Measurement of the Proton Asymmetry Parameter C in Neutron Beta Decay

TL;DR

This paper reports the first measurement of the proton asymmetry parameter C in neutron beta decay, confirming Standard Model predictions and providing a new parameter for testing fundamental physics.

Contribution

It presents the first experimental determination of the proton asymmetry parameter C in neutron decay, along with a differential analysis to extract the coupling constant ratio lambda.

Findings

C = -0.2377(26), consistent with Standard Model

Derived lambda = -1.275(16) from data

Provides new data for Standard Model tests

Abstract

The proton asymmetry parameter C in neutron decay describes the correlation between neutron spin and proton momentum. In this Letter, the first measurement of this quantity is presented. The result C=-0.2377(26) agrees with the Standard Model expectation. The coefficient C provides an additional parameter for new and improved Standard Model tests. From a differential analysis of the same data (assuming the Standard Model), we obtain lambda=-1.275(16) as ratio of axial-vector and vector coupling constant.