Two old ways to measure the electron-neutrino mass

TL;DR

This paper reviews two traditional methods for measuring the electron-neutrino mass—single electron capture and neutrino-less double electron capture—highlighting recent technological advances and clarifying quantum physics misunderstandings.

Contribution

It provides a comprehensive review of old and new techniques for neutrino mass measurement, emphasizing recent progress and addressing misconceptions in the field.

Findings

Calorimetric EC can meet increased experimental challenges

Recent micro-calorimeter advancements improve measurement sensitivity

Clarification of quantum physics principles in EC experiments

Abstract

Three decades ago, the measurement of the electron neutrino mass in atomic electron capture (EC) experiments was scrutinized in its two variants: single EC and neutrino-less double EC. For certain isotopes an atomic resonance enormously enhances the expected decay rates. The favoured technique, based on calorimeters as opposed to spectrometers, has the advantage of greatly simplifying the theoretical analysis of the data. After an initial surge of measurements, the EC approach did not seem to be competitive. But very recently, there has been great progress on micro-calorimeters and the measurement of atomic mass differences. Meanwhile, the beta-decay neutrino-mass limits have improved by a factor of 15, and the difficulty of the experiments by the cube of that figure. Can the "calorimetric" EC theory cope with this increased challenge? I answer this question affirmatively. In so doing I briefly review the subject and extensively address some persistent misunderstandings of the underlying quantum physics.