Bounds on new neutrino interactions from the first CE$ν$NS data at direct detection experiments

Abstract: Recently, two dark matter direct detection experiments have announced the first indications of nuclear recoils from solar $^8$B neutrinos via coherent elastic neutrino-nucleus scattering (CE$\nu$NS) with xenon nuclei. These results constitute a turning point, not only for dark matter searches that are now entering the \textit{neutrino fog}, but they also bring out new opportunities to exploit dark matter facilities as neutrino detectors. We investigate the implications of recent data from the PandaX-4T and XENONnT experiments on both Standard Model physics and new neutrino interactions. We first extract information on the weak mixing angle at low momentum transfer. Then, following a phenomenological approach, we consider Lorentz-invariant interactions (scalar, vector, axial-vector, and tensor) between neutrinos, quarks and charged leptons. Furthermore, we study the $U(1)_\mathrm{B-L}$ scenario as a concrete example of a new anomaly-free vector interaction. We find that despite the low statistics of these first experimental results, the inferred bounds are in some cases already competitive. For the scope of this work we also compute new bounds on some of the interactions using CE$\nu$NS data from COHERENT and electron recoil data from XENONnT, LUX-ZEPLIN, PandaX-4T, and TEXONO. It seems clear that while direct detection experiments continue to take data, more precise measurements will be available, thus allowing to test new neutrino interactions at the same level or even improving over dedicated neutrino facilities.