Nature. 2018 Dec;564(7734):83-86. doi: 10.1038/s41586-018-0739-1. Epub 2018 Dec 5.
Observations of galaxies and primordial radiation suggest that the Universe is made mostly of non-luminous dark matter. Several new types of fundamental particle have been proposed as candidates for dark matter, such as weakly interacting massive particles (WIMPs). These particles would be expected to interact with nuclei in suitable detector materials on Earth, for example, causing them to recoil. However, no definitive signal from such dark-matter interactions has been detected despite concerted efforts by many collaborations. One exception is the much-debated claim by the DAMA collaboration of a statistically significant (more than nine standard deviations) annual modulation in the rate of nuclear interaction events. Annual modulation is expected because of the variation in Earth's velocity relative to the Galaxy's dark-matter halo that arises from Earth's orbital motion around the Sun. DAMA observed a modulation in the rate of interaction events in their detector with a period and phase consistent with that expected for WIMPs. Several groups have been working to develop experiments with the aim of reproducing DAMA's results using the same target medium (sodium iodide). To determine whether there is evidence for an excess of events above the expected background in sodium iodide and to look for evidence of an annual modulation, the COSINE-100 experiment uses sodium iodide as the target medium to carry out a model-independent test of DAMA's claim. Here we report results from the initial operation of the COSINE-100 experiment related to the first task. We observe no excess of signal-like events above the expected background in the first 59.5 days of data from COSINE-100. Assuming the so-called standard dark-matter halo model, this result rules out spin-independent [corrected] WIMP-nucleon interactions as the cause of the annual modulation observed by the DAMA collaboration.. The exclusion limit on the WIMP-sodium interaction cross-section is 1.14 × 10 cm for 10-GeV c WIMPs at a 90% confidence level. The COSINE-100 experiment will continue to collect data for two more years, enabling a model-independent test of the annual modulation observed by the DAMA collaboration.
对星系和原初辐射的观测表明，宇宙主要由不发光的暗物质构成。已经提出了几种新型基本粒子作为暗物质的候选者，比如弱相互作用大质量粒子（WIMP）。预计这些粒子会与地球上合适的探测器材料中的原子核相互作用，例如使原子核产生反冲。然而，尽管许多合作团队共同努力，仍未检测到来自此类暗物质相互作用的确切信号。一个例外是DAMA合作团队备受争议的宣称，即核相互作用事件率存在具有统计学显著性（超过九个标准差）的年度调制。由于地球绕太阳公转导致地球相对于银河系暗物质晕的速度变化，所以预计会出现年度调制。DAMA在其探测器中观测到相互作用事件率的调制，其周期和相位与WIMP预期的一致。几个团队一直在致力于开展实验，目的是使用相同的靶介质（碘化钠）重现DAMA的结果。为了确定碘化钠中是否存在超出预期本底的事件证据，并寻找年度调制的证据，COSINE - 100实验使用碘化钠作为靶介质，对DAMA的宣称进行与模型无关的检验。在此，我们报告COSINE - 100实验初始运行与第一项任务相关的结果。在COSINE - 100实验最初59.5天的数据中，我们未观测到超出预期本底的类信号事件。假设所谓的标准暗物质晕模型，该结果排除了自旋无关[修正后]的WIMP - 核子相互作用是DAMA合作团队观测到的年度调制的原因。对于10 GeV c的WIMP，在90%置信水平下，WIMP - 钠相互作用截面的排除极限为1.14×10⁻⁴⁴ cm²。COSINE - 100实验将继续收集另外两年的数据，从而能够对DAMA合作团队观测到的年度调制进行与模型无关的检验。
