First Indication of Solar B8 Neutrinos via Coherent Elastic Neutrino-Nucleus Scattering with XENONnT

We present the first measurement of nuclear recoils from solar B8 neutrinos via coherent elastic neutrino-nucleus scattering with the XENONnT dark matter experiment. The central detector of XENONnT is a low-background, two-phase time projection chamber with a 5.9 t sensitive liquid xenon target. A blind analysis with an exposure of 3.51 t×yr resulted in 37 observed events above 0.5 keV, with (26.4-1.3+1.4) events expected from backgrounds. The background-only hypothesis is rejected with a statistical significance of 2.73σ. The measured B8 solar neutrino flux of (4.7-2.3+3.6)×106 cm-2 s-1 is consistent with results from the Sudbury Neutrino Observatory. The measured neutrino flux-weighted CEνNS cross section on Xe of (1.1-0.5+0.8)×10-39 cm2 is consistent with the Standard Model prediction. This is the first direct measurement of nuclear recoils from solar neutrinos with a dark matter detector.