Search for Light Dark Matter with 259-day data in PandaX-4T

Abstract

We present a search for light dark matter particles through their interactions with atomic electrons and nucleons, utilizing PandaX-4T data with an effective exposure of 1.04 tonne$\cdot$year for ionization-only data and 1.20 tonne$\cdot$year for paired data. Our analysis focuses on the energy range (efficiency$>$0.01) of approximately 0.33 to 3 keV for nuclear recoils, and from 0.04 to 0.39 keV for electronic recoils. We establish the most stringent constraints on spin-independent dark matter-nucleon interactions within a mass range of 2.5 to 5.0 GeV/$c^2$, spin-dependent neutron-only interactions within 2.0 to 5.3 GeV/$c^2$, and spin-dependent proton-only interactions within 2.0 to 3.8 GeV/$c^2$. Their corresponding limits at 3\,GeV/$c^2$ are $1.1 \times 10^{-43}$, $1.6 \times 10^{-38}$, and $5.6 \times 10^{-37}$\,cm$^2$, respectively. Additionally, our results improve the upper limits on the dark matter-electron scattering cross-section by a factor of 1.5 and 9.3 for heavy and light mediator scenarios respectively within 50 MeV/$c^2$ to 10 GeV/$c^2$, compared with previous best results.

Figures (4)

• Figure 1: Top: the differential rates (in unit of events per metric ton per year per keV) of the DM scatterings off the target. The left shows the spectra for the LDM-nucleus scattering with LDM masses of 2 GeV (red) and 4 GeV (blue), assuming an LDM-nucleon cross section of 10$^{-40}$ cm$^2$. The spectra for the SI, proton-only SD, and neutron-only SD LDMs are shown in solid, dashed, and dotted lines, respectively. The right panel shows the spectra for LDM-electron scatterings with LDM masses of 50 MeV/$c^2$ (red) and 0.1 GeV (blue), assuming an LDM-electron cross section of 10$^{-37}$ cm$^2$. The solid and dashed lines represent the spectra for heavy and light mediator cases, respectively. All spectra are without efficiency applied. Middle: all components of the selection efficiency for the paired (solid) and US2 (dashed) data: green, data quality selection; blue, signal reconstruction; cyan, ROI; magenta, BDT; black, total. The gray shaded regions indicate $\pm$1$\sigma$ uncertainties. The efficiencies for the paired data are not shown in the right panel since they are not used in search of LDM-electron scattering. The efficiencies as a function of NR and ER energies are estimated based on the nominal charge yields shown in the bottom panels. Bottom: the charge (black) yields as a function of NR and ER energies are shown in the left and right panel, respectively. The solid lines show the nominal model with the shaded regions representing the $\pm$1$\sigma$ uncertainties. The black dashed lines in the right panel give the alternative yield model (P4-NEST) used in this work. The colored lines (blue, magenta, and green) give the best-fit charge yields in the LDM interpretations with different masses and model assumptions. No significant deviation from the nominal models is observed.
• Figure 2: Top panel: US2 data and fitted (for a LDM of 4 GeV/$c^2$) $S2$ spectra in number of electrons, run0 and run1 combined. The spectrum is stacked with best-fit contributions from the cathode (green), MD (yellow), $^8$B CE$\nu$NS (magenta), and LDM (red). The black error bars give the data distributions. Middle and bottom panels: the US2 data(black dots) distribution of the $S2$ width versus $S2$ charge. Along with expected 1$\sigma$ contours of 4 GeV/$c^2$ DM-nucleon spin-independent interaction(red dashed line), 2 GeV/$c^2$ DM-electron interaction via heavy mediator(blue dashed line), and light mediator(black dashed line), ${}^8$B solar neutrino(magenta shadow), MD background(yellow shadow), and cathode background(green shadow).
• Figure 3: The 90% CL exclusion limit(blue line) with 1$\sigma$ sensitivity(green band) on spin-independent DM-nucleon cross section(left panel), neutron-only(middle panel) and proton-only(right panel) spin-dependent DM-nucleon cross section, together with results from other work PandaX:2022xqxPandaX:2022aacXENON:2024hupXENON:2019gfnDarkSide:2018kukLUX:2016ggvPandaX-II:2018woaPICO:2019vsc.
• Figure 4: The 90% CL exclusion limit(blue line) with 1$\sigma$ sensitivity(green band) on DM-electron cross section via heavy(top panel) and light mediator(bottom panel) using constant-W model. The aggressive results using NEST light and charge yields are also overlaid(blue dashed line), as well as results of other experiments PandaX:2022xqxXENON:2019gfnDarkSide:2022knjadari2025firstaggarwal2025probing, and cosmological predictions from DM vector-portal freeze-in and freeze-out mechanisms Essig:2015cdabhattiprolu2024dark.