Title: A Broader View of Neutron Beta Decay from the Nab Experiment at ORNL
Abstract: The weak force of nature uniquely allows quarks to change flavor, resulting in the transformation of nuclei known as nuclear beta decay. Currently, measurements of the weak mixing of quarks are in tension with the Standard Model's description, a discrepancy referred to as the "Cabibbo Angle Anomaly." As the simplest nucleus to undergo beta decay, the neutron has emerged as a system which can provide a competitive measurement and shine light on this anomaly if experimental uncertainties in the neutron dataset can be improved. The Nab experiment at the Spallation Neutron Source employs a novel and robust approach to improve decay correlation measurements by observing the full momentum phase space in neutron beta decay accessible above detection thresholds. The tight kinematic constraints from the experiment have recently been used to place first limits on a new hypothesized excited state of the neutron, suggested to address experimental disagreements in neutron lifetime measurements. In this presentation, I will describe the working principles of the experiment, present early results from first physics data-taking, and discuss the outlook for Nab and its upgrade pNAB (polarized Nab) to perform world-leading measurements of neutron decay correlations and improve our understanding of quark mixing in the weak interaction.