First Indication of Solar $^8$B Neutrino Flux through Coherent Elastic Neutrino-Nucleus Scattering in PandaX-4T

TL;DR

This paper reports the first detection of solar $^8$B neutrino flux via coherent elastic neutrino-nucleus scattering using the PandaX-4T detector, providing a novel measurement consistent with solar model predictions.

Contribution

It presents the first indication of solar $^8$B neutrino flux through coherent scattering in a dark matter detector, combining multiple data samples for the measurement.

Findings

Detected a $^8$B neutrino flux of (8.4±3.1)×10^6 cm^-2 s^-1

Disfavored background-only hypothesis at 2.64σ significance

First observation of solar $^8$B neutrino 'fog' in dark matter detection

Abstract

The PandaX-4T liquid xenon detector at the China Jinping Underground Laboratory is used to measure the solar $^8$B neutrino flux by detecting neutrinos through coherent scattering with xenon nuclei. Data samples requiring the coincidence of scintillation and ionization signals (paired), as well as unpaired ionization-only signals (US2), are selected with energy threshold of approximately 1.1 keV (0.33 keV) nuclear recoil energy. Combining the commissioning run and the first science run of PandaX-4T, a total exposure of 1.20 and 1.04 tonne$\cdot$year are collected for the paired and US2, respectively. After unblinding, 3 and 332 events are observed with an expectation of 2.8$\pm$0.5 and 251$\pm$32 background events, for the paired and US2 data, respectively. A combined analysis yields a best-fit $^8$B neutrino signal of 3.5 (75) events from the paired (US2) data sample, with $\sim$37\% uncertainty, and the background-only hypothesis is disfavored at 2.64$\sigma$ significance. This gives a solar $^8$B neutrino flux of ($8.4\pm3.1$)$\times$10$^6$ cm$^{-2}$s$^{-1}$, consistent with the standard solar model prediction. It is also the first indication of solar $^8$B neutrino ``fog'' in a dark matter direct detection experiment.