Progress review on the dark matter direct detection experiments

Subject Code:A05 A progress review article on the dark matter direct detection experiments,authored by Prof.Liu Jianglai(刘江来),Dr.Chen Xun(谌勋)and Prof.Ji Xiangdong(季向东,corresponding author)from the Shanghai Jiao Tong University,was published online in Nature Physics(2017,13:212—216)recently.

Probing inelastic signatures of dark matter detection via polarized nucleus

We investigate the inelastic signatures of dark matter-nucleus interactions,explicitly focusing on the ramifications of polarization,dark matter splitting,and the Migdal effect.Direct detection experiments,crucial for testing the existence of dark matter,encounter formidable obstacles,such as indomitable neutrino backgrounds and elusive determination of dark matter spin.To overcome these challenges,we explore the potential of polarized-target dark matter scattering,examining the impact of nonvanishing mass splitting,and the role of the Migdal effect in detecting dark matter.Our analysis demonstrates the valuable utility of the polarized triple-differential event rate as an effective tool for examining inelastic dark matter.It enables us to investigate angular and energy dependencies,providing valuable insights into the scattering process.

Interpretation of XENON1T excess with MeV boosted dark matter

The XENON IT excess of keV electron recoil events may be induced by the scattering of electrons and long-lived particles with an MeV mass and high speed.We consider a tangible model composed of two scalar MeV dark matter(DM) particles,S_(A) and S_(B),to interpret the XENON IT keV excess via boosted S_(B).A small mass splitting m_(S_(A))-m_(S_(B))>0 is introduced,and the boosted S_(B) can be produced using the dark annihilation process of S_(A)S_(A)^(■)→φ→S_(B)S_(B)^(■) via a resonant scalar φ.S_(B)-electron scattering is intermediated by a vector boson X.Although the constraints from Big Bang nucleosynthesis,cosmic microwave background(CMB),and low-energy experiments set the X-mediated S_(B)-electron scattering cross section to be≤10^(-35)cm^(2),the MeV scale DM with a resonance enhanced dark annihilation today can still provide sufficient boosted S_(B) and induce the XENON1 T keV excess.The relic density of S_(B) is significantly reduced by the s-wave process S_(B)S_(B)^(■)→XX,which is permitted by the constraints from CMB and 21-cm absorption.A very small relic fraction of S_(B) is compatible with the stringent bounds on un-boosted S_(B)-electron scattering in DM direct detection,and the S_(A)-electron scattering is also allowed.