New evaluation of neutron lifetime from UCN storage experiments and beam experiments

TL;DR

This paper reevaluates neutron lifetime measurements from UCN storage and beam experiments, analyzing discrepancies, systematic errors, and proposing improvements for future precision in measurements.

Contribution

It provides a new combined world average neutron lifetime and analyzes differences between UCN and beam experiment results, highlighting the need for improved beam experiment precision.

Findings

New world average neutron lifetime: 880.0 ± 0.9 s

UCN experiments average: 879.3 ± 0.6 s

Beam experiments average: 889.1 ± 2.9 s

Abstract

The analysis of experiments on measuring neutron lifetime has been made. The latest most accurate result of measuring neutron lifetime [Phys. Lett. B 605, 72 (2005)] 878.5 \pm 0.8 s differs from the world average value [Phys. Lett. B 667, 1 (2008)] 885.7 \pm 0.8 s by 6.5 standard deviations. In view of this both the analysis and the Monte Carlo simulation of experiments [Phys. Lett. B 483, 15 (2000)] and [Phys. Rev. Lett. 63, 593 (1989)] have been performed. Systematic errors about -6 s have been found in both experiments. The table of results of neutron lifetime measurements is given after corrections and additions have been made. A new world average value of neutron lifetime makes up 880.0 \pm 0.9 s. Here is also presented a separate analysis of experiments on measuring neutron lifetime with UCN and experiments on the beams. The average neutron lifetime for experiments with UCN is equal to 879.3(0.6) s, while for experiments on the beams it is equal to 889.1(2.9) s. The present difference of average values for both groups is (3.3 sigma) and needs consideration. The contribution of beam experiments into the world average value is not high, therefore it does not influence the above analysis. However, it is an independent problem to be solved. It seems desirable that the precision of beam experiments should be enhanced.