https://pandax.sjtu.edu.cn/Publications/Recent content in Publications on PandaXHugoenFri, 22 Nov 2024 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/pandax-xt-a-deep-underground-multi-ten-tonne-liquid-xenon-observatory/Fri, 22 Nov 2024 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/pandax-xt-a-deep-underground-multi-ten-tonne-liquid-xenon-observatory/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.https://pandax.sjtu.edu.cn/publications/first-indication-of-solar-8-b-neutrinos-through-coherent-elastic-neutrino-nucleus-scatteri/Thu, 07 Nov 2024 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/first-indication-of-solar-8-b-neutrinos-through-coherent-elastic-neutrino-nucleus-scatteri/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.https://pandax.sjtu.edu.cn/publications/search-for-cosmic-ray-boosted-sub-mev-dark-matter-electron-scatterings-in-pandax-4t/Thu, 05 Sep 2024 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/search-for-cosmic-ray-boosted-sub-mev-dark-matter-electron-scatterings-in-pandax-4t/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.https://pandax.sjtu.edu.cn/publications/signal-response-model-in-pandax-4t/Fri, 19 Jul 2024 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/signal-response-model-in-pandax-4t/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.https://pandax.sjtu.edu.cn/publications/radon-removal-commissioning-of-the-pandax-4t-cryogenic-distillation-system/Mon, 08 Jul 2024 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/radon-removal-commissioning-of-the-pandax-4t-cryogenic-distillation-system/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.https://pandax.sjtu.edu.cn/publications/search-for-solar-pp-neutrinos-using-pandax-4t-electron-recoil-data/Sat, 15 Jun 2024 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/search-for-solar-pp-neutrinos-using-pandax-4t-electron-recoil-data/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.https://pandax.sjtu.edu.cn/publications/data-reduction-strategy-in-the-pandax-4t-experiment/Mon, 13 May 2024 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/data-reduction-strategy-in-the-pandax-4t-experiment/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.https://pandax.sjtu.edu.cn/publications/improvement-on-the-linearity-response-of-pandax-4t-with-new-photomultiplier-tubes-bases/Fri, 10 May 2024 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/improvement-on-the-linearity-response-of-pandax-4t-with-new-photomultiplier-tubes-bases/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.https://pandax.sjtu.edu.cn/publications/detecting-neutrinos-from-supernova-bursts-in-pandax-4t/Wed, 17 Apr 2024 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/detecting-neutrinos-from-supernova-bursts-in-pandax-4t/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.https://pandax.sjtu.edu.cn/publications/waveform-simulation-in-pandax-4t/Wed, 27 Mar 2024 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/waveform-simulation-in-pandax-4t/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.https://pandax.sjtu.edu.cn/publications/search-for-light-dark-matter-with-ionization-signals-in-the-pandax-4t-experiment/Tue, 27 Jun 2023 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/search-for-light-dark-matter-with-ionization-signals-in-the-pandax-4t-experiment/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.https://pandax.sjtu.edu.cn/publications/limits-on-the-luminance-of-dark-matter-from-xenon-recoil-data/Thu, 18 May 2023 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/limits-on-the-luminance-of-dark-matter-from-xenon-recoil-data/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.https://pandax.sjtu.edu.cn/publications/search-for-solar-8-b-neutrinos-in-the-pandax-4t-experiment-using-neutrino-nucleus-coherent/Wed, 11 Jan 2023 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/search-for-solar-8-b-neutrinos-in-the-pandax-4t-experiment-using-neutrino-nucleus-coherent/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 $GeV/c^2$.https://pandax.sjtu.edu.cn/publications/measurement-of-double-beta-decay-half-life-of-136xe-with-the-pandax-4t-detector/Tue, 25 Oct 2022 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/measurement-of-double-beta-decay-half-life-of-136xe-with-the-pandax-4t-detector/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.https://pandax.sjtu.edu.cn/publications/first-search-for-the-absorption-of-fermionic-dark-matter-with-the-pandax-4t-experiment/Thu, 13 Oct 2022 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/first-search-for-the-absorption-of-fermionic-dark-matter-with-the-pandax-4t-experiment/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.https://pandax.sjtu.edu.cn/publications/search-for-light-fermionic-dark-matter-absorption-on-electrons-in-pandax-4t/Thu, 13 Oct 2022 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/search-for-light-fermionic-dark-matter-absorption-on-electrons-in-pandax-4t/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.https://pandax.sjtu.edu.cn/publications/constraints-on-the-axial-vector-and-pseudo-scalar-mediated-wimp-nucleus-interactions-from/Mon, 03 Oct 2022 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/constraints-on-the-axial-vector-and-pseudo-scalar-mediated-wimp-nucleus-interactions-from/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.https://pandax.sjtu.edu.cn/publications/a-search-for-two-component-majorana-dark-matter-in-a-simplified-model-using-the-full-expos/Sat, 10 Sep 2022 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/a-search-for-two-component-majorana-dark-matter-in-a-simplified-model-using-the-full-expos/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.https://pandax.sjtu.edu.cn/publications/study-of-background-from-accidental-coincidence-signals-in-the-pandax-ii-experiment/Thu, 18 Aug 2022 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/study-of-background-from-accidental-coincidence-signals-in-the-pandax-ii-experiment/Study of background from accidental coincidence signals in the PandaX-II experimenthttps://pandax.sjtu.edu.cn/publications/neutron-induced-nuclear-recoil-background-in-the-pandax-4t-experiment/Fri, 29 Jul 2022 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/neutron-induced-nuclear-recoil-background-in-the-pandax-4t-experiment/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.https://pandax.sjtu.edu.cn/publications/low-radioactive-material-screening-and-background-control-for-the-pandax-4t-experiment/Mon, 27 Jun 2022 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/low-radioactive-material-screening-and-background-control-for-the-pandax-4t-experiment/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 $(2.https://pandax.sjtu.edu.cn/publications/search-for-cosmic-ray-boosted-sub-gev-dark-matter-at-the-pandax-ii-experiment/Wed, 27 Apr 2022 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/search-for-cosmic-ray-boosted-sub-gev-dark-matter-at-the-pandax-ii-experiment/We report a novel search for the cosmic-ray boosted dark matter using the 100 tonne · day full dataset of the PandaX-II detector located at the China Jinping Underground Laboratory. With the extra energy gained from the cosmic rays, sub-GeV dark matter particles can produce visible recoil signals in the detector. The diurnal modulations in rate and energy spectrum are utilized to further enhance the signal sensitivity. Our result excludes the dark matter–nucleon elastic scattering cross section between 10−31 and 10−28 cm2 for dark matter masses from 0.1 MeV/c2 to 0.1 GeV/c2, with a large parameter space previously unexplored by experimental collaborations.https://pandax.sjtu.edu.cn/publications/83-rb-83m-kr-production-and-cross-section-measurement-with-3-4-mev-and-20-mev-proton-beams/Wed, 05 Jan 2022 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/83-rb-83m-kr-production-and-cross-section-measurement-with-3-4-mev-and-20-mev-proton-beams/${}^{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.https://pandax.sjtu.edu.cn/publications/light-yield-and-field-dependence-measurement-in-pandax-ii-dual-phase-xenon-detector/Wed, 05 Jan 2022 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/light-yield-and-field-dependence-measurement-in-pandax-ii-dual-phase-xenon-detector/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.https://pandax.sjtu.edu.cn/publications/dark-matter-search-results-from-the-pandax-4t-commissioning-run/Thu, 23 Dec 2021 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/dark-matter-search-results-from-the-pandax-4t-commissioning-run/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 $GeV/c^2$.https://pandax.sjtu.edu.cn/publications/pandax-4t-cryogenic-distillation-system-for-removing-krypton-from-xenon/Mon, 20 Dec 2021 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/pandax-4t-cryogenic-distillation-system-for-removing-krypton-from-xenon/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.https://pandax.sjtu.edu.cn/publications/a-500-ms-s-waveform-digitizer-for-pandax-dark-matter-experiments/Fri, 10 Dec 2021 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/a-500-ms-s-waveform-digitizer-for-pandax-dark-matter-experiments/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.https://pandax.sjtu.edu.cn/publications/performance-of-cryogenic-demountable-indium-seal-at-high-pressures/Mon, 13 Sep 2021 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/performance-of-cryogenic-demountable-indium-seal-at-high-pressures/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.https://pandax.sjtu.edu.cn/publications/bamboomc-a-geant4-based-simulation-program-for-the-pandax-experiments/Wed, 25 Aug 2021 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/bamboomc-a-geant4-based-simulation-program-for-the-pandax-experiments/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.https://pandax.sjtu.edu.cn/publications/constraining-self-interacting-dark-matter-with-the-full-dataset-of-pandax-ii/Wed, 11 Aug 2021 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/constraining-self-interacting-dark-matter-with-the-full-dataset-of-pandax-ii/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.https://pandax.sjtu.edu.cn/publications/design-and-commissioning-of-the-pandax-4t-cryogenic-distillation-system-for-krypton-and-ra/Fri, 23 Jul 2021 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/design-and-commissioning-of-the-pandax-4t-cryogenic-distillation-system-for-krypton-and-ra/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.https://pandax.sjtu.edu.cn/publications/the-cryogenics-and-xenon-handling-system-for-the-pandax-4t-experiment/Sat, 05 Jun 2021 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/the-cryogenics-and-xenon-handling-system-for-the-pandax-4t-experiment/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.https://pandax.sjtu.edu.cn/publications/search-for-light-dark-matter-electron-scatterings-in-the-pandax-ii-experiment/Fri, 28 May 2021 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/search-for-light-dark-matter-electron-scatterings-in-the-pandax-ii-experiment/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.https://pandax.sjtu.edu.cn/publications/determination-of-responses-of-liquid-xenon-to-low-energy-electron-and-nuclear-recoils-usin/Wed, 21 Apr 2021 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/determination-of-responses-of-liquid-xenon-to-low-energy-electron-and-nuclear-recoils-usin/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.https://pandax.sjtu.edu.cn/publications/diurnal-effect-of-sub-gev-dark-matter-boosted-by-cosmic-rays/Fri, 05 Mar 2021 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/diurnal-effect-of-sub-gev-dark-matter-boosted-by-cosmic-rays/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.https://pandax.sjtu.edu.cn/publications/internal-calibration-of-the-pandax-ii-detector-with-radon-gaseous-sources/Thu, 31 Dec 2020 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/internal-calibration-of-the-pandax-ii-detector-with-radon-gaseous-sources/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.https://pandax.sjtu.edu.cn/publications/an-improved-design-of-the-readout-base-board-of-the-photomultiplier-tube-for-future-pandax/Sun, 06 Dec 2020 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/an-improved-design-of-the-readout-base-board-of-the-photomultiplier-tube-for-future-pandax/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.https://pandax.sjtu.edu.cn/publications/a-search-for-solar-axions-and-anomalous-neutrino-magnetic-moment-with-the-complete-pandax/Thu, 27 Aug 2020 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/a-search-for-solar-axions-and-anomalous-neutrino-magnetic-moment-with-the-complete-pandax/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.https://pandax.sjtu.edu.cn/publications/results-of-dark-matter-search-using-the-full-pandax-ii-exposure/Thu, 27 Aug 2020 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/results-of-dark-matter-search-using-the-full-pandax-ii-exposure/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 $GeV / c^{2}$.https://pandax.sjtu.edu.cn/publications/an-improved-evaluation-of-the-neutron-background-in-the-pandax-ii-experiment/Sat, 09 Nov 2019 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/an-improved-evaluation-of-the-neutron-background-in-the-pandax-ii-experiment/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.https://pandax.sjtu.edu.cn/publications/searching-for-neutrino-less-double-beta-decay-of-136xe-with-pandax-ii-liquid-xenon-detecto/Mon, 16 Sep 2019 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/searching-for-neutrino-less-double-beta-decay-of-136xe-with-pandax-ii-liquid-xenon-detecto/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.https://pandax.sjtu.edu.cn/publications/dark-matter-direct-search-sensitivity-of-the-pandax-4t-experiment/Fri, 17 Aug 2018 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/dark-matter-direct-search-sensitivity-of-the-pandax-4t-experiment/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 $GeV/c^{2}$.https://pandax.sjtu.edu.cn/publications/signal-background-discrimination-with-convolutional-neural-networks-in-the-pandax-iii-expe/Thu, 09 Aug 2018 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/signal-background-discrimination-with-convolutional-neural-networks-in-the-pandax-iii-expe/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.https://pandax.sjtu.edu.cn/publications/constraining-dark-matter-models-with-a-light-mediator-at-the-pandax-ii-experiment/Thu, 12 Jul 2018 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/constraining-dark-matter-models-with-a-light-mediator-at-the-pandax-ii-experiment/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.https://pandax.sjtu.edu.cn/publications/pandax-ii-constraints-on-spin-dependent-wimp-nucleon-effective-interactions/Thu, 05 Jul 2018 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/pandax-ii-constraints-on-spin-dependent-wimp-nucleon-effective-interactions/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 $M_{WIMP} > 40 GeV/c^2$.https://pandax.sjtu.edu.cn/publications/design-and-commissioning-of-a-600-l-time-projection-chamber-with-microbulk-micromegas/Fri, 01 Jun 2018 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/design-and-commissioning-of-a-600-l-time-projection-chamber-with-microbulk-micromegas/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.https://pandax.sjtu.edu.cn/publications/exploring-the-dark-matter-inelastic-frontier-with-79-6-days-of-pandax-ii-data/Tue, 28 Nov 2017 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/exploring-the-dark-matter-inelastic-frontier-with-79-6-days-of-pandax-ii-data/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 $10 TeV/c^{2}$.https://pandax.sjtu.edu.cn/publications/limits-on-axion-couplings-from-the-first-80-days-of-data-of-the-pandax-ii-experiment/Wed, 01 Nov 2017 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/limits-on-axion-couplings-from-the-first-80-days-of-data-of-the-pandax-ii-experiment/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.https://pandax.sjtu.edu.cn/publications/dark-matter-results-from-54-ton-day-exposure-of-pandax-ii-experiment/Mon, 30 Oct 2017 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/dark-matter-results-from-54-ton-day-exposure-of-pandax-ii-experiment/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.https://pandax.sjtu.edu.cn/publications/update-of-the-trigger-system-of-the-pandax-ii-experiment/Fri, 25 Aug 2017 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/update-of-the-trigger-system-of-the-pandax-ii-experiment/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.https://pandax.sjtu.edu.cn/publications/first-dark-matter-search-results-from-the-pandax-i-experiment/Wed, 07 Jun 2017 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/first-dark-matter-search-results-from-the-pandax-i-experiment/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.https://pandax.sjtu.edu.cn/publications/current-status-of-direct-dark-matter-detection-experiments/Thu, 02 Mar 2017 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/current-status-of-direct-dark-matter-detection-experiments/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.https://pandax.sjtu.edu.cn/publications/spin-dependent-weakly-interacting-massive-particle-nucleon-cross-section-limits-from-first/Wed, 01 Feb 2017 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/spin-dependent-weakly-interacting-massive-particle-nucleon-cross-section-limits-from-first/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.https://pandax.sjtu.edu.cn/publications/krypton-and-radon-background-in-the-pandax-i-dark-matter-experiment/Sun, 01 Jan 2017 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/krypton-and-radon-background-in-the-pandax-i-dark-matter-experiment/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.https://pandax.sjtu.edu.cn/publications/material-screening-with-hpge-counting-station-for-pandax-experiment/Fri, 01 Jul 2016 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/material-screening-with-hpge-counting-station-for-pandax-experiment/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.https://pandax.sjtu.edu.cn/publications/dark-matter-search-results-from-the-commissioning-run-of-pandax-ii/Tue, 21 Jun 2016 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/dark-matter-search-results-from-the-commissioning-run-of-pandax-ii/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 $44.7$ $GeV/c^2$.https://pandax.sjtu.edu.cn/publications/dark-matter-results-from-first-98-7-days-of-data-from-the-pandax-ii-experiment/Fri, 03 Jun 2016 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/dark-matter-results-from-first-98-7-days-of-data-from-the-pandax-ii-experiment/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.https://pandax.sjtu.edu.cn/publications/the-electronics-and-data-acquisition-system-for-the-pandax-i-dark-matter-experiment/Thu, 02 Jun 2016 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/the-electronics-and-data-acquisition-system-for-the-pandax-i-dark-matter-experiment/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.https://pandax.sjtu.edu.cn/publications/performance-of-photosensors-in-the-pandax-i-experiment/Wed, 01 Jun 2016 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/performance-of-photosensors-in-the-pandax-i-experiment/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.https://pandax.sjtu.edu.cn/publications/low-mass-dark-matter-search-results-from-full-exposure-of-the-pandax-i-experiment/Mon, 01 Jun 2015 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/low-mass-dark-matter-search-results-from-full-exposure-of-the-pandax-i-experiment/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.https://pandax.sjtu.edu.cn/publications/pandax-a-liquid-xenon-dark-matter-experiment-at-cjpl/Tue, 03 Jun 2014 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/pandax-a-liquid-xenon-dark-matter-experiment-at-cjpl/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.https://pandax.sjtu.edu.cn/publications/development-of-the-liquid-level-meters-for-the-pandax-dark-matter-detector/Sun, 01 Jun 2014 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/development-of-the-liquid-level-meters-for-the-pandax-dark-matter-detector/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.https://pandax.sjtu.edu.cn/publications/the-cryogenic-system-for-the-panda-x-dark-matter-search-experiment/Tue, 01 Jan 2013 00:00:00 +0800https://pandax.sjtu.edu.cn/publications/the-cryogenic-system-for-the-panda-x-dark-matter-search-experiment/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.