Comparison of two experiments on radiative neutron decay

TL;DR

This paper compares two experiments on radiative neutron decay, highlighting differences in methodology and results, and discusses the impact of magnetic fields on measurement accuracy.

Contribution

It provides a detailed comparison of two experimental approaches to radiative neutron decay, emphasizing the effects of magnetic fields on measurement validity.

Findings

The 2005 experiment discovered radiative neutron decay with a branching ratio of (3.2±1.6)×10⁻³.

The NIST experiment reported a similar branching ratio of (3.13±0.34)×10⁻³ but used magnetic fields that hinder accurate measurement.

Magnetic fields in the NIST experiment complicate the identification of decay events and the measurement of the branching ratio.

Abstract

Over 10 years ago we proposed an experiment on measuring the characteristics of radiative neutron decay in papers [1, 2]. At the same time we had published the theoretical spectrum of radiative gamma quanta, calculated within the framework of the electroweak interactions, on the basis of which we proposed the methodology for the future experiment [3,4]. However, because we were denied beam time on the intensive cold neutron beam at ILL (Grenoble, France) for a number of years, we could only conduct the experiment in 2005 on the newly opened FRMII reactor of Technical University of Muenchen. The main result of this experiment was the discovery of radiative neutron decay and the measurement of its relative intensity B.R.= (3.2+-1.6)10-3 with C.L.=99.7% for radiative gamma quanta with energy over 35 kev [5,6]. Over a year after our first announcement about the results of the conducted experiment, "Nature" [7] published a letter asserting that its authors have also measured the branching ratio of radiative neutron decay B.R.= (3.13+-0.34)10-3 with C.L.=68% and gamma quanta energy from 15 to 340 kev. This article aims to compare these two experiments. It is shown that the use of strong magnetic fields in the NIST (Washington, USA) experiment methodology not only prevents any exact measurement of the branching ratio and identification of radiative neutron decay events, but also makes registration of ordinary neutron decay events impossible.