Experimental Limits on Solar Reflected Dark Matter with a New Approach on Accelerated-Dark-Matter–Electron Analysis in Semiconductors

Recently a dark matter–electron (DM–electron) paradigm has drawn much attention. Models beyond the standard halo model describing DM accelerated by high energy celestial bodies are under intense examination as well. In this Letter, a velocity components analysis (VCA) method dedicated to swift analysis of accelerated DM–electron interactions via semiconductor detectors is proposed and the first HPGe detector-based accelerated DM–electron analysis is realized. Utilizing the method, the first germanium based constraint on sub-GeV solar reflected DM–electron interaction is presented with the $205.4\mathrm{kg}·\mathrm{day}$ dataset from the CDEX-10 experiment. In the heavy mediator scenario, our result excels in the mass range of $5–15\mathrm{keV}/c^2$, achieving a 3 orders of magnitude improvement comparing with previous semiconductor experiments. In the light mediator scenario, the strongest laboratory constraint for DM lighter than $0.1\mathrm{MeV}/c^2$ is presented. The result proves the feasibility and demonstrates the vast potential of the VCA technique in future accelerated DM–electron analyses with semiconductor detectors.

Figure 1

Velocity components of isotropic DM velocity distribution. ${\mathit{v}}_{\mathrm{DM}}$ is DM particle’s velocity. ${\mathit{v}}_{\mathrm{E}}$ is the Earth’s velocity relative to the DM model, and for SHM it’s Earth’s velocity with respect to the Galactic rest frame. ${\mathit{v}}_{\mathrm{lab}}$ is the velocity seen by the lab. ${\mathit{v}}_{\max }$ is the maximum velocity of the model. ${\mathit{v}}_{\mathrm{DM}}={\mathit{v}}_{\mathrm{lab}}+{\mathit{v}}_{\mathrm{E}}$.

Figure 2

Reconstructed spectrum of the $\mathrm{c}\to \mathrm{f}$ process for $10\mathrm{GeV}/c^2$ DM from SHM in the heavy mediator scenario. The shaded area corresponds to the original result calculated by the exceed-dm package [56]. The blue and red lines are reconstructed results using the inverse square and uniform distribution. Solid lines from darker to dimmer represent the contributions of 11 velocity bins with bin width of $50\mathrm{km}/\mathrm{s}$ from $0–550\mathrm{km}/\mathrm{s}$ calculated by the modified exceed-dm package. The analysis threshold of CDEX-10 is represented by a black dashed line.

Figure 3

(a) SRDM flux distributions with different $m_{\chi }$ and ${\overline{\sigma }}_e$. SRDM flux in the light mediator scenario from Ref. [34] is depicted in dashed lines. Other lines correspond to the heavy mediator scenario, and results from Refs. [34] and [35] are consistent. The strips represent the binning of the velocity distributions. (b) Reconstructed HPGe detector response in the heavy mediator scenario to SRDM based on the distributions calculated by damascus-sun [60]. The detector’s resolution is determined by $35.8+16.6\times \sqrt{E}(\mathrm{eVee})$ [15], where $E$ is in keVee. Experimental data from CDEX-10 [15] after efficiency correction with known radioactive peaks removed and zoomed details in 0.16–2.16 keVee are also depicted. The bin width is 100 eVee.

Figure 4

$\chi \text{−}e$ constraints from the CDEX-10 experiment in the (a) heavy mediator and (b) light mediator scenario. The red solid and dashed lines correspond to the CDEX-10 results derived with the SRDM flux from Refs. [34] and [35], respectively. SRDM constraints from XENON1TS2 and $\mathrm{XENON}1\mathrm{TS}1+\mathrm{S}2$ presented by H. P. An et al. [34] (dotted lines), and those from CDMSHVeV, SENSEI, XENON10, and XENON1T presented by T. Emken et al. [35] (dash-dotted lines), are also depicted. The gray shaded regions correspond to the current SHM constraints from direct search experiments [23, 24, 25, 26, 27]. The brown shaded regions to the left are stellar cooling constraints from red giant (RG) stars for a dark photon-mediated model with ${\alpha }_D=0.5$ and $m_V=3m_{\chi }$, where $m_V$ is the dark photon mass and ${\alpha }_D=e_D^2/4\pi$, where $e_D$ is the gauge coupling in the dark sector [66].