Progress on the BL2 beam measurement of the neutron lifetime.

Shannon Fogwell Hoogerheide ,Ripan Biswas,Sai Meghasena Chavali,Jimmy Caylor,David M Gilliam,Geoffrey L Greene,Fangchen Li,Daniel Valete,H P Mumm ,C Deangelis ,E Anderson ,W M Snow ,B E Crawford ,Juliet Ivanov ,N Fomin ,M S Dewey ,F E Wietfeldt ,J Mulholland ,Evan Adamek ,Robert Haun ,Kyle Grammer ,J S Nico ,Andrew Yue

doi:10.1051/epjconf/201921903002

Abstract

A precise value of the neutron lifetime is important in several areas of physics, including determinations of the quark-mixing matrix element │V ud│, related tests of the Standard Model, and predictions of light element abundances in Big Bang Nucleosynthesis models. We report the progress on a new measurement of the neutron lifetime utilizing the cold neutron beam technique. Several experimental improvements in both neutron and proton counting that have been developed over the last decade are presented. This new effort should yield a final uncertainty on the lifetime of 1 s with an improved understanding of the systematic effects.

Highlights

The process in which a neutron is transformed into a proton, electron, and electron antineutrino, is well described by the charged weak current model as a left-handed, purely V −A interaction
As the prototypical nuclear beta decay, it is sensitive to certain Standard Model extensions in the charged-current sector
While the most precise determination of the Cabibbo-KobayashiMaskawa (CKM) matrix element |Vud| is currently obtained from 0+ → 0+ nuclear decays, it can be determined via neutron decay through increasingly precise measurements of the neutron lifetime and either the beta asymmetry coefficient [1, 2] or the electron-antineutrino angular correlation coefficient [3, 4]

Summary

Introduction

The process in which a neutron is transformed into a proton, electron, and electron antineutrino, is well described by the charged weak current model as a left-handed, purely V −A interaction. While the most precise determination of the Cabibbo-KobayashiMaskawa (CKM) matrix element |Vud| is currently obtained from 0+ → 0+ nuclear decays, it can be determined via neutron decay through increasingly precise measurements of the neutron lifetime and either the beta asymmetry coefficient [1, 2] or the electron-antineutrino angular correlation coefficient [3, 4]. In this paper we give an overview of the effort currently underway at NIST to measure the neutron lifetime using a cold neutron beam. We conclude with the status and outlook of this experiment

The beam method

Neutron counting

Proton counting

Analysis

Progress and outlook