Scattering of low energy neutrinos and antineutrinos by atomic electrons

TL;DR

This paper investigates how atomic electron binding affects low-energy neutrino and antineutrino scattering, providing detailed calculations for ionization spectra in various atoms and energies, crucial for neutrino detection experiments.

Contribution

It introduces a full collision dynamics approach using the Bound Interaction Picture to accurately model atomic electron ionization by low-energy neutrinos, improving upon previous free-electron approximations.

Findings

Binding effects increase with atomic number and are most significant at low neutrino energies.

For 5 keV neutrinos scattering on neon, ionization spectra are reduced to less than 10% of free-electron predictions.

Final electron state modeling significantly impacts the calculated energy spectra.

Abstract

Studies of neutrino mixing and oscillations, solar neutrinos as background in dark matter searches involving electron detection, detection of sterile neutrino warm dark matter, and of possible electromagnetic properties of neutrinos, have generated interest in the low energy O(10 keV) scattering of electron neutrinos and antineutrinos by atomic electrons where the binding of the atomic electron cannot be ignored. Of particular interest is the ionization of atoms by neutrinos and antineutrinos. Most existing calculations are based on modifications of the free electron differential cross section, which destroy the relationship between the neutrino helicities and the orbital and spin angular momenta of the atomic electrons. The present calculations maintain the full collision dynamics by formulating the scattering in configuration space using the Bound Interaction Picture, rather than the usual formulation in the Interaction Picture in momentum space as appropriate to scattering by free electrons. Energy spectra of ionization electrons produced by scattering of neutrinos and antineutrinos with energies of 5, 10, 20, and 30 keV by hydrogen, helium and neon have been calculated using Dirac central field eigenfunctions and are presented as ratios to the spectra for scattering by free electrons. Binding effects increase strongly with atomic number, are largest for low neutrino energy and, for each neutrino energy, greatest at the high electron energy end of the spectrum. The most extreme effects of binding are for 5 keV scattering by Ne where the ratios are less than 0.1. The energy spectra are calculated for both a Coulombic final electron state and a free final electron state. The results indicate that the binding effects from the continuum state of the final electron are significant and can be comparable to those arising from the bound initial electron state.