SNuDD: Solar Neutrinos for Direct Detection

We introduce Solar Neutrinos for Direct Detection (SNuDD): an open-source Python package that enables the computation of the solar neutrino rate spectrum at direct detection experiments. SNuDD can be used to determine the differential rate for both nuclear and electron recoils within the Standard Model and in the presence of beyond Standard Model physics effects, such as those arising from neutral-current non-standard interactions (NSI). The package accounts for matter effects during neutrino propagation through both the Sun and the Earth and for modifications to the scattering cross sections at the interaction site. We employ SNuDD to place new limits on the effective NSI couplings using results from the xenon-based direct detection experiments LZ, XENONnT, and PandaX-4T, and we project the sensitivity of a future xenon detector based on the planned XLZD and PandaX-xT observatories. We find that current direct detection experiments are rapidly approaching sensitivities comparable to those of dedicated neutrino experiments and that future xenon detectors can provide leading constraints. We recommend that SNuDD be used to combine incoming direct detection data with those from neutrino experiments in future global fits, placing direct detection within the broader landscape of neutrino physics.