Divalent lanthanoid ions in crystals for neutrino mass spectroscopy

TL;DR

This paper explores using divalent lanthanoid ions, especially Sm$^{2+}$ in crystals, as targets for neutrino mass spectroscopy via Raman photon scattering, aiming to determine neutrino properties.

Contribution

It identifies promising ion targets, calculates neutrino pair emission rates, and proposes methods to extract neutrino properties from Raman photon distributions.

Findings

Sm$^{2+}$ ions have high potential due to their optical properties and density.

Raman scattering can be used to distinguish neutrino mass types.

Background noise can be controlled by choosing specific Raman trigger directions.

Abstract

Electron spin flip in atoms or ions can cause neutrino pair emission, which provides a method to explore still unknown important neutrino properties by measuring spectrum of emitted photon in association, when electroweak rates are amplified by a phase coherence among participating atoms. Two important remaining neutrino issues to be determined are the absolute neutrino mass (or the smallest neutrino mass in the three-flavor scheme) and the nature of neutrino masses, either of Dirac type or of Majorana type. Use of Raman scattered photon was recently proposed as a promising tool for this purpose. In the present work we continue along this line to further identify promising ion targets in crystals, calculate neutrino pair emission rates, and study how to extract neutrino properties from Raman scattered photon angular distribution. Divalent lanthanoid ions in crystals, in particular Sm$^{2+}$, are the most promising, due to (1) its large number density, (2) sharp optical lines, (3) a variety of available ionic levels. Rejection of amplified quantum electrodynamic backgrounds is made possible to controllable levels by choosing a range of Raman trigger direction, when Sm$^{2+}$ sites are at O$_h$ inversion center of host crystals such as SrF$_2$.