Directional recoil detection for CEvNS measurements with light nuclei at the Spallation Neutron Source

The coherent elastic scattering of neutrinos on nuclei, also known as CE ν NS , has been studied for several years by the COHERENT program of experiments using neutrinos from stopped-pion decays produced at the Oak Ridge Spallation Neutron Source (SNS). We propose a new approach for CE ν NS measurements at the SNS that aims to complement the COHERENT experiments in two main ways: by reconstructing the distribution of CE ν NS -induced recoils, and by measuring CE ν NS on much lighter target nuclei such as helium, carbon, and fluorine. The proposed detector would employ a gaseous time-projection chamber with a highly segmented charge readout to enable the spatial reconstruction of ∼ 10 – 500 keV ionization tracks created by CE ν NS -induced recoils. This would enable the simultaneous measurement of the CE ν NS recoil energy and scattering angle, thereby allowing event-by-event reconstruction of the neutrino energy. We estimate that a 60 ∶ 40 He: CF 4 gas mixture at atmospheric pressure offers a good trade-off between total target mass and good directionality and could deliver a detection of the angular distribution of CE ν NS , even under pessimistic background conditions. We project the sensitivity of 1 and 10 m 3 -scale detectors in the context of several physics cases, including: the measurement of the Standard Model CE ν NS cross section, reconstruction of the flavor-dependent neutrino fluxes, observing the neutrino-induced Migdal effect, constraints on beyond-Standard-Model neutrino interactions, and probing 10-eV-scale sterile neutrinos.