New Physics Constraints from Atomic Parity Violation in $^{133}$Cs

TL;DR

This paper presents an improved theoretical calculation of atomic parity violation in cesium, leading to a more precise measurement of the nuclear weak charge and implications for physics beyond the Standard Model.

Contribution

It introduces a novel relativistic coupled-cluster method that accurately accounts for core, valence, and excited state contributions in atomic parity violation calculations.

Findings

Measured $Q_W$ deviates from the Standard Model prediction.

New calculation reduces theoretical uncertainties.

Results suggest potential hints of new physics.

Abstract

Our improved calculation of the nuclear spin-independent parity violating electric dipole transition amplitude ($E1_{PV}$) for $6s ~ ^2S_{1/2} - 7s ~ ^2S_{1/2}$ in $^{133}$Cs in combination with the most accurate (0.3\%) measurement of this quantity yields a new value for the nuclear weak charge $Q_W=-73.71(26)_{ex} (23)_{th}$ against the Standard Model (SM) prediction $Q_W^{\text{SM}}=-73.23(1)$. The advances in our calculation of $E1_{PV}$ have been achieved by using a variant of the perturbed relativistic coupled-cluster theory which treats the contributions of the core, valence and excited states to $E1_{PV}$ on the same footing unlike the previous high precision calculations. Furthermore, this approach resolves the controversy regarding the sign of the core correlation effects. We discuss the implications of the deviation of our result for $Q_W$ from the SM value by considering different scenarios of new physics.