Solar neutrino detection in liquid xenon detectors via charged-current scattering to excited states

Abstract

We investigate the prospects for real-time detection of solar neutrinos via the charged-current neutrino-nucleus scattering process in liquid xenon time projection chambers. We use a nuclear shell model, benchmarked with experimental data, to calculate the cross sections for populating specific excited states of the caesium nuclei produced by neutrino capture on 131 Xe and 136 Xe. The shell model is further used to compute the decay schemes of the low-lying 1 + excited states of 136 Cs, for which there is sparse experimental data. We explore the possibility of tagging the characteristic de-excitation γ-rays/conversion electrons using two techniques: spatial separation of their energy deposits using event topology and their time separation using delayed coincidence. The efficiencies in each case are evaluated within a range of realistic detector parameters. We find that the topological signatures are likely to be dominated by radon backgrounds, but that a delayed coincidence signature from long-lived states predicted in 136 Cs may enable background-free detection of CNO neutrino interactions in next-generation experiments with smaller uncertainty than current measurements. We also estimate the sensitivity as a function of exposure for detecting the solar-temperature-induced line shift in 7 Be neutrino emission, which may provide a new test of solar models.