New results on the detection of axions and galaxy axion-like particles(ALPs) with 80 day of PandaX-II data were published online in Physical Review Letters on Nov 1, 2017 (on the same issue with another PandaX-II paper on 54 ton-day WIMP search results). No positive signal was found by the most sensitive detector all over the world, so that the most stringent constraints on the properties of axion and ALPs were set.
Axion is a new type of particle which was proposed by Steven Weinberg and Frank Wilczek in late 1970s to explain the CP conservation in strong interactions. It is also one of the top candidates of dark matter particles in our universe. 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, experimentalist may determine the mass and coupling constant of axions with electrons.
PandaX-II is one of the largest running dark matter direct detection experiment. It uses high purity xenon as the detection medium. The PandaX-II detector is sensitive in the searching of rare events within the energy region around several keV. In this analysis, PandaX-II obtained the world leading results with about 80 days of data. The upper limit on the coupling between the solar axion and electron was set to be less than $4.35\times10^{-12}$ when the axion mass is smaller than 1 keV. The limit on that of galactic ALPs is on the order of $1\times10^{-13}$, for ALPs in the mass range of 1-10 keV.
This paper is the fourth letter published in Physical Review Letters from PandaX-II. More exciting results are expected as PandaX-II is accumulating more exposure.
PandaX-II合作组发表轴子探测结果
2017年11月1日，《物理评论快报》在线发表了上海交大牵头的PandaX-II实验在轴子（axion）探测方面的最新结果 (同一期的《快报》也发表了PandaX-II 54吨天的WIMP暗物质探测结果)。实验未发现轴子的踪迹，从而进一步压缩了轴子所可能存在的参数空间。
轴子是理论物理学家为了合理解释强相互作用中CP守恒而提出的一种玻色子。同时轴子及一些类轴子粒子（axion-like partiles, ALP）也能作为暗物质的一种候选粒子，因此目前国际上有很多合作组正在进行轴子的搜索。根据理论预测，轴子可能存在与电子的耦合，从而能够将自己的全部能量转移给电子。实验物理学家通过测量这些意外获得能量的电子的信息，便能够确定轴子的质量和同电子的耦合常数。
PandaX-II是目前世界上正在运行的最大的地下暗物质探测实验之一，实验采用高纯氙为探测介质，在千电子伏特能区的稀有事例的探测上具有极高的灵敏度。在这次的数据分析当中，PandaX-II采用了大约80天的数据量就获得了国际同类实验中最为领先的结果。该结果将千电子伏能量区域内，来自太阳的轴子与电子间的耦合常数限制在小于$4.35\times10^{-12}$的范围内，而星际类轴子粒子的耦合常数则限制在$1\times10^{-13}$以下。
这是PandaX-II实验第四篇发表在《物理评论快报》上的文章。随着实验的继续运行，PandaX合作组将积累更多的数据，取得更多的成果。
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