Search for Solar ${}^8\mathrm{B}$ Neutrinos in the PandaX-4T Experiment Using Neutrino-Nucleus Coherent Scattering

A search for interactions from solar ${}^8\mathrm{B}$ neutrinos elastically scattering off xenon nuclei using PandaX-4T commissioning data is reported. The energy threshold of this search is further lowered compared with the previous search for dark matter, with various techniques utilized to suppress the background that emerges from data with the lowered threshold. A blind analysis is performed on the data with an effective exposure of $0.48\mathrm{tonne}\mathrm{year}$, and no significant excess of events is observed. Among the results obtained using the neutrino-nucleus coherent scattering, our results give the best constraint on the solar ${}^8\mathrm{B}$ neutrino flux. We further provide a more stringent limit on the cross section between dark matter and nucleon in the mass range from 3 to $9\mathrm{GeV}/{\mathrm{c}}^2$.

Figure 1

Total efficiency (red solid line) to the solar ${}^8\mathrm{B}$ neutrino $\mathrm{CE}\nu \mathrm{NS}$ in this analysis with the number of $S1$ hits to be 2 or 3. The blue, green, cyan, and magenta solid lines represent the signal efficiencies due to the signal reconstruction, data selection, ROI, and BDT, respectively. The signal efficiency in the previous study [10] is also given in the pink dashed line as a reference. The ideal spectra of the solar ${}^8\mathrm{B}$ $\mathrm{CE}\nu \mathrm{NS}$ and the DM-nucleus interaction with the DM mass of $4(8)\mathrm{GeV}/{\mathrm{c}}^2$ with an assumed DM-nucleon cross section of ${10}^{-44}{\mathrm{cm}}^2$ are overlaid as well in the black solid and gray dashed (dotted) curves, respectively, with the scale indicated on the right axis.

Figure 2

Comparison between the light (top panel) and charge (bottom panel) yields used in this analysis (in the solid black lines) with the nominal NEST v2.3.6 [19] (dashed black lines) and other measurements taken at different drift electric fields [21, 22, 23, 24]. The $1\sigma$ uncertainty from Ref. [20] for the light and charge yields are shown in the gray bands.

Figure 3

The $S1$ (left panels) and $S2$ (right panels) spectra in the sideband (top panels) and ROI (bottom panels) for the 2-hit data, with the data and corresponding predictions overlaid. The shaded regions represent the $1\sigma$ uncertainty of the prediction (30%). We also overlay the expected ${}^8\mathrm{B}$ $\mathrm{CE}\nu \mathrm{NS}$ spectra (scaled up by 50) in the bottom panels, shown in blue solid lines. The goodness-of-fit $p$ values of the $S1$ and $S2$ spectra in the sideband and ROI are all no less than 0.1.

Figure 4

Top panel: our constraint on the solar neutrino flux using the $\mathrm{CE}\nu \mathrm{NS}$ analysis, along with the XENON1T results [6] using the same detection channel and the B16-GS98 standard solar model prediction [29]. Bottom panel: updated constraints on the DM-nucleon spin-independent cross section. The red solid and dashed lines represent the PandaX-4T results from this and the previous searches [10], respectively. The black solid and dashed lines represent the results from XENON1T with and without optimization in the low-energy region [6, 30]. Several results from other experiments [31, 32] are also shown. The neutrino floors (probability for an ideal xenon detector to see less-than-$3\sigma$-significance DM signal) [18] under different exposure assumptions (1, 10, and $1000\mathrm{tonne}\text{−}\mathrm{year}$ from top to bottom) are shown in the gray shaded regions. The green region represents the $\pm 1\sigma$ sensitivity band for the DM search.

Figure 5

The comparisons between the neutron calibration data and WS of $S1$ width (top), ${\sigma }_{\mathrm{pos}}$ (middle), and $S2$ width (bottom) normalized distributions in the ROI.

Figure 6

Comparison between the ${\mathcal{F}}_{S2}$ distributions from the WS (red solid line) and data (black dots with error bars).