暗物质粒子探测卫星研究进展

Research progress of Dark Matter Particle Explorer

天文观测表明,宇宙中广泛存在暗物质,其丰度是普通物质的5倍,占宇宙总能量份额的约1/4.自20世纪30年代天文学家通过引力观测发现暗物质以来,经过近百年的探索,其物理本质至今仍然不为我们所知.另一个世纪谜题是高能宇宙射线的起源、加速和传播.暗物质的本质和宇宙射线的起源位列美国国家研究委员会(National Research Council)遴选出的21世纪11个宇宙物理学重大科学问题之列.探测暗物质粒子也是世界各国竞争异常激烈的科技热点.我国发射的暗物质粒子探测卫星,其主要的科学目标即通过精确观测高能宇宙射线电子和伽马射线来间接探测暗物质粒子.作为一个高能粒子探测器,暗物质粒子探测卫星观测数据也可用于宇宙射线物理和相关天体物理研究.基于暗物质粒子探测卫星的数据,我们得到了对宇宙射线电子和质子能谱的最为精确的测量,揭示了能谱上的新结构,为限制暗物质粒子属性和理解宇宙射线起源提供了重要数据.暗物质粒子探测卫星还探测到约250个伽马射线点源以及银河系弥散伽马射线辐射.本文综述了暗物质粒子探测卫星的设计、运行和数据分析进展.

Quite a lot of astronomical and cosmological observations reveal that dark matter widely exists in our Universe. It occupies nearly 1/4 of the total energy budget of the Universe, and is about 5 times more abundant than the normal matter. The nature of dark matter is one of the most important fundamental questions of modern physics and astronomy. To probe dark matter particles is also highly competitive among many countries around the world. China has launched the Dark Matter Particle Explorer(DAMPE;also known as "Wukong") to indirectly detect dark matter via high-precision observations of highenergy electrons and gamma-rays. As a high-energy particle detector, the DAMPE data can also be useful for probing the origin and propagation of cosmic rays, which is another century-long problem, and the energetic activities of extreme objects such as black holes and neutron stars. DAMPE has the highest energy resolution for electron and gamma-ray measurements, and the highest electron-proton discrimination capability above Te V energies. Using the data recorded by DAMPE, we obtain by far the most precise measurements of the spectra of cosmic ray electrons and protons, and reveal new spectral features which were not discovered or clarified before. For the total electron plus positron spectrum, the DAMPE result covers an energy range of 25 GeV-4.6 TeV, which reaches the highest energy among all the space direct detections. A spectral hardening around 50 GeV, and a softening around 0.9 TeV have been revealed by DAMPE. Some hint of fine structures of the spectrum is also shown which requires more data for confirmation or exclusion. The spectral features of the DAMPE electron plus positron spectrum have very interesting and important implications on the origin and distribution of high-energy electron sources. Particularly, the 0.9 TeV break may reveal the fact that sources of Te V electrons distribute discretely in the Galaxy. The energy range coverage of the DAMPE proton spectrum is from 40 GeV to 100 TeV. For the first time, DAMPE measures the proton spectrum up to 100 TeV with a high statistics. Besides the hundreds of Ge V spectral hardening, the DAMPE measurement further reveals a clear spectral softening around 14 TeV.The softening feature of the proton spectrum may be an imprint of nearby cosmic ray acceleration sources. Alternatively,the spectral structures of protons may be due to the superposition of multiple source populations. High-energy gamma-rays have also been robustly identified from the DAMPE data. The analysis shows the detection of luminous diffuse emission from the Galactic plane and nearly 250 pointlike sources in the gamma-ray sky, most of which are active galactic nuclei and pulsars. The DAMPE results offer important data in constraining/understanding the properties of dark matter and cosmic rays. We review the design, operation and data analysis of DAMPE in this work, with a focus on the analyses of spectra of cosmic ray electrons and protons.