Improved limits on Fierz interference using asymmetry measurements from the Ultracold Neutron Asymmetry (UCNA) experiment

Abstract

The UCNA Collaboration reanalyzed and combined results from previous experiments that measured the $\ensuremath{\beta}$-decay asymmetry for polarized ultracold neutrons confined in a trap in order to search for the so-called Fierz interference term. They demonstrate that systematic uncertainties from the asymmetry analysis related to the experimental efficiency and calibration can be reduced. This work suggests that a robust path forward to improved limits on the Fierz term in next-generation neutron-decay experiments exists and holds promise of providing an improved probe of whether physics beyond the Standard Model is at play.