Recently, the PandaX Experiment (“Panda” Experiment) cooperation group led by Shanghai Jiao Tong University published the results of the PandaX-II Phase II experiment to find cosmic rays to accelerate light and dark matter in the form of an “editor’s recommendation” paper in the Form of “Editor’s Recommendation” paper. This is the first time that the data analysis of the dark matter direct detection experiment is carried out to find this signal, and it is also the first time that the PandaX experimental group has cooperated with domestic theoretical scholars to complete the whole chain research from the proposal of the ideal theory to the experimental detection.
Photo courtesy of cosmic ray (CR) accelerated light dark matter (DM) respondents
The signal probe used in the study was proposed in another collaborative article by Ge Shaofeng, a scholar of Li Zhengdao of Shanghai Jiao Tong University, Yuan Qiang, a researcher at the Purple Mountain Observatory of the Chinese Academy of Sciences, Zhou Ning, associate professor of the School of Physics and Astronomy of Shanghai Jiao Tong University, and Liu Jianglai, a professor at the School of Physics and Astronomy of Shanghai Jiao Tong University, in another collaborative article: Light and dark matter from the galactic cosmic ray acceleration, due to the rotation and shielding effect of the earth due to the rotation and shielding effect of the earth, the characteristics of stellar periodic modulation.
In recent years, the study of light and dark matter with a mass below GeV/c2 has attracted much attention, but because the mass is too light, the energy of the nuclear recoil signal generated is too low to be captured by the detector. However, as long as there is an interaction between dark matter and atomic nuclei, there must be a small part of light dark matter that is accelerated by the collision of high-energy protons and helium nuclei in the cosmic ray, thereby obtaining a high enough kinetic energy to produce an observable signal in the detector.
Due to the uneven distribution of dark matter and cosmic rays, the accelerated light dark matter is anisotropic, with the highest flow in the central direction of the Milky Way. Collision and scattering of high-speed light dark matter through the Earth and rock nuclei lose kinetic energy and deflect angles. Due to the earth’s continuous rotation, the net thickness of the rock layer through which the dark matter reaches the probe changes from 2.4 kilometers (the burial depth of Jinping Underground Laboratory) to more than 10,000 kilometers (the diameter of the earth), thus forming a unique stellar daily periodic modulation signal in the detector. The probe and the traditional direct detection of dark matter only rely on the interaction between dark matter and nucleons, so the model dependence is low, and the results have strong universality.
For this new type of stellar day modulation signal, the PandaX experimental group made a detailed Monte Carlo simulation of the process of dark matter passing through the rock into the Jinping Underground Laboratory, which completely included the effects of nuclear shape factor and angle deflection, and considered the scope of application of the elastic scattering process, and finally obtained a reliable earth shielding effect. The experimental team extracted the stellar time information of all the exposure data of pandax-II Phase II 580 kg of liquid xenon detection experiment in 400 days, and carried out a detailed search for the corresponding nuclear recoil signal region, using the number rate and energy spectrum with the distribution of the star time, and carried out a detailed search for the cosmic ray acceleration light and dark matter.
The experimental group gave strict restrictions on small mass dark matter and the respondent provided the picture
Thanks to the low radioactivity background and large exposure of the PandaX experiment, the experimental team gave strict restrictions on light and dark matter. The results show that the PandaX liquid xenon direct detection experiment can cover a large parameter space below the mass of GeV/c2, and exclude the scattering cross-sections of dark matter-nucleons in the orders of 10-31 cm2 and 10-28 cm2.
“This is the first restriction given by the Dark Matter Direct Detection Experiment Group to use cosmic rays to accelerate dark matter, beyond the restrictions of cosmological and astronomical observations on light dark matter.” Zhou Ning, one of the corresponding authors of the experimental article, told China Science Daily, “At present, the new generation of PandaX-4T four-ton liquid xenon detection experiments are in the process of intensively taking numbers, with a lower background level and higher detection sensitivity, which will further scan the parameter space of light and dark matter.” (Source: China Science Daily, Zhang Shuanghu, Huang Xin)
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