed in a paper titled “First Indication of Solar ${}^{8}\mathrm{B}$ Neutrinos Through Coherent Elastic Neutrino-Nucleus Scattering in PandaX-4T”. The paper was accepted for publication by Physical Review Letters on Sep. 11.

The historical journey leading to this finding is captivating. Neutrinos are elusive subatomic particles that provide key insights into the composition and force of nature, as well as the inner workings of stars. In 1973, the Gargamelle bubble chamber at CERN, Switzerland, unveiled a new type of weak force felt by neutrinos, known as the “neutral current”. The following year, Freedman theorized that when a low-energy neutrino (with wavelength comparable to or greater than the size of the nucleus) interacts with a nucleus, the neutral current amplitudes on individual nucleons are coherently added up, significantly boosting the probability of the scattering. This unique process, akin to x-ray diffraction on a crystal lattice but involving neutrinos colliding with nuclei, was later coined as the CE$\nu$NS. In 1983, the force carrier responsible for the neutral current, the Z boson, was unearthed at CERN (1984 Nobel Prize). Soon after this triumph, a proposal was made by Drukier and Stodolsky for detecting low-energy neutrinos through CE$\nu$NS, which requires ultra-sensitive detectors capable of sensing the minute energy carried by the recoiling nuclei. By 1985, Goodman and Witten recognized that such detectors were also well-suited for searching for the collisions between dark matter particles and nuclei. This sparked a four-decade-long global race of underground dark matter direct detection experiments. However, it was the detection of CE$\nu$NS that beat the crowd - in 2017, CE$\nu$NS was first observed using neutrinos produced from a proton beam at Oak Ridge National Laboratory in the US. On the other hand, despite enormous progress in the sensitivity of dark matter experiments, no definitive signals of dark matter particles have been found. It has been long anticipated that these underground dark matter detectors would eventually detect the CE$\nu$NS events induced by the solar and atmospheric neutrinos, which closely resemble dark matter signals, placing a “soft floor” on dark matter searches. By then, dark matter detectors also become versatile low-energy neutrino observatories, capable of exploring neutrino interactions and astrophysics through a novel approach.

The fusion reactions in the Sun release an immense number of neutrinos. The “hotter” end of the neutrino spectrum is dominated by those produced by the decay of boron-8 (${}^{8}\mathrm{B}$). These ${}^{8}\mathrm{B}$ neutrinos pass through the Earth in vast quantities—millions through a single fingernail every second. The first real-time observation of ${}^{8}\mathrm{B}$ neutrinos was made using a 2000-ton Kamiokande-II water detector in Japan in 1989, through neutrino-electron scatterings. Around the turn of the last century, precise measurements of ${}^{8}\mathrm{B}$ neutrinos were made using a 1000-ton heavy-water SNO detector in Canada, and an even larger 50-kiloton Super-Kamiokande detector in Japan. These measurements unveiled a peculiar fact: neutrinos possess tiny but non-zero masses, allowing them to ‘oscillate’ from one type to another (Nobel Prize 2015). However, apart from those at Oak Ridge, no other neutrino detections have been made by CE$\nu$NS. Such measurements are particularly challenging for astrophysical neutrinos such as ${}^{8}\mathrm{B}$ neutrinos due to the significantly lower energy signals (less than 1 keV).

The PandaX-4T detector is a dual-phase xenon time projection chamber with a sensitive mass of 3.7 tonnes, located deep underground in the B2 Hall of the upgraded phase of CJPL. Designed to search for dark matter and study neutrino properties, the PandaX-4T cutting-edge features—such as a low energy threshold, low background levels, and a multi-ton xenon target—provide excellent sensitivity to both dark matter and CE$\nu$NS signals.

With the data collected during the first commissioning run with 95 calendar days (Run0) and the first scientific run with 164 calendar days (Run1), the PandaX-4T collaboration has produced two world leading exclusion constraints on the interaction between dark matter and nucleons in 2021 and 2024. In this study, with combined data in Run0 and Run1, the PandaX team optimized the selection criteria for the CE$\nu$NS signals. The data were sorted into “paired data” where for each event both the scintillation and ionization signals of the energy deposition are recorded, and “ionization-only data” where an isolated ionization signal is recorded. The latter data set features an ultra-low energy threshold of about 0.33 keV, which greatly enhances the efficiency to ${}^{8}\mathrm{B}$ CE$\nu$NS events. The final fit of the data reveals an event excess above the background, with the characteristics matching the ${}^{8}\mathrm{B}$ CE$\nu$NS signal. In approximately 1 tonne-year exposure, the best-fit value for the ${}^{8}\mathrm{B}$ signal is 78.5 events (including 3.5 paired events and 75 ionization-only events). The statistical significance of the excess is 2.64$\sigma$, that is, there is only a 0.4% probability that the excess is due to random background fluctuations. The measured solar ${}^{8}\mathrm{B}$ neutrino flux aligns with the predictions of the solar fusion models. This result represents the first indication of CEνNS signals from a natural neutrino source. It also demonstrates that PandaX-4T has achieved a milestone sensitivity to dark matter.

Simultaneously, another liquid xenon experiment in Italy, XENONnT, is also actively engaged in this endeavor. Both PandaX and XENONnT presented their preliminary findings on CE$\nu$NS at the Identification of Dark Matter Conference 2024 in Italy, with PandaX presenting on July 8 and XENONnT on July 10. The PandaX paper was submitted to the preprint (arXiv) and Physical Review Letters on July 15, and received official acceptance from the journal on Sep. 11. XENONnT collaboration’s paper appeared on arXiv on Aug. 6, with a CE$\nu$NS significance of 2.7$\sigma$. The community is excited about these new findings - they came at the right time with the right characteristics of CE$\nu$NS. Future data from these xenon-based experiments are expected to advance the detection of CE$\nu$NS events towards precise measurements, opening up new opportunities in neutrino research and multi-messenger astronomy.

The PandaX project is led by Shanghai Jiao Tong University. Collaborating institutes include University of Science and Technology of China, Sun Yat-sen University, Shandong University, Peking University, Beihang University, Nankai University, Fudan University, Chengdu University of Technology, Yalong River Hydropower Development Company, and University of Maryland, with over 90 researchers. The PandaX project is supported in part by National Science Foundation of China, the Ministry of Science and Technology of China, and by Shanghai Municipal Government and Sichuan Provincial Government. The CJPL administration and the Yalong River Hydropower Development Company Ltd. have provided indispensable support. The PandaX project has also received important support from various foundations, including the Hongwen Foundation, New Cornerstone Science Foundation, Tencent Foundation in China, and Yangyang Development Fund.

Figure 1: The interior of the ultrapure water tank (passive shielding), revealing the outer vessel of the PandaX-4T cryostat.

Search for cosmic-ray boosted sub-MeV dark matter-electron scatterings in PandaX-4T

Thu, 05 Sep 2024 00:00:00 +0800

We report the first search for the elastic scatterings between cosmic-ray boosted sub-MeV dark matter (DM) and electrons in the PandaX-4T liquid xenon experiment. Sub-MeV DM particles can be accelerated by scattering with electrons in the cosmic rays and produce detectable electron recoil signals in the detector. Using the commissioning data from PandaX-4T of 0.63 tonne·year exposure, we set new constraints on DM-electron scattering cross sections for DM masses ranging from 10 eV/c² to 3 keV/c².

Signal response model in PandaX-4T

Fri, 19 Jul 2024 00:00:00 +0800

PandaX-4T experiment is a deep-underground dark matter direct search experiment that employs a dual-phase time projection chamber with a sensitive volume containing 3.7 tonne of liquid xenon. The detector of PandaX-4T is capable of simultaneously collecting the primary scintillation and ionization signals, utilizing their ratio to discriminate dark matter signals from background sources such as gamma rays and beta particles. The signal response model plays a crucial role in interpreting the data obtained by PandaX-4T. It describes the conversion from the deposited energy by dark matter interactions to the detectable signals within the detector. The signal response model is utilized in various PandaX-4T results. This work provides a comprehensive description of the procedures involved in constructing and parameter-fitting the signal response model for the energy range of approximately 1 keV to 25 keV for electronic recoils and 6 keV to 90 keV for nuclear recoils. It also covers the signal reconstruction, selection, and correction methods, which are crucial components integrated into the signal response model.

Radon removal commissioning of the PandaX-4T cryogenic distillation system

Mon, 08 Jul 2024 00:00:00 +0800

The PandaX-4T distillation system, designed for the removal of krypton and radon from xenon, is evaluated for its radon removal efficiency using a ²²²Rn source during the online distillation process. The PandaX-4T dark matter detector is employed to monitor the temporal evolution of radon activity. To determine the radon reduction factor, the experimental data of radon atoms introduced into and bypassed the distillation system is compared. The results indicate that the PandaX-4T distillation system achieves a radon reduction factor exceeding 190 at the flow rate of 10 slpm and the reflux ratio of 1.44. Gas-only online distillation process of a flow rate of 20 slpm is also conducted without observing significant reduction of radon levels in the detector. This observation suggests that the migration flow of radon atoms from the liquid phase to the gas phase is limited, and the flow rate of gas circulation and duration of the process are insignificant compared to the total xenon mass of 5.6 tons in the detector. This study provides the experimental data to support the efficient removal of radon at ∼Bq level using the PandaX-4T distillation system, which is the prerequisite of the radon background control in the detector. The further operation with higher flow rate will be applied for the upcoming science run in PandaX-4T.

Search for solar pp neutrinos using PandaX-4T electron recoil data

Sat, 15 Jun 2024 00:00:00 +0800

The proton-proton (pp) fusion chain dominates the neutrino production in the Sun. The uncertainty of the predicted pp neutrino flux is at the sub-percent level, whereas that of the best measurement is O(10%). In this study, for the first time, we measure solar pp neutrinos in the electron recoil energy range from 24 to 144 keV using the PandaX-4T commissioning data with 0.63 tonne × year exposure. The pp neutrino flux is determined as (8.0 ± 3.9 (stat) ± 10.0 (syst)) × 10¹⁰ s^-1 cm^-2 , which is consistent with the Standard Solar Model and existing measurements, corresponding to an upper flux limit of 23.3×10¹⁰ s^-1cm^-2 at 90% C.L..

Data reduction strategy in the PandaX-4T experiment

Mon, 13 May 2024 00:00:00 +0800

The PandaX-4T experiment is designed for multiple purposes, including searches for solar neutrinos, weakly interacting massive particles, and rare double beta decays of xenon isotopes. The experiment produces a huge amount of raw data that needs to be stored for related physical analyses in a wide energy range. With the upgrading of the PandaX-4T experiment, the doubled sampling rate resulted in a larger data size, which challenges both the cost and the data processing speed. To address this issue, we propose a data reduction strategy by removing the noise tail of large signals and downsampling the remaining parts of them. This strategy reduces the requirement for storage by 65% while increasing data processing speed. The influences on physical analyses on different topics at different energy regions are negligible.

Improvement on the linearity response of PandaX-4T with new photomultiplier tubes bases

Fri, 10 May 2024 00:00:00 +0800

With the expanding reach of physics, xenon-based detectors such as PandaX-4T in the China Jinping Underground Laboratory aim to cover an energy range from sub-keV to multi-MeV. A linear response of the photomultiplier tubes (PMTs) is required for both scintillation and electroluminescence signals. Through a dedicated bench test, we investigated the cause of the non-linear response in the Hamamatsu R11410-23 PMTs used in PandaX-4T. The saturation and suppression of the PMT waveform observed during the commissioning of PandaX-4T were caused by the high-voltage divider base. The bench test data validated the de-saturation algorithm used in the PandaX-4T data analysis. We also confirmed the improvement in linearity of a new PMT base design with three more low radioactivity capacitors at later dynodes, which will be used to upgrade the PMT readout system in PandaX-4T.

Detecting Neutrinos from Supernova Bursts in PandaX-4T

Wed, 17 Apr 2024 00:00:00 +0800

Neutrinos from core-collapse supernovae are essential for understanding neutrino physics and stellar evolution. Dual-phase xenon dark matter detectors can be used to track explosions of galactic supernovae by detecting neutrinos through coherent elastic neutrino-nucleus scatterings. In this study, a variation of progenitor masses and explosion models are assumed to predict neutrino fluxes and spectra, which result in the number of expected neutrino events ranging from 6.6 to 13.7 at a distance of 10 kpc over a 10-s duration with negligible backgrounds at PandaX-4T. Two specialized triggering alarms for monitoring supernova burst neutrinos are built. The efficiency of detecting supernova explosions at various distances in the Milky Way is estimated. These alarms will be implemented in the real-time supernova monitoring system at PandaX-4T in the near future, which will provide supernova early warnings for the astronomical community.

Waveform simulation in PandaX-4T

Wed, 27 Mar 2024 00:00:00 +0800

Signal reconstruction through software processing is a crucial component of the background and signal models in the PandaX-4T experiment, which is a multi-tonne dark matter direct search experiment. The accuracy of signal reconstruction is influenced by various detector artifacts, including noise, dark count of photomultiplier, photoionization of impurities in the detector, and other relevant considerations. In this study, we presented a detailed description of a semi-data-driven approach designed to simulate a signal waveform. This work provides a reliable model for the efficiency and bias of the signal reconstruction in the data analysis of PandaX-4T. By comparing critical variables that relate to the temporal shape and hit pattern of the signals, we found good agreement between the simulation and data.

PandaX-4T: Run0 S2 Only

Sun, 17 Sep 2023 00:00:00 +0800

S2 only data release: s2only_data_release.zip

Search for Light Dark Matter with Ionization Signals in the PandaX-4T Experiment

Tue, 27 Jun 2023 00:00:00 +0800

We report the search results of light dark matter through its interactions with shell electrons and nuclei, using the commissioning data from the PandaX-4T liquid xenon detector. Low energy events are selected to have an ionization-only signal between 60 to 200 photoelectrons, corresponding to a mean nuclear recoil energy from 0.77 to 2.54 $keV$ and electronic recoil energy from 0.07 to 0.23 $keV$. With an effective exposure of 0.55 tonne · year, we set the most stringent limits within a mass range from 40 $MeV/c^2$ to 10 $GeV/c^2$ for pointlike dark matter-electron interaction, 100 $MeV/c^2$ to 10 $GeV/c^2$ for dark matter-electron interaction via a light mediator, and 3.2 to 4 $GeV/c^2$ for dark matter-nucleon spin-independent interaction. For DM interaction with electrons, our limits are closing in on the parameter space predicted by the freeze-in and freeze-out mechanisms in the early Universe.

Study of Accidental Coincidence Background in the PandaX Experiment and Search for 8B Solar Neutrino

Thu, 01 Jun 2023 00:00:00 +0800

Limits on the luminance of dark matter from xenon recoil data

Thu, 18 May 2023 00:00:00 +0800

It is commonly conjectured that dark matter is a charge neutral fundamental particle. However, it may still have minute photon-mediated interactions through millicharge or higher-order multipole interactions, resulting from new physics at a high energy scale. Here we report a direct search for effective electromagnetic interactions between dark matter and xenon nuclei that produce a recoil of the latter from the PandaX-4T xenon-based detector. Using this technique, the first constraint on the charge radius of dark matter is derived with the lowest excluded value of $1.9 \times 10^{-10} fm^{2}$ for a dark matter mass of 40 giga electron volts per speed of light in a vaccum ($GeV / c^{2}$) more stringent than that for neutrinos by four orders of magnitude. Constraints on the magnitudes of millicharge, magnetic dipole moment, electric dipole moment and anapole moment are also improved substantially from previous searches, with corresponding tightest upper limits of $2.6 \times 10^{-11}e$, $4.8 \times 10^{-10}$ Bohr magnetons, $1.2 \times 10^{-23}$ ecm and $1.6 \times 10 ^{-33} cm^{2}$, respectively, for a dark matter mass of 20–40 $GeV / c^{2}$.

A Search for Spin-independent and Spin-dependent Dark Matter Using PandaX-4T Detector

Thu, 13 Apr 2023 00:00:00 +0800

PandaX-4T: First Analysis

Sun, 29 Jan 2023 00:00:00 +0800

DOI: https://doi.org/10.1103/PhysRevLett.127.261802

Data used in PandaX-4T first analysis, published in our 2021 PRL paper Dark Matter Search Results from the PandaX-4T Commissioning Run.

Search for Solar 8^B Neutrinos in the PandaX-4T Experiment Using Neutrino-Nucleus Coherent Scattering

Wed, 11 Jan 2023 00:00:00 +0800

A search for interactions from solar $^8B$ neutrinos elastically scattering off xenon nuclei using PandaX-4T commissioning data is reported. The energy threshold of this search is further lowered compared with the previous search for dark matter, with various techniques utilized to suppress the background that emerges from data with the lowered threshold. A blind analysis is performed on the data with an effective exposure of 0.48 tonne year, and no significant excess of events is observed. Among the results obtained using the neutrino-nucleus coherent scattering, our results give the best constraint on the solar $^8B$ neutrino flux. We further provide a more stringent limit on the cross section between dark matter and nucleon in the mass range from 3 to 9 $GeV/c^2$.

Search for Fermionic Dark Matter Absorption Signal with PandaX-4T Detector

Tue, 01 Nov 2022 00:00:00 +0800

Measurement of double beta decay half-life of 136Xe with the PandaX-4T detector

Tue, 25 Oct 2022 00:00:00 +0800

Precise measurement of two-neutrino double beta decay (DBD) half-life is an important step for the searches of Majorana neutrinos with neutrinoless double-beta decay. We report the measurement of DBD half-life of ${}^{136}Xe$ using the PandaX-4T dual-phase Time Projection Chamber (TPC) with 3.7-tonne natural xenon and the first 94.9-day physics data release. The background model in the fiducial volume is well constrained in situ by events in the outer active region. With a ${}^{136}Xe$ exposure of 15.5 kg-year, we establish the half-life as 2.27±0.03(stat.)±0.10(syst.) $\times 10^{21}$ year. This is the first DBD half-life measurement with natural xenon and demonstrates the physics capability of a large-scale liquid xenon TPC in the field of rare event searches.

Searches on Weakly Interacting Massive Particles and sub-MeV Fermionic Dark Matter in PandaX-II and PandaX-4T

Fri, 14 Oct 2022 00:00:00 +0800

First search for the absorption of fermionic dark matter with the PandaX-4T experiment

Thu, 13 Oct 2022 00:00:00 +0800

Compared to the signature of dark matter elastic scattering off nuclei, absorption of fermionic dark matter by nuclei opens up a new searching channel for light dark matter with a characteristic mono-energetic signal. In this letter, we explore the 95.0-day data from PandaX-4T commissioning run and report the first dedicated searching results of the fermionic dark matter absorption signal through neutral current process. No significant signal was found and the lowest limit on the dark matter-nucleon interaction cross section is set to be $ 1.5 \times 10^{-50} cm^{2} $ for a fermionic dark matter mass of $40 MeV / c^{2}$ with 90% confidence level.

Search for light fermionic dark matter absorption on electrons in PandaX-4T

Thu, 13 Oct 2022 00:00:00 +0800

We report a search on sub-MeV fermionic dark matter absorbed by electrons with an outgoing active neutrino using the $0.63$ tonne year exposure collected by the PandaX-4T liquid xenon experiment. No significant signals are observed over the expected background. The data are interpreted into limits to the effective couplings between such dark matter and the electron. For axial-vector or vector interactions, our sensitivity is competitive in comparison to existing astrophysical bounds on the decay of such a dark matter candidate into photon final states. In particular, we present the first direct detection limits for a vector (axial-vector) interaction which are the strongest in the mass range from $35$ to $55$ ($25$ to $45$) $keV/c^2$ in comparison to other astrophysical and cosmological constraints.

Constraints on the axial-vector and pseudo-scalar mediated WIMP-nucleus interactions from PandaX-4T experiment

Mon, 03 Oct 2022 00:00:00 +0800

We present the constraints on the axial-vector and pseudo-scalar mediated WIMP-nucleus interactions from the PandaX-4T experiment, using the data set corresponding to a total exposure of 0.63 tonne⋅year. No significant signal excess is observed, and the most stringent upper limits to date on the spin-dependent WIMP-neutron scattering cross section are set at 90% confidence level with the minimum WIMP-neutron scattering cross section of $5.8\times 10^{-42}cm^{2}$ for WIMP mass of 40 $GeV/c^{2}$. Exclusion limits on the axial-vector and pseudo-scalar simplified models are also derived.

A search for two-component Majorana dark matter in a simplified model using the full exposure data of PandaX-II experiment

Sat, 10 Sep 2022 00:00:00 +0800

In the two-component Majorana dark matter model, one dark matter particle can scatter off the target nuclei, and turn into a slightly heavier component. In the framework of a simplified model with a vector boson mediator, both the tree-level and loop-level processes contribute to the signal in direct detection experiment. In this paper, we report the search results for such dark matter from PandaX-II experiment, using total data of the full 100.7 tonne⋅day exposure. No significant excess is observed, so strong constraints on the combined parameter space of mediator mass and dark matter mass are derived. With the complementary search results from collider experiments, a large range of parameter space can be excluded.

Study of background from accidental coincidence signals in the PandaX-II experiment

Thu, 18 Aug 2022 00:00:00 +0800

Study of background from accidental coincidence signals in the PandaX-II experiment

Data acquisition system on PandaX dark matter detection experiment and self-interacting dark matter detection

Fri, 05 Aug 2022 00:00:00 +0800

Neutron-induced nuclear recoil background in the PandaX-4T experiment

Fri, 29 Jul 2022 00:00:00 +0800

Neutron-induced nuclear recoil background is critical to the dark matter searches in the PandaX-4T liquid xenon experiment. This paper studies the feature of neutron background in liquid xenon and evaluates their contribution in the single scattering nuclear recoil events through three methods. The first method is fully Monte Carlo simulation based. The last two are data-driven methods that also use the multiple scattering signals and high energy signals in the data, respectively. In the PandaX-4T commissioning data with an exposure of 0.63 tonne⋅year, all these methods give a consistent result that there are 1.15±0.57 neutron-induced background in dark matter signal region within an approximated nuclear recoil energy window between 5 and 100 keV.

Physics in the MeV range with PandaX-4T: measurement of double beta decay half-life of Xe-136

Tue, 12 Jul 2022 15:00:00 +0800

PandaX-4T is not just a dark matter detector, as you may be more familiar with. For such a large and exquisite detector, we can explore multiple physics topics. Neutrino physics is one such important direction.

Precise measurement of two-neutrino double beta decay (DBD) half-life is an important step for the searches of Majorana neutrinos with neutrinoless double-beta decay. We report the measurement of DBD half-life of Xe-136 using the PandaX-4T. With 3.7-tonne natural xenon, we have accumulated a large number of DBD events in the first 94.9-day commissioning data. With a Xe-136 exposure of 15.5 kg-year, we establish the half-life as 2.27 ± 0.03(stat.) ± 0.09(syst.) × 10²¹ year.

PandaX’s first attempt to “see” the solar neutrino floor

Sat, 09 Jul 2022 21:00:00 +0800

Background neutrinos can elastically scatter with target nucleus (coherently elastic neutrino-nucleus scattering or CEvNS), producing nuclear recoil signals in a dark matter detector that can mimic dark matter signals. This intrinsic background is the so-called “neutrino floor”, which will ultimately limit the sensitivity of dark matter direct detection. On the other hand, it also provides very interesting physics opportunities to study neutrino interactions. A first search for solar ⁸B neutrino CEvNS on xenon using PandaX-4T is carried out using the commissioning data set. The energy threshold of this search is further lowered compared to previous search for dark matter, with various techniques utilized to suppress the background that emerges from data with the lowered threshold. A blind analysis is performed on data with an effective exposure of 0.48 tonne-year and no significant excess of events is observed. Among results obtained using neutrino-nucleus coherent scattering, our results give the best constraint on solar ⁸B neutrino flux. We further provide more stringent limit on cross section between dark matter and nucleon in the mass range from 3 to 10 GeV. The paper has been submitted to arXiv and PRL. You may also find it here.

Low radioactive material screening and background control for the PandaX-4T experiment

Mon, 27 Jun 2022 00:00:00 +0800

PandaX-4T is a ton-scale dark matter direct detection experiment using a dual-phase TPC technique at the China Jinping Underground Laboratory. Various ultra-low background technologies have been developed and applied to material screening for PandaX·4T, including HPGe gamma spectroscopy, ICP-MS, NAA, radon emanation measurement system, krypton assay station, and alpha detection system. Low background materials were selected to assemble the detector. Surface treatment procedures were investigated to further suppress radioactive background. Combining measured results and Monte Carlo simulation, the total material background rates of PandaX-4T in the energy region of $1–25$ $keV_{ee}$ are estimated to be $(9.9 ± 1.9)$ $\times$ $10^{−3} $mDRU$ for electron recoil and $(2.8 ± 0.6)$ $\times$ $10^{−4}$ $mDRU$ for nuclear recoil. In addition, ${}^{nat}Kr$ in the detector is estimated to be < $8$ $ppt$.

Search for sub-GeV dark matter with a new diurnal modulation signature

Wed, 27 Apr 2022 15:45:00 +0800

With the extra energy gained from the cosmic rays, sub-GeV dark matter particles can produce visible recoil signals in the detector. We present a new result searching for the cosmic ray boosted dark matter (CRDM) with the PandaX-II full data. This work is motivated by the theoretical paper (PRL. 126 091804), which first pointed out that a sidereal diurnal modulation in signal rate and energy spectrum due to the Earth shielding is expected for low mass CRDM.

Specifically, detailed Jinping Mountain geometry is implemented with a realistic simulation on the scatterings between the DM and Earth nuclei. We reanalyzed the PandaX-II data with additional sidereal time information. Based on PandaX-II data, and thanks to the low background level and large exposure, our result excludes the dark matter-nucleon elastic scattering cross section between 10^-31 cm² and 10^-28 cm² for a dark matter masses from 0.1 MeV/c² to 0.1 GeV/c² ,which covers a large unexplored parameter space and provides new information beyond the cosmological and astrophysical probes.

Search for Cosmic-Ray Boosted Sub-GeV Dark Matter at the PandaX-II Experiment

Wed, 27 Apr 2022 00:00:00 +0800

We report a novel search for the cosmic-ray boosted dark matter using the 100 tonne · day full dataset of the PandaX-II detector located at the China Jinping Underground Laboratory. With the extra energy gained from the cosmic rays, sub-GeV dark matter particles can produce visible recoil signals in the detector. The diurnal modulations in rate and energy spectrum are utilized to further enhance the signal sensitivity. Our result excludes the dark matter–nucleon elastic scattering cross section between 10⁻³¹and 10⁻²⁸ cm² for dark matter masses from 0.1 MeV/c² to 0.1 GeV/c², with a large parameter space previously unexplored by experimental collaborations.

PandaX-4T published the first result in Physics Review Letters, giving the strongest WIMP-nucleon interaction constraint!

Mon, 17 Jan 2022 17:15:00 +0800

On December 24, 2021, the first dark matter search result from PandaX-4T, a liquid xenon detection experiment, was published in Physical Review Letters as the “Editor’s Suggestion” [1]. The American Physical Society 《Physics》 reported this PandaX-4T latest result together with another result from the Axion Dark Matter Experiment with a title of “Tightening the Net on Two Kinds of Dark Matter”

${}^{83}Rb$/$ {}^{83m}Kr$ production and cross-section measurement with 3.4 MeV and 20 MeV proton beams

Wed, 05 Jan 2022 00:00:00 +0800

${}^{83m}Kr$ with a short lifetime is an ideal calibration source for liquid xenon or liquid argon detector. The ${}^{83m}Kr$ isomer can be generated through the decay of ${}^{83}Rb$ isotope, and ${}^{83}Rb$ is usually produced by proton beams bombarding natural krypton atoms. In this paper, we report a successful production of ${}^{83}Rb$/$ {}^{83m}Kr$ with $3.4$ $MeV$ proton beam energy and measure the production rate with such low proton energy for the first time. Another production attempt was performed with newly available 20 MeV proton beam in China, the production rate is consistent with our expectation. The produced ${}^{83m}Kr$ source has been successfully injected into PandaX-II liquid xenon detector and yielded enough statistics for detector calibration.

Light yield and field dependence measurement in PandaX-II dual-phase xenon detector

Wed, 05 Jan 2022 00:00:00 +0800

The dual-phase xenon detector is one of the most sensitive detectors for dark matter direct detection, where the energy deposition of incoming particles can be converted into light and electrons through xenon excitation and ionization. The detector response to signal energy deposition varies significantly with the electric field in liquid xenon . We study the detector light yield and its dependence on the electric field in PandaX-II dual-phase detector containing 580 kg liquid xenon in the sensitive volume. From measurement, the light yield at electric field from 0 V/cm to 317 V/cm is obtained for energy deposition up to 236 keV.

Dark Matter Search Results from the PandaX-4T Commissioning Run

Thu, 23 Dec 2021 00:00:00 +0800

We report the first dark matter search results using the commissioning data from PandaX-4T. Using a time projection chamber with 3.7-tonne of liquid xenon target and an exposure of 0.63~tonne⋅year, 1058 candidate events are identified within an approximate electron equivalent energy window between 1 and 30 $keV$. No significant excess over background is observed. Our data set a stringent limit to the dark matter-nucleon spin-independent interactions, with a lowest excluded cross section (90% C.L.) of $3.3 \times 10^{−47}cm^2$ at a dark matter mass of 30 $GeV/c^2$.

PandaX-4T cryogenic distillation system for removing krypton from xenon

Mon, 20 Dec 2021 00:00:00 +0800

An efficient cryogenic distillation system was designed and constructed for the PandaX-4T dark matter detector based on the McCabe–Thiele method and the conservation of mass and energy. This distillation system is designed to reduce the concentration of krypton in commercial xenon from $5$ $\times$ $10^{−7}$ to $\sim$ $10^{−14}$ $mol/mol$ with $99\%$ xenon collection efficiency at a maximum flow rate of $10$ $kg/h$. The offline distillation operation has been completed and $5.75$ tons of ultra-high purity xenon was produced, which is used as the detection medium in the PandaX4T detector. The krypton concentration of the product xenon is measured with an upper limit of $8.0$ $ppt$. The construction, operation, and stable purification performance of the cryogenic distillation system are studied with the experimental data, which is important for theoretical research and distillation operation optimization.

A 500 MS/s waveform digitizer for PandaX dark matter experiments

Fri, 10 Dec 2021 00:00:00 +0800

Waveform digitizers are key readout instruments in particle physics experiments. In this paper, we present a waveform digitizer for the PandaX dark matter experiments. It supports both external-trigger readout and triggerless readout, accommodating the needs of low rate full-waveform readout and channel-independent low threshold acquisition, respectively. This digitizer is a 8-channel VME board with a sampling rate of 500 MS/s and 14-bit resolution for each channel. A digitizer system consisting of 72 channels has been tested in situ of the PandaX-4T experiment. We report the system performance with real data.

Performance of cryogenic demountable indium seal at high pressures

Mon, 13 Sep 2021 00:00:00 +0800

An essential challenge in seal design is to provide an ultra-low leak rate at cryogenic temperatures and high pressures. In this paper, the performance of demountable indium seals under a charging pressure of 8.5 MPa A and at cryogenic temperatures down to −190 °C was investigated. Three indium seal structures with a diameter of 30 mm were specifically designed and tested. All three structures went through both room temperature and cryogenic temperature tests in cycles with a pressure of up to 8.5 MPa A. In addition, leak rate experiments regarding the creep relaxation effect of the indium ring were conducted. The results showed that the leak rates of all three structures were lower than $1 \times 10^{-10} Pa\thinspace m^{3} s^{-1}$ at both room temperature and cryogenic temperature with the pressure up to 8.5 MPa A when the torque was 8 or 12 N m. It was concluded that the linear loads for achieving a successful indium seal were 163, 171, and $220 N mm^{-1}$ alongside its circumference for the 2 mm indium M-T structure, the 3 mm indium M-T structure, and the Z-shaped seal structure, respectively. Furthermore, although the torque slightly dropped after the assembly due to the creep relaxation effect, the leak rates of the structure were still lower than $1 \times 10^{-10} Pa\thinspace m^{3} s^{-1}$ three days after the assembly. The present work is helpful for designing ultra-low leak rate demountable indium seals at cryogenic temperatures and high pressures.

BambooMC -- A Geant4-based simulation program for the PandaX experiments

Wed, 25 Aug 2021 00:00:00 +0800

The purpose of the PandaX experiments is to search for the possible events resulted from dark matter particles, neutrinoless double beta decay or other rare processes with xenon detectors. Understanding the energy depositions from backgrounds or calibration sources in these detectors is very important. The program of BambooMC is created to perform the Geant4-based Monte Carlo simulation, providing reference information for the experiments. We introduce the design and features of BambooMC in this report. The running of the program depends on a configuration file, which combines different detectors, event generators, physics lists and analysis packs together in one simulation. The program can be easily extended and applied to other experiments.

Constraining self-interacting dark matter with the full dataset of PandaX-II

Wed, 11 Aug 2021 00:00:00 +0800

Self-interacting dark matter (SIDM) is a leading candidate proposed to solve discrepancies between predictions of the prevailing cold dark matter theory and observations of galaxies. Many SIDM models predict the existence of a light force carrier that mediates strong dark matter self-interactions. If the mediator couples to the standard model particles, it could produce characteristic signals in dark matter direct detection experiments. We report searches for signals of SIDM models with a light mediator using the full dataset of the PandaX-II experiment, basing on a total exposure of 132 tonne-days. No significant excess over background is found, and our likelihood analysis leads to a strong upper limit on the dark matter-nucleon coupling strength. We further combine the PandaX-II constraints and those from observations of the light element abundances in the early universe, and show that direct detection and cosmological probes can provide complementary constraints on dark matter models with a light mediator.

Design and commissioning of the PandaX-4T cryogenic distillation system for krypton and radon removal

Fri, 23 Jul 2021 00:00:00 +0800

An online cryogenic distillation system for the removal of krypton and radon from xenon was designed and constructed for PandaX-4T, a highly sensitive dark matter detection experiment. The krypton content in a commercial xenon product is expected to be reduced by $7$ orders of magnitude with $99\%$ xenon collection efficiency at a flow rate of $10$ $kg/h$ by design. The same system can reduce radon content in xenon by reversed operation, with an expected radon reduction factor of about $1.8$ in PandaX-4T under a flow rate of $56.5$ $kg/h$. The commissioning of this system was completed, with krypton and radon operations tested under respective working conditions. The krypton concentration of the product xenon was measured with an upper limit of $8.0$ $ppt$.

The Cryogenics and Xenon handling system for the PandaX-4T Experiment

Sat, 05 Jun 2021 00:00:00 +0800

PandaX-4T, the new generation of the PandaX detector, is a xenon dual-phase detector with about six tons of liquid xenon as target for dark matter search. A cryogenics and xenon handling system is designed to liquify and purify this large detector. In this paper, the results on the commission of the cryogenics and gas handling system are reported. The maximum cooling power of ~ 580 W at 178 K with three cooperating coldheads has been achieved. The filling rate with an assisted liquid nitrogen cooling can reach ~ 700 kg/day. The average rate of recuperation by liquid nitrogen is around 440 kg/day. The maximum total purification speed of two circulation loops is up to ~ 155 slpm. Each loop is using a large heat exchanger with a measured heat exchange efficiency of ~ 97.5+-0.5%.

PandaX collaboration published a new result of light dark matter searching in Physics Review Letters

Fri, 04 Jun 2021 12:30:00 +0800

A new result on searching of light dark matter (DM) with PandaX-II experimental data was published online in Physical Review Letters on May 28, 2021 with a title of “Search for Light Dark Matter–Electron Scattering in the PandaX-II Experiment “[1]. This is the 6th PRL paper published with PandaX-II data.

Search for Light Dark Matter-Electron Scatterings in the PandaX-II Experiment

Fri, 28 May 2021 00:00:00 +0800

We report constraints on light dark matter through its interactions with shell electrons in the PandaX-II liquid xenon detector with a total 46.9 tonnes⋅day exposure. To effectively search for these very low energy electron recoils, ionization-only signals are selected from the data. 1821 candidates are identified within an ionization signal range between 50 and 75 photoelectrons, corresponding to a mean electronic recoil energy from 0.08 to 0.15 $keV$. The 90% C.L. exclusion limit on the scattering cross section between the dark matter and electron is calculated with systematic uncertainties properly taken into account. Under the assumption of point interaction, we provide the world’s most stringent limit within the dark matter mass range from 15 to 30 $MeV/c^2$, with the corresponding cross section from $2.5 \times 10^{-37}$ to $3.1 \times 10^{−38} cm^2$.

Determination of responses of liquid xenon to low energy electron and nuclear recoils using the PandaX-II detector

Wed, 21 Apr 2021 00:00:00 +0800

We report a systematic determination of the responses of PandaX-II, a dual phase xenon time projection chamber detector, to low energy recoils. The electron recoil (ER) and nuclear recoil (NR) responses are calibrated, respectively, with injected tritiated methane or ${}^{220}Rn$ source, and with ${}^{241}Am-Be$ neutron source, within an energy range from 1-25 keV (ER) and 4-80 keV (NR), under the two drift fields of 400 and 317 V/cm. An empirical model is used to fit the light yield and charge yield for both types of recoils. The best fit models can well describe the calibration data. The systematic uncertainties of the fitted models are obtained via statistical comparison against the data.

Diurnal effect of sub-GeV dark matter boosted by cosmic rays

Fri, 05 Mar 2021 00:00:00 +0800

We point out a new type of diurnal effect for the cosmic ray boosted dark matter (DM). The DM-nucleon interactions not only allow the direct detection of DM with nuclear recoils but also allow cosmic rays to scatter with and boost the nonrelativistic DM to higher energies. If the DM-nuclei scattering cross sections are sufficiently large, the DM flux is attenuated as it propagates through the Earth, leading to a strong diurnal modulation. This diurnal modulation provides another prominent signature for the direct detection of boosted sub-GeV DM, in addition to signals with higher recoil energy.

Latest progress report and future plan

Sun, 17 Jan 2021 13:15:00 +0800

The PandaX (particle and astrophysical xenon) observatory uses xenon as target and detector to search for WIMP particles as well as neutrinoless double beta decay ($0\nu\beta\beta$) in ${}^{136}Xe$. At present, the PandaX-II experiment is completed and the PandaX-4T experiment is under installation. The future PandaX program will focus on the following two main directions:

Develop PandaX-4T into a multi-purpose liquid xenon experiment, to push further the dark matter search and other physics topics;
Develop and operate a 100-kg high pressure gas TPC (HpgTPC), PandaX-III, as a pathfinder for a tracking calorimeter to search for $0\nu\beta\beta$ in ${}^{136}Xe$.

The full International Advisory Committee 2020 Report.

PandaX Annual Report 2021

Fri, 01 Jan 2021 00:00:00 +0800

The PandaX (particle and astrophysical xenon) observatory uses xenon as target and detector to search for WIMP particles as well as neutrinoless double beta decay (NLDBD) in ${}^{136}Xe$. PandaX-4T experiment has started operation in 2021. The future PandaX program will focus on the following two main directions:

Internal calibration of the PandaX-II detector with radon gaseous sources

Thu, 31 Dec 2020 00:00:00 +0800

We have developed a low-energy electron recoil (ER) calibration method with ${}^{220}Rn$ for the PandaX-II detector. ${}^{220}Rn$, emanated from natural thorium compounds, was fed into the detector through the xenon purification system. From 2017 to 2019, we performed three dedicated calibration campaigns with different radon sources. We studied the detector response to $\alpha$, $\beta$, and $\gamma$ particles with focus on low energy ER events. During the runs in 2017 and 2018, the amount of radioactivity of ${}^{222}Rn$ were on the order of $1\%$ of that of ${}^{220}Rn$ and thorium particulate contamination was negligible, especially in 2018. We also measured the background contribution from ${}^{214}Pb$ for the first time in PandaX-II with the help from a ${}^{222}Rn$ injection. Calibration strategy with ${}^{220}Rn$ and ${}^{222}Rn$ will be implemented in the upcoming PandaX-4T experiment and can be useful for other xenon-based detectors as well.

An improved design of the readout base board of the photomultiplier tube for future PandaX dark matter experiments

Sun, 06 Dec 2020 00:00:00 +0800

The PandaX project consists of a series of xenon-based experiments that are used to search for dark matter (DM) particles and to study the fundamental properties of neutrinos. The next DM experiment PandaX-4T will be using 4 ton liquid xenon in the sensitive volume, which is nearly a factor of seven larger than that of the previous experiment PandaX-II. Due to the increasing target mass, the sensitivity of searching for both DM and neutrinoless double-beta decay ($0\nu\beta\beta$) signals in the same detector will be significantly improved. However, the typical energy of interest for $0\nu\beta\beta$ signals is at the MeV scale, which is much higher than that of most popular DM signals. In the baseline readout scheme of the photomultiplier tubes (PMTs), the dynamic range is very limited. Signals from the majority of PMTs in the top array of the detector are heavily saturated at MeV energies. This deteriorates the $0\nu\beta\beta$ search sensitivity. In this paper we report a new design of the readout base board of the PMTs for future PandaX DM experiments and present its improved performance on the dynamic range.

PandaX-II Experiment for Dark Matter Search

Fri, 30 Oct 2020 00:00:00 +0800

A search for solar axions and anomalous neutrino magnetic moment with the complete PandaX-II data

Thu, 27 Aug 2020 00:00:00 +0800

We report a search for new physics signals using the low energy electron recoil events in the complete data set from PandaX-II, in light of the recent event excess reported by XENON1T. The data correspond to a total exposure of 100.7 ton-day with liquid xenon. With robust estimates of the dominant background spectra, we perform sensitive searches on solar axions and neutrinos with enhanced magnetic moment. We find that the axion-electron coupling $g_{Ae} \lt 4.6\times 10^{-12}$ for an axion mass less than $\rm 0.1~keV/c^2$ and the neutrino magnetic moment $μ_ν \lt 3.2\times 10^{-11}μ_{B}$ at 90% confidence level. The observed excess from XENON1T is within our experimental constraints.

Results of Dark Matter Search using the Full PandaX-II Exposure

Thu, 27 Aug 2020 00:00:00 +0800

We report the dark matter search results using the full 132 ton⋅day exposure of the PandaX-II experiment, including all data from March 2016 to August 2018. No significant excess of events were identified above the expected background. Upper limits are set on the spin-independent dark matter-nucleon interactions. The lowest 90% confidence level exclusion on the spin-independent cross section is $2.0 \times 10^{−46} cm^{2}$ at a WIMP mass of 15 $GeV / c^{2}$.

New WIMP and axion search results from complete exposure of PandaX-II released

Wed, 26 Aug 2020 10:15:00 +0800

The PandaX collaboration released the latest results on the search of WIMPs and axions based on the full exposure of data at the International High Energy Physics Conference (ichep2020) on July 30, 2020 (PDF). Detailed analyses were reported with an online seminar on August 20(PDF1, PDF2 ). The most stringent constraint is set for WIMPs around $10 GeV/c^{2}$ using the nuclear recoil events. The intriguing electron recoil event excess observed by XENON1T [1] was tested with the electron recoil data, and was found to be within the constraint of the PandaX-II data.

PandaX Annual Report 2020

Wed, 01 Jan 2020 00:00:00 +0800

An Improved Evaluation of the Neutron Background in the PandaX-II Experiment

Sat, 09 Nov 2019 00:00:00 +0800

In dark matter direct detection experiments, neutron is a serious source of background, which can mimic the dark matter-nucleus scattering signals. In this paper, we present an improved evaluation of the neutron background in the PandaX-II dark matter experiment by a novel approach. Instead of fully relying on the Monte Carlo simulation, the overall neutron background is determined from the neutron-induced high energy signals in the data. In addition, the probability of producing a dark-matter-like background per neutron is evaluated with a complete Monte Carlo generator, where the correlated emission of neutron(s) and $\gamma$(s) in the ($\alpha$, n) reactions and spontaneous fissions is taken into consideration. With this method, the neutron backgrounds in the Run 9 (26-ton-day) and Run 10 (28-ton-day) data sets of PandaX-II are estimated to be 0.66±0.24 and 0.47±0.25 events, respectively.

Searching for neutrino-less double beta decay of 136Xe with PandaX-II liquid xenon detector

Mon, 16 Sep 2019 00:00:00 +0800

We report the Neutrino-less Double Beta Decay (NLDBD) search results from PandaX-II dual-phase liquid xenon time projection chamber. The total live time used in this analysis is 403.1 days from June 2016 to August 2018. With NLDBD-optimized event selection criteria, we obtain a fiducial mass of 219 kg of natural xenon. The accumulated xenon exposure is 242 kg $\cdotp$ yr, or equivalently 22.2 kg $\cdotp$ yr of ${}^{136}Xe$ exposure. At the region around ${}^{136}Xe$ decay Q-value of 2458 keV, the energy resolution of PandaX-II is 4.2%. We find no evidence of NLDBD in PandaX-II and establish a lower limit for decay half-life of 2.1$\times 10^{23}$ yr at the 90% confidence level, which corresponds to an effective Majorana neutrino mass $m_{\beta \beta}\lt$ (1.4 - 3.7) eV. This is the first NLDBD result reported from a dual-phase xenon experiment.

PandaX-II Dark Matter Experiment and the PandaX-4T Cryogenics, Circulation and Distillation System

Thu, 05 Sep 2019 00:00:00 +0800

A search of spin-dependent WIMP-nucleon interactions using the PandaX-II detector

Sun, 01 Sep 2019 00:00:00 +0800

PandaX-II dark matter detector and its first results

Fri, 14 Jun 2019 00:00:00 +0800

PandaX Annual Report 2019

Tue, 01 Jan 2019 00:00:00 +0800

Executive summary: PandaX (particle and astrophysical xenon) observatory uses xenon as target to search for WIMP particles and to study fundamental properties of neutrinos. In summer 2019, the PandaX-II experiment accomplished all the designed goals, and the operation was officially terminated. The total dark matter exposure is about 140-ton-day. The collaboration has been focusing on constructing the PandaX-4T (4-ton liquid xenon target) experiment in the B2 hall of CJPL-II. In parallel, the PandaX-III experiment, with a 100-kg high pressure gas xenon TPC (HpgTPC), is being prepared at SJTU. This is a technological pathfinder for this unique approach to search for the neutrinoless double beta decay ($0\nu\beta\beta$) in ${}^{136}Xe$.

Dark matter direct search sensitivity of the PandaX-4T experiment

Fri, 17 Aug 2018 00:00:00 +0800

The PandaX-4T experiment, a 4-ton scale dark matter direct detection experiment, is being planned at the China Jinping Un- derground Laboratory. In this paper we present a simulation study of the expected background in this experiment. In a 2.8-ton fiducial mass and the signal region between 1-10 keV electron equivalent energy, the total electron recoil background is found to be $4.9 \times 10^{5} kg^{-1}d^{-1}keV^{-1}$. The nuclear recoil background in the same region is $2.8 \times 10^{-7} kg^{-1}d^{-1}keV^{-1}$. With an exposure of 5.6 ton-years, the sensitivity of PandaX-4T could reach a minimum spin-independent dark matter-nucleon cross section of $6 \times 10^{-48}cm^{2}$ at a dark matter mass of 40 $GeV/c^{2}$.

Signal-background discrimination with convolutional neural networks in the PandaX-III experiment using MC simulation

Thu, 09 Aug 2018 00:00:00 +0800

The PandaX-III experiment will search for neutrinoless double beta decay of ${}^{136}Xe$ with high pressure gaseous time projection chambers at the China Jin-Ping underground Laboratory. The tracking feature of gaseous detectors helps suppress the background level, resulting in the improvement of the detection sensitivity. We study a method based on the convolutional neural networks to discriminate double beta decay signals against the background from high energy gammas generated by ${}^{214}Bi$ and ${}^{208}Tl$ decays based on detailed Monte Carlo simulation. Using the 2-dimensional projections of recorded tracks on two planes, the method successfully suppresses the background level by a factor larger than 100 with a high signal efficiency. An improvement of 62% on the efficiency ratio of $\epsilon_{s}/\sqrt{\epsilon_{b}}$ is achieved in comparison with the baseline in the PandaX-III conceptual design report.

Constraining Dark Matter Models with a Light Mediator at the PandaX-II Experiment

Thu, 12 Jul 2018 00:00:00 +0800

We search for nuclear recoil signals of dark matter models with a light mediator in PandaX-II, a direct detection experiment in the China Jinping underground laboratory. Using data collected in 2016 and 2017 runs, corresponding to a total exposure of 54 ton day, we set upper limits on the zero-momentum dark matter-nucleon cross section. These limits have a strong dependence on the mediator mass when it is comparable to or below the typical momentum transfer. We apply our results to constrain self-interacting dark matter models with a light mediator mixing with standard model particles, and set strong limits on the model parameter space for the dark matter mass ranging from 5 GeV to 10 TeV.

PandaX-II Constraints on Spin-Dependent WIMP-Nucleon Effective Interactions

Thu, 05 Jul 2018 00:00:00 +0800

We present PandaX-II constraints on candidate WIMP-nucleon effective interactions involving the nucleon or WIMP spin, including, in addition to standard axial spin-dependent (SD) scattering, various couplings among vector and axial currents, magnetic and electric dipole moments, and tensor interactions. The data set corresponding to a total exposure of 54-ton-days is reanalyzed to determine constraints as a function of the WIMP mass and isospin coupling. We obtain WIMP-nucleon cross section bounds of $1.6\times 10^{-41}cm^2$ and $9.0\times10^{-42}cm^2$ (90% c.l.) for neutron-only SD and tensor coupling, respectively, for a mass $M_{WIMP} ∼ 40 GeV/c^2$. The SD limits are the best currently available for $M_{WIMP} > 40 GeV/c^2$. We show that PandaX-II has reached a sensitivity sufficient to probe a variety of other candidate spin-dependent interactions at the weak scale.

Searches of Axions and Axion-like particles with PandaX-II

Wed, 13 Jun 2018 00:00:00 +0800

A study of the photosensor system performance and background from radioactive gases of the PandaX-I dark matter experiment

Fri, 01 Jun 2018 00:00:00 +0800

Design and commissioning of a 600 L Time Projection Chamber with Microbulk Micromegas

Fri, 01 Jun 2018 00:00:00 +0800

We report the design, construction, and initial commissioning results of a large high pressure gaseous Time Projection Chamber (TPC) with Micromegas modules for charge readout. The detector vessel has an inner volume of about 600 L and an active volume of 270 L. At 10 bar operating pressure, the active volume contains about 20 kg of xenon gas and can image charged particle tracks. Drift electrons are collected by the charge readout plane, which accommodates a tessellation of seven Micromegas modules. Each of the Micromegas covers a square of 20 cm by 20 cm. A new type of Microbulk Micromegas is chosen for this application due to its good gain uniformity and low radioactive contamination. Initial commissioning results with 1 Micromegas module running with 1 bar argon and isobutane gas mixture and 5 bar xenon and trimethylamine (TMA) gas mixture are reported. We also recorded extended background tracks from cosmic ray events and highlighted the unique tracking feature of this gaseous TPC.

PandaX Annual Report 2018

Mon, 01 Jan 2018 00:00:00 +0800

The PandaX (particle and astrophysical xenon) observatory uses xenon as target and detector to search for WIMP particles as well as neutrinoless double beta decay ($0\nu\beta\beta$) in ${}^{136}Xe$. Since the last IAC meeting in 2016, the PandaX-II experiment has been operated for two more years. The near future PandaX program will focus on the following three main directions:

Exploring the dark matter inelastic frontier with 79.6 days of PandaX-II data

Tue, 28 Nov 2017 00:00:00 +0800

We report here the results of searching for inelastic scattering of dark matter (initial and final state dark matter particles differ by a small mass splitting) with a nucleon for the first 79.6 days of PandaX-II data (Run 9). We set the upper limits for the spin independent weakly interactive massive particle–nucleon scattering cross section up to a mass splitting of $300 keV/c^{2}$ at two benchmark dark matter masses of 1 and $10 TeV/c^{2}$.

A Search of Spin-Independent WIMP-Nucleon Interactions using the PandaX-I and PandaX-II Detectors

Mon, 13 Nov 2017 00:00:00 +0800

PandaX-II published new results on the search of axions

Thu, 09 Nov 2017 06:30:00 +0800

New results on the detection of axions and galaxy axion-like particles (ALPs) with 80 days of PandaX-II data were published online in Physical Review Letters on Nov 1, 2017 (in the same issue as another PandaX-II paper on 54 ton-day WIMP search results). No positive signal was found by the most sensitive detector in the world, so the most stringent constraints on the properties of axions and ALPs were set.

Axion is a new type of particle proposed by Steven Weinberg and Frank Wilczek in the late 1970s to explain CP conservation in strong interactions. It is also one of the top candidates for dark matter. According to the theory, axions may interact with electrons and transfer all their energy to the electrons. By measuring the energetic electrons in the final state, experimentalists may determine the mass and coupling constant of axions with electrons.

Limits on Axion Couplings from the First 80 Days of Data of the PandaX-II Experiment

Wed, 01 Nov 2017 00:00:00 +0800

We report new searches for solar axions and galactic axionlike dark matter particles, using the first low-background data from the PandaX-II experiment at China Jinping Underground Laboratory, corresponding to a total exposure of about $2.7×10^{4}$ kg day. No solar axion or galactic axionlike dark matter particle candidate has been identified. The upper limit on the axion-electron coupling ($g_{Ae}$) from the solar flux is found to be about $4.35×10^{−12}$ in the mass range from $10^{-5}$ to $1 keV/c^{2}$ with 90% confidence level, similar to the recent LUX result. We also report a new best limit from the ${}^{57}Fe$ deexcitation. On the other hand, the upper limit from the galactic axions is on the order of $10^{-13}$ in the mass range from 1 to $10 keV/c^{2}$ with 90% confidence level, slightly improved compared with the LUX.

PandaX-II 54 Ton-day Results Published and Highlighted

Tue, 31 Oct 2017 10:00:00 +0800

Recent result from PandaX-II was published on Physical Review Letter (Phys. Rev. Lett. 119, 181302, “Editor’s Suggestion”) on October 30, 2017, back-to-back with the first result from XENON1T experiment. The papers are highlighted by a Physics “Viewpoint” commentary by Dan Hooper from FNAL and Univ. of Chicago, commenting that “… the latest results from two dark matter searches have further ruled out many theoretically attractive dark matter particle candidates …”, and “… representing the cutting edge in the search for dark matter …”.

Dark Matter Results From 54-Ton-Day Exposure of PandaX-II Experiment

Mon, 30 Oct 2017 00:00:00 +0800

We report a new search for weakly interacting massive particles (WIMPs) using the combined low background data sets acquired in 2016 and 2017 from the PandaX-II experiment in China. The latest data set contains a new exposure of 77.1 live days, with the background reduced to a level of $0.8×10^{-3} evt/kg/day$, improved by a factor of 2.5 in comparison to the previous run in 2016. No excess events are found above the expected background. With a total exposure of $5.4×10^{4}kg day$, the most stringent upper limit on the spin-independent WIMP-nucleon cross section is set for a WIMP with mass larger than $100 GeV/c^{2}$, with the lowest 90% C.L. exclusion at $8.6×10^{-47}cm^{2}$ at $40 GeV/c^{2}$.

PandaX-II released the official 54-ton-day WIMP search results

Fri, 01 Sep 2017 15:45:00 +0800

The PandaX-II collaboration released the official WIMP search results using 54 ton-day exposure on Aug. 23, 2017. No excess events were found above the expected background. The most stringent upper limit on spin-independent WIMP-nucleon cross section was set for a WIMP mass greater than $100 GeV/c^{2}$, with the lowest exclusion at $8.6\times10^{-47} cm^{2}$ at $40 GeV/c^{2}$. The result reported here is more conservative than the preliminary result shown during the TeVPA2017 conference, due to the adoption of updated photon/electron detection efficiencies.

A paper was submitted to Physical Review Letter with its preprint at http://arxiv.org/abs/arXiv:1708.06917.

Update of the trigger system of the PandaX-II experiment

Fri, 25 Aug 2017 00:00:00 +0800

PandaX-II experiment is a dark matter direct detection experiment using about half-ton of liquid xenon as the sensitive target. The electrical pulses detected by photomultiplier tubes from scintillation photons of xenon are recorded by waveform digitizers. The data acquisition of PandaX-II relies on a trigger system that generates common trigger signals for all waveform digitizers. Previously an analog device-based trigger system was used for the data acquisition system. In this paper we present a new FPGA-based trigger system. The design of this system and trigger algorithms are described. The performance of this system on real data is presented.

PandaX III

Wed, 09 Aug 2017 07:55:45 +0800

The PandaX-III project searches for the possible neutrinoless double-beta decay ($0\nu\beta\beta$) of ${}^{136}Xe$: ${}^{136}Xe \rightarrow {}^{136}Ba + 2e^-$ with 200 kg to one ton of 90% enriched ${}^{136}Xe$ as the source. The high-pressure gas Time Projection Chamber (TPC) we use can measure the energies of the two emitted electrons from $0\nu\beta\beta$ and image the electron tracks, and thus can effectively identify $0\nu\beta\beta$ signals and suppress the unwanted backgrounds.

Our TPC is symmetrical with the negative high voltage in the middle. Electrons ionized by an energy release in the TPC drift to either end, where Micromegas is used to amplify and collect the charges. The expected spatial resolution is 3 mm and the energy resolution is 3%.

New world-leading upper limit for spin independent WIMP-nucleon cross section from PandaX

Tue, 08 Aug 2017 00:30:00 +0800

Prof. Xiangdong Ji of Shanghai Jiao Tong University and University of Maryland, spokesperson of the PandaX Collaboration, announced new results on the dark matter (DM) search from the PandaX-II experiment on Monday Aug. 7, during the TeV Particle Astrophysics 2017 Conference at Columbus, Ohio, the United States. No DM candidate was identified within the data from an exposure of 54 ton-day, the largest reported DM direct detection data set to date. A world-leading 90% upper limit for the spin independent DM-nucleon cross section was set to be $6\times10^{-47}cm^{2}$ at the DM mass of $50 GeV/c^{2}$. Download the talk slides.

PandaX 4ton

Mon, 26 Jun 2017 08:59:57 +0800

After reaching the world-leading dark matter detection sensitivity with the PandaX-II (500 kg xenon) experiment in 2016, we are developing the next-generation dark matter experiment with a 4-tonne liquid xenon sensitive volume. The goal is to push the dark matter sensitivity down to $6\times10^{-48}$ cm$^{2}$ for spin-independent dark matter-nucleon scattering, a one-to-two order of magnitude improvement over the then-current sensitivity. Besides dark matter, PandaX 4ton also has good sensitivity to low-energy solar neutrinos and the neutrino magnetic moment. The $^{136}$Xe in the 4-tonne detector (natural abundance 8.9%) may produce neutrinoless double-beta decay signals; detecting such a mode would answer fundamental questions about neutrinos.

First dark matter search results from the PandaX-I experiment

Wed, 07 Jun 2017 00:00:00 +0800

We report on the first dark-matter (DM) search results from PandaX-I, a low threshold dual-phase xenon experiment operating at the China JinPing Underground Laboratory. In the 37-kg liquid xenon target with 17.4 live-days of exposure, no DM particle candidate event was found. This result sets a stringent limit for low-mass DM particles and disfavors the interpretation of previously-reported positive experimental results. The minimum upper limit, $3.7 × 10^{-44}cm^{2}$, for the spin-independent isoscalar DM-particle-nucleon scattering cross section is obtained at a DM-particle mass of $49GeV/c^{2}$ at 90% confidence level.

China Jin-Ping underground Laboratory

Sat, 27 May 2017 18:56:41 +0800

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Located in the middle of a 18-km tunnel under 2400 meters of rock overburden, in the Sichuan province of south-west China. As one of the deepest underground labs in the world, the CJPL has an extremely low flux of muon rate of less than $20/m^{2}/100$ day, which is about two orders of magnitude lower than the flux at the Gran Sasso underground laboratory (LNGS) in Italy. The low muon rate and the resulting background makes the lab ideal for a sensitive dark matter detection.

PandaX: Particle and Astrophysical Xenon Experiments

Thu, 25 May 2017 16:30:39 +0800

PandaX is designed to build and operate a ton-scale liquid xenon experiment to detect the so far elusive dark matter in the Universe. The PandaX experiment uses a two-phase (liquid and gas) xenon position-sensitive time projection chamber detector. It is located at CJPL, which is one of the deepest underground labs in the world. The program has evolved through a series of staged detectors — PandaX-I (120 kg), PandaX-II (580 kg), and PandaX-4T (3.7 tonnes) — and continues toward the multi-ten-tonne PandaX-20T, reaching sensitivities down to $10^{-47} cm^{2}$ for spin-independent WIMP-nucleon interactions and beyond.

PandaX-II dark matter experiment

PandaX-II is a dark matter direct detection experiment equipped with a half-ton scale dual-phase time projection chamber (TPC). The PandaX-II experiment started in Oct 2014 with the detector installation at CJPL, followed by about one year of engineering runs and tests. The commissioning run started on Nov 22, 2015. After collecting 19 days of effective data, this run stopped due to a high level of Krypton background. Nevertheless, a factor-of-two improvement on the spin-independent (SI) WIMP-nucleon cross section limits was obtained using this data compared to the final result from PandaX-I using 80 days of data. After a Krypton distillation campaign, the experiment restarted data taking in March 2016. The first physics run lasted until the end of June and collected 80 days of effective data. Combining the commissioning run and the first physics run, PandaX-II obtained the most stringent upper limits on the SI WIMP-nucleon cross sections for WIMPs with masses between 5 and 1000 GeV. The PandaX-II experiment concluded operation in June 2019.

Radioactive Background Control for PandaX Experiment and Corresponding Analysis

Thu, 27 Apr 2017 00:00:00 +0800

Current status of direct dark matter detection experiments

Thu, 02 Mar 2017 00:00:00 +0800

Much like ordinary matter, dark matter might consist of elementary particles, and weakly interacting massive particles are one of the prime suspects. During the past decade, the sensitivity of experiments trying to directly detect them has improved by three to four orders of magnitude, but solid evidence for their existence is yet to come. We overview the recent progress in direct dark matter detection experiments and discuss future directions.

Spin-Dependent Weakly-Interacting-Massive-Particle–Nucleon Cross Section Limits from First Data of PandaX-II Experiment

Wed, 01 Feb 2017 00:00:00 +0800

New constraints are presented on the spin-dependent weakly-interacting-massive-particle-(WIMP-)nucleon interaction from the PandaX-II experiment, using a data set corresponding to a total exposure of $3.3×10^{4}kg day$. Assuming a standard axial-vector spin-dependent WIMP interaction with ${}^{129}Xe$ and ${}^{131}Xe$ nuclei, the most stringent upper limits on WIMP-neutron cross sections for WIMPs with masses above $10 GeV/c^{2}$ are set in all dark matter direct detection experiments. The minimum upper limit of $4.1×10^{-41}cm^{2}$ at 90% confidence level is obtained for a WIMP mass of $40 GeV/c^{2}$. This represents more than a factor of 2 improvement on the best available limits at this and higher masses. These improved cross-section limits provide more stringent constraints on the effective WIMP-proton and WIMP-neutron couplings.

Krypton and radon background in the PandaX-I dark matter experiment

Sun, 01 Jan 2017 00:00:00 +0800

We discuss an in-situ evaluation of the ${}^{85}Kr$, ${}^{222}Rn$, and ${}^{220}Rn$ background in PandaX-I, a 120-kg liquid xenon dark matter direct detection experiment. Combining with a simulation, their contributions to the low energy electron-recoil background in the dark matter search region are obtained.

PandaX Collaboration

Fri, 23 Dec 2016 16:45:59 +0800

Project founder: Xiangdong Ji (xdji@sjtu.edu.cn)
Spokesperson: Jianglai Liu (jianglai.liu@sjtu.edu.cn)
Deputy spokesperson: Ning Zhou (nzhou@sjtu.edu.cn)
Publication committee: Yang Zhang (yangzhangsdu@sdu.edu.cn), Qing Lin (qinglin@ustc.edu.cn), Jianglai Liu (jianglai.liu@sjtu.edu.cn), Xiangdong Ji (xdji@sjtu.edu.cn)
Speaker committee: Qing Lin (qinglin@ustc.edu.cn), Junting Huang (junting@sjtu.edu.cn), Xianguo Lu (xianguo.lu@warwick.ac.uk). Please send talk invitations to this committee.

Collaboration institutions

PandaX is a collaboration of universities and research institutes in China and abroad. Full member institutes and technical collaborators are listed in the collaboration directory.

Internal links

Bylaws of the PandaX collaboration

PandaX Logbook

PandaX Docs

The PandaX-I Liquid Xenon Dark Matter Direct Detection Experiment: Cryogenic Design, Construction and Experimental Data Analysis

Sat, 03 Dec 2016 00:00:00 +0800

The future plan of the PandaX experiment

Sun, 06 Nov 2016 11:30:00 +0800

The PandaX observatory uses xenon as target and detector to search for WIMP particles as well as neutrinoless double beta decay ($0\nu\beta\beta$) in ${}^{136}Xe$. At present, the PandaX-II experiment is in operation in CJPL-I. The future PandaX program will pursue the following three main directions:

Continue the operation of PandaX-II until a total of 2-year exposure;
Develop and operate a multi-ton multi-purpose liquid xenon experiment, PandaX-xT, to push further the dark matter search;
Develop and operate a 200 kg (upgradable to ton-scale) high pressure gas TPC (HpgTPC), PandaX-III, to search for $0\nu\beta\beta$ in ${}^{136}Xe$.

Detail Report

PRL Published Dark Matter Results From the PandaX-II Experiment

Fri, 16 Sep 2016 00:45:00 +0800

The largest running dark-matter experiment has its first result: No finding yet with the world best sensitivity

Fri, 22 Jul 2016 01:00:00 +0800

Xiangdong Ji, Spokesperson and Project Leader of the PandaX experiment located in the China Jin-Ping underground Laboratory (CJPL), announced the first dark matter search results from the PandaX-II 500 kg liquid xenon detector in the 2016 International Identification of Dark Matter conference at Sheffield, UK in the evening of July 21, 2016 (Beijing Time). He reported that no trace of dark matter was observed with an exposure of 33,000 kg·day of liquid xenon, providing the newest constraints on the existence of dark matter. The sensitivity of the detection has reached the best level in the world. Download Slides

PandaX collaboration was founded in 2009 by Prof. Ji who splits his time between Shanghai Jiao Tong University and University of Maryland, USA. The collaboration consists of a numbers of institutions in China, including Shanghai Jiao Tong University, Peking University, Shandong University, Shanghai Institute of Applied Physics, Sun Yat-Sen University, University of Science and Technology of China, China Institute of Atomic Energy and Yalong Hydropower Company. Scientists from the University of Maryland and University of Michigan also joined the collaboration. The experimental hall of PandaX is located within the China JinPing underground Laboratory, which has been developed by the Tsinghua University and the Yalong Hydropower Company in 2010.

Material screening with HPGe counting station for PandaX experiment

Fri, 01 Jul 2016 00:00:00 +0800

A gamma counting station based on high-purity germanium (HPGe) detector was set up for the material screening of the PandaX dark matter experiments in the China Jinping Underground Laboratory. Low background gamma rate of 2.6 counts/min within the energy range of 20 to 2700 keV is achieved due to the well-designed passive shield. The sentivities of the HPGe detetector reach mBq/kg level for isotopes like K, U, Th, and even better for Co and Cs, resulted from the low-background rate and the high relative detection efficiency of 175%. The structure and performance of the counting station are described in this article. Detailed counting results for the radioactivity in materials used by the PandaX dark-matter experiment are presented. The upgrading plan of the counting station is also discussed.

Dark matter search results from the commissioning run of PandaX-II

Tue, 21 Jun 2016 00:00:00 +0800

We present the results of a search for weakly interacting massive particles (WIMPs) from the commissioning run of the PandaX-II experiment located at the China Jinping Underground Laboratory. A WIMP search data set with an exposure of $306 \times 19.1$ $kg·day$ was taken, while its dominant ${}^{85}Kr$ background was used as the electron recoil calibration. No WIMP candidates are identified, and a $90\%$ upper limit is set on the spin-independent elastic WIMP-nucleon cross section with a lowest excluded cross section of $2.97 \times 10^{−45}$ $cm^2$ at a WIMP mass of $44.7$ $GeV/c^2$.

Dark Matter Results from First 98.7 Days of Data from the PandaX-II Experiment

Fri, 03 Jun 2016 00:00:00 +0800

We report the weakly interacting massive particle (WIMP) dark matter search results using the first physics-run data of the PandaX-II 500 kg liquid xenon dual-phase time-projection chamber, operating at the China JinPing underground laboratory. No dark matter candidate is identified above background. In combination with the data set during the commissioning run, with a total exposure of $3.3×10^{4} kg day$, the most stringent limit to the spin-independent interaction between the ordinary and WIMP dark matter is set for a range of dark matter mass between $5$ and $1000 GeV/c^{2}$. The best upper limit on the scattering cross section is found $2.5×10^{-46}cm^{2}$ for the WIMP mass $40 GeV/c^{2}$ at 90% confidence level.

The electronics and data acquisition system for the PandaX-I dark matter experiment

Thu, 02 Jun 2016 00:00:00 +0800

We describe the electronics and data acquisition system used in the first phase of the PandaX experiment—a 120 kg dual-phase liquid xenon dark matter direct detection experiment in the China Jin-Ping Underground Laboratory. This system utilized 180 channels of commercial flash ADC waveform digitizers. During the entire experimental run, the system has achieved low trigger threshold (<1 keV electron-equivalent energy) and low deadtime data acquisition.

PandaX-I Experiment for Low-mass Dark Matter Search

Wed, 01 Jun 2016 00:00:00 +0800

Performance of photosensors in the PandaX-I experiment

Wed, 01 Jun 2016 00:00:00 +0800

We report the long term performance of the photosensors, 143 one-inch R8520-406 and 37 three-inch R11410-MOD photomultipliers from Hamamatsu, in the first phase of the PandaX dual-phase xenon dark matter experiment. This is the first time that a significant number of R11410 photomultiplier tubes were operated in liquid xenon for an extended period, providing important guidance to the future large xenon-based dark matter experiments.

Future plan of the PandaX Experiment, 2016

Fri, 01 Jan 2016 00:00:00 +0800

Probing Spin-Independent WIMP-Nucleon Interactions with the PandaX-I Detector

Thu, 31 Dec 2015 00:00:00 +0800

Design and Performance of Time Projection Chambers for the PandaX Dark Matter Detector

Wed, 02 Dec 2015 00:00:00 +0800

Searching for Low Mass Dark Matter with The PandaX Liquid Xenon Detector

Mon, 31 Aug 2015 00:00:00 +0800

Development and Experimental Study and Optimization of An Ultra High Purity Xenon/Krypton Cryogenic Distillation System

Fri, 10 Jul 2015 00:00:00 +0800

Low-mass dark matter search results from full exposure of the PandaX-I experiment

Mon, 01 Jun 2015 00:00:00 +0800

We report the results of a weakly interacting massive particle (WIMP) dark matter search using the full 80.1 live-day exposure of the first stage of the PandaX experiment (PandaX-I) located in the China Jin-Ping Underground Laboratory. The PandaX-I detector has been optimized for detecting low-mass WIMPs, achieving a photon detection efficiency of 9.6%. With a fiducial liquid xenon target mass of 54.0 kg, no significant excess events were found above the expected background. A profile likelihood ratio analysis confirms our earlier finding that the PandaX-I data disfavor all positive low-mass WIMP signals reported in the literature under standard assumptions. A stringent bound on a low-mass WIMP is set at a WIMP mass below $10 GeV/c^{2}$, demonstrating that liquid xenon detectors can be competitive for low-mass WIMP searches.

Design and Realization of Electronics and Data Acquisition System for the PandaX Experiment

Wed, 20 May 2015 00:00:00 +0800

PandaX: a liquid xenon dark matter experiment at CJPL

Tue, 03 Jun 2014 00:00:00 +0800

PandaX is a large liquid-xenon detector experiment usable for direct dark-matter detection and ${}^{136}Xe$ double-beta decay search. The central vessel was designed to accommodate a staged target volume increase from initially 120 kg (stage I) to 0.5 t (stage II) and eventually to a multi-ton scale. The experiment is located in the Jinping Deep-Underground Laboratory in Sichuan, China. The detector operates in dual-phase mode, allowing detection of both prompt scintillation, and ionization charge through proportional scintillation. In this paper a detailed description of the stage I detector design and performance as well as results established during the commissioning phase are presented.

Development of the liquid level meters for the PandaX dark matter detector

Sun, 01 Jun 2014 00:00:00 +0800

The two-phase xenon detector is at the frontier of dark matter direct search. This kind of detector uses liquid xenon as the sensitive target and is operated in two-phase (liquid/gas) mode, where the liquid level needs to be monitored and controlled in sub-millimeter precision. In this paper, we present a detailed design and study of two kinds of level meters for the PandaX dark matter detector. The long level meter is used to monitor the overall liquid level while short level meters are used to monitor the inclination of the detector. These level meters are cylindrical capacitors that are custom-made from two concentric metal tubes. Their capacitance values are read out by a universal transducer interface chip and are recorded by the PandaX slow control system. We present the developments that lead to level meters with long-term stability and sub-millimeter precision. Fluctuations (standard deviations) of less than 0.02 mm for the short level meters and less than 0.2 mm for the long level meter were achieved during a few days of test operation.

Development Of A Dual Phase Xenon Time Projection Chamber For Dark Matter Search

Tue, 15 Apr 2014 00:00:00 +0800

The cryogenic system for the Panda-X dark matter search experiment

Tue, 01 Jan 2013 00:00:00 +0800

Panda-X is a liquid xenon dual-phase detector for the Dark Matter Search. The first modestly-sized module will soon be installed in the China JinPing Deep Underground Laboratory in Sichuan province, P.R. China. The cryogenic system is designed to handle much larger detectors, even the final version in the ton scale. Special attention has been paid to the reliability, serviceability, and adaptability to the requirements of a growing experiment. The system is cooled by a single Iwatani PC150 Pulse Tube Refrigerator. After subtracting all thermal losses, the remaining cooling power is still 82 W. The fill speed was 0.75 g/s, but could be boosted by $LN_{2}$ assisted cooling to 3.3 g/s. For the continuous recirculation and purification through a hot getter, a heat exchanger was employed to reduce the required cooling power. The recirculation speed is limited to 2.9 g/s by the gas pump. At this speed, recirculation only adds 18.5 W to the heat load of the system, corresponding to a 95.2 % efficiency of the heat exchanger.

Publications - Talks

Mon, 01 Jan 0001 00:00:00 +0000

Remember Karl

Mon, 01 Jan 0001 00:00:00 +0000

In memory of our colleague, mentor, and friend

Karl Ludwig Giboni

1952–2025

Prof. Karl Ludwig Giboni earned his physics Ph.D. from RWTH Aachen, Germany, in 1981. He held postdoctoral positions at RWTH Aachen and Harvard University, contributing to the UA1 experiment at CERN, which led to the discovery of the W and Z bosons. After working in detector-related industry, he returned to academia with a fellowship from the Japanese Society for the Promotion of Science, then joined Columbia University as a Research Scientist in 1996. In 2010, he joined Shanghai Jiao Tong University as a Zhiyuan Chair Professor, where he worked until his retirement in 2022.

Scientific Publications

Mon, 01 Jan 0001 00:00:00 +0000

Scientific publications are maintained in INSPIRE-HEP and are no longer duplicated on this site.

Search for PandaX publications on INSPIRE-HEP

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