Limits on Tensor Coupling from Neutron $\beta$-Decay

TL;DR

This paper establishes limits on tensor couplings in neutron beta decay by analyzing experimental data and comparing it with standard model predictions, providing constraints on beyond standard model physics.

Contribution

It derives new bounds on tensor couplings from neutron decay measurements, combining various experimental parameters and theoretical inputs for improved constraints.

Findings

Most stringent limit: -0.0026 < C_T/C_A < 0.0024 (95% C.L.)

Limits are based on electron-neutrino and beta asymmetry measurements

Constraints assume no right-handed currents.

Abstract

Limits on the tensor couplings generating a Fierz interference term, b, in mixed Gamow-Teller Fermi decays can be derived by combining data from measurements of angular correlation parameters in neutron decay, the neutron lifetime, and $G_{\text{V}}=G_{\text{F}} V_{ud}$ as extracted from measurements of the $\mathcal{F}t$ values from the $0^{+} \to 0^{+}$ superallowed decays dataset. These limits are derived by comparing the neutron $\beta$-decay rate as predicted in the standard model with the measured decay rate while allowing for the existence of beyond the standard model couplings. We analyze limits derived from the electron-neutrino asymmetry, $a$, or the beta-asymmetry, $A$, finding that the most stringent limits for $C_\text{T}/C_\text{A}$ under the assumption of no right-handed currents is $-0.0026 < C_\text{T}/C_\text{A} < 0.0024$ (95% C.L.) for the two most recent values of $A$.