Stimulated X-rays in resonant atom Majorana mixing

TL;DR

This paper explores the resonant mixing of atoms via neutrinoless double electron capture as a method to detect Majorana neutrinos, proposing stimulated X-ray emission as a novel observable with potential high gain.

Contribution

It introduces a new approach to detect Majorana neutrinos through resonant atom mixing and stimulated X-ray emission, differing from traditional neutrinoless double beta decay methods.

Findings

Resonant enhancement occurs at near-degenerate atomic states.

Stimulated X-ray emission can be significantly amplified, with a gain factor of 100.

The method offers a background-free signature for Majorana neutrino detection.

Abstract

Massive neutrinos demand to ask whether they are Dirac or Majorana particles. Majorana neutrinos are an irrefutable proof of physics beyond the Standard Model. Neutrinoless double electron capture is not a process but a virtual $\Delta L=2$ mixing between a parent $^AZ$ atom and a daughter $^A(Z-2)$ excited atom with two electron holes. As a mixing between two neutral atoms and the observable signal in terms of emitted two-hole X-rays, the strategy, experimental signature and background are different from neutrinoless double beta decay. The mixing is resonantly enhanced for almost degeneracy and, under these conditions, there is no irreducible background from the standard two-neutrino channel. We reconstruct the natural time history of a nominally stable parent atom since its production either by nature or in the laboratory. After the time periods of atom oscillations and the decay of the short-lived daughter atom, at observable times the relevant "stationary" states are the mixed metastable long-lived state and the short-lived excited state, as well as the ground state of the daughter atom. Their natural population inversion is most appropriate for exploiting the bosonic nature of the observed X-rays by means of stimulating X-ray beams. Among different observables of the atom Majorana mixing, we include the enhanced rate of stimulated X-ray emission from the long-lived metastable state by a high-intensity X-ray beam. A gain factor of 100 can be envisaged in a facility like European XFEL.