Z. H. Zhang

Dark matter direct detection experiments mostly operate at deep underground laboratories. It is necessary to consider shielding effect of the Earth, especially for dark matter particles interacting with a large cross section. We analyzed and simulated the Earth shielding effect for dark matter at the China Jinping Underground Laboratory (CJPL) with a simulation package, CJPL Earth Shielding Simulation code (CJPL_ESS), which is applicable to other underground locations. The further constraints on the $\ensuremath{\chi}\text{\ensuremath{-}}\mathrm{N}$ cross section exclusion regions are derived based on the studies with CDEX experiment data.

A search for exotic dark matter (DM) in the sub-GeV mass range has been conducted using 205 kg day data taken from a p-type point contact germanium detector of the CDEX-10 experiment at China's Jinping underground laboratory. New low-mass dark matter searching channels, neutral current fermionic DM absorption (χ+A→ν+A) and DM-nucleus 3→2 scattering (χ+χ+A→ϕ+A), have been analyzed with an energy threshold of 160 eVee. No significant signal was found; thus new limits on the DM-nucleon interaction cross section are set for both models at the sub-GeV DM mass region. A cross section limit for the fermionic DM absorption is set to be 2.5×10^{-46} cm^{2} (90% C.L.) at DM mass of 10 MeV/c^{2}. For the DM-nucleus 3→2 scattering scenario, limits are extended to DM mass of 5 and 14 MeV/c^{2} for the massless dark photon and bound DM final state, respectively.

We present novel constraints on boosted light dark matter particles (denoted as ``$\ensuremath{\chi}$'') from evaporating primordial black holes (PBHs) using $205.4\text{ }\text{ }\mathrm{kg}\ifmmode\cdot\else\textperiodcentered\fi{}\mathrm{day}$ data from the China Jinping Underground Laboratory's CDEX-10 p-type point contact germanium detector with a 160 eVee analysis threshold. $\ensuremath{\chi}$ from PBHs with masses ranging from $1\ifmmode\times\else\texttimes\fi{}{10}^{15}\text{ }\text{ }\mathrm{g}$ to $7\ifmmode\times\else\texttimes\fi{}{10}^{16}\text{ }\text{ }\mathrm{g}$ are searched in this work. In the presence of PBH abundance compatible with present bounds, our result excludes the $\ensuremath{\chi}$-nucleon elastic-scattering cross section region from $3.4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}32}\text{ }\text{ }{\mathrm{cm}}^{2}$ to $2.3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}29}\text{ }\text{ }{\mathrm{cm}}^{2}$ for $\ensuremath{\chi}$ of 1 keV to 24 MeV from PBHs with masses of $5\ifmmode\times\else\texttimes\fi{}{10}^{15}\text{ }\text{ }\mathrm{g}$, as well as from $1.1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}28}\text{ }\text{ }{\mathrm{cm}}^{2}$ to $7.6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}28}\text{ }\text{ }{\mathrm{cm}}^{2}$ for $\ensuremath{\chi}$ of 1 keV to 0.6 MeV from PBHs with masses of $7\ifmmode\times\else\texttimes\fi{}{10}^{16}\text{ }\text{ }\mathrm{g}$. If the $\ensuremath{\chi}$-nucleon elastic-scattering cross section can be determined in the future, the abundance of PBHs may be severely constrained by $\ensuremath{\chi}$ evaporation. With the lower threshold (160 eVee) of the CDEX-10 experiment compared to the previously used experiments, this work allows for a better reach at soft spectra produced by heavier PBHs, which demonstrates the vast potential of such a technical route to pursue $\ensuremath{\chi}$ from larger PBHs with a low threshold.

A natural broad energy germanium detector is operated in the China Jinping Underground Laboratory for a feasibility study of building the next generation experiment of the neutrinoless double-beta ($0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$) decay of $^{76}\mathrm{Ge}$. The setup of the prototype facility, characteristics of the broad energy germanium detector, background reduction methods, and data analysis are described in this paper. A background index of $6.4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}\text{ }\text{ }\mathrm{counts}/(\mathrm{keV}\text{ }\mathrm{kg}\text{ }\mathrm{day})$ is achieved and 1.86 times lower than our previous result of the CDEX-1 detector. No signal is observed with an exposure of 186.4 kg day, thus a limit on the half life of $^{76}\mathrm{Ge}$ $0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$ decay is set at ${\mathrm{T}}_{1/2}^{0\ensuremath{\nu}}>5.62\ifmmode\times\else\texttimes\fi{}{10}^{22}\text{ }\text{ }\mathrm{yr}$ at 90% C.L. The limit corresponds to an effective Majorana neutrino mass in the range of 4.6--10.3 eV, dependent on the nuclear matrix elements.

We investigate exotic neutrino interactions using the $205.4\text{\ensuremath{-}}\mathrm{kg}\ifmmode\cdot\else\textperiodcentered\fi{}\mathrm{day}$ dataset from the CDEX-10 experiment at the China Jinping Underground Laboratory. New constraints on the mass and couplings of new gauge bosons are presented. Two nonstandard neutrino interactions are considered: a $U(1{)}_{\mathrm{B}--\mathrm{L}}$ gauge-boson-induced interaction between an active neutrino and electron/nucleus, and a dark-photon-induced interaction between a sterile neutrino and electron/nucleus via kinetic mixing with a photon. This work probes an unexplored parameter space involving sterile neutrino coupling with a dark photon. New laboratory limits are derived on dark photon masses below $1\text{ }\text{ }\mathrm{eV}/{c}^{2}$ at some benchmark values of $\mathrm{\ensuremath{\Delta}}{m}_{41}^{2}$ and ${g}^{\ensuremath{'}2}{\mathrm{sin}}^{2}2{\ensuremath{\theta}}_{14}$.