Macroscopic neutrinoless double beta decay: long range quantum coherence

TL;DR

This paper introduces the concept of macroscopic neutrinoless double beta decay (MDBD), a quantum coherence phenomenon involving neutrino exchange over macroscopic distances, with potential experimental implications.

Contribution

The paper redefines MDBD in light of modern neutrino understanding, highlighting its quantum coherence over macroscopic scales and evaluating its rate in practical materials.

Findings

MDBD involves a coherent sum over neutrino mass states.

The total electron kinetic energy equals twice the single beta decay endpoint.

Background from two separate beta decays can be effectively rejected.

Abstract

We re-introduce, in light of our modern understanding of neutrinos, the concept of ``macroscopic neutrinoless double beta decay" (MDBD) for Majorana neutrinos. In this process an antineutrino produced by a nucleus undergoing beta decay, $X\to Y + e^- + \bar \nu_e$, is absorbed as a neutrino by another identical $X$ nucleus via the inverse beta decay reaction, $\nu_e + X \to e^-+Y$. The distinct signature of MDBD is that the total kinetic energy of the two electrons equals twice the endpoint energy of single beta decay. The amplitude for MDBD, a coherent sum over the contribution of different mass states of the intermediate neutrinos, reflects quantum coherence over macroscopic distances, and is a new macroscopic quantum effect. We evaluate the rate of MDBD for a macroscopic sample of ``$X$" material, e.g., tritium, acting both as the source and the target. The accidental background for MDBD originating from two separate single beta decays, which contains two final state neutrinos, can be readily rejected by measuring the energy of the detected two electrons. We discuss the similarities and differences between the MDBD and conventional neutrinoless double beta decay.