New insights into nuclear physics and weak mixing angle using electroweak probes

TL;DR

This paper combines neutrino scattering and atomic parity violation data to precisely measure neutron radii and the weak mixing angle, providing new insights into nuclear structure and electroweak interactions.

Contribution

It introduces the first combined analysis of COHERENT and APV data to measure neutron skin and weak mixing angle with high precision, independent of neutron radius assumptions.

Findings

Neutron rms radii of $^{133}$Cs and $^{127}$I are precisely measured.

The weak mixing angle is determined with percent uncertainty, slightly above the Standard Model prediction.

Results favor models with larger neutron skin values, consistent with PREX measurements.

Abstract

Using the new results on coherent elastic neutrino-nucleus scattering data in cesium-iodide provided by the COHERENT experiment, we determine a new measurement of the average neutron rms radius of $^{133}\text{Cs}$ and $^{127}\text{I}$. In combination with the atomic parity violation (APV) experimental result, we derive the most precise measurement of the neutron rms radii of $^{133}\text{Cs}$ and $^{127}\text{I}$, disentangling for the first time the contributions of the two nuclei. By exploiting these measurements we determine the corresponding neutron skin values for $^{133}\text{Cs}$ and $^{127}\text{I}$. These results suggest a preference for models which predict large neutron skin values, as corroborated by the only other electroweak measurements of the neutron skin of $^{208}\text{Pb}$ performed by PREX experiments. Moreover, for the first time, we obtain a data-driven APV+COHERENT measurement of the low-energy weak mixing angle with a percent uncertainty, independent of the value of the average neutron rms radius of $^{133}\text{Cs}$ and $^{127}\text{I}$, that is allowed to vary freely in the fit. The value of the low-energy weak mixing angle that we found is slightly larger than the standard model prediction.