Correlating Non-Resonant Di-Electron Searches at the LHC to the Cabibbo-Angle Anomaly and Lepton Flavour Universality Violation

TL;DR

This paper links the Cabibbo angle anomaly and lepton flavour universality violation observed at the LHC through a common operator, providing a model-independent explanation consistent with existing bounds and predicting testable effects in upcoming experiments.

Contribution

It demonstrates a unified, model-independent explanation for LFUV signals at the LHC and the Cabibbo angle anomaly using a specific operator, without conflicting with current experimental bounds.

Findings

Correlates the Cabibbo angle anomaly with LHC LFUV signals.

Predicts a small deviation in pion decay ratios testable soon.

Finds a combined 4.5 sigma preference for the new physics hypothesis.

Abstract

In addition to the existing strong indications for lepton flavour university violation (LFUV) in low energy precision experiments, CMS recently released an analysis of non-resonant di-lepton pairs which could constitute the first sign of LFUV in high-energy LHC searches. In this article we show that the Cabibbo angle anomaly, an (apparent) violation of first row and column CKM unitarity with $\approx3\,\sigma$ significance, and the CMS result can be correlated and commonly explained in a model independent way by the operator $[Q_{\ell q}^{(3)}]_{1111} = (\bar{\ell}_1\gamma^{\mu}\sigma^I\ell_1)(\bar{q}_1\gamma_{\mu}\sigma^Iq_1)$. This is possible without violating the bounds from the non-resonant di-lepton search of ATLAS (which interestingly also observed slightly more events than expected in the electron channel) nor from $R(\pi)=\pi \to\mu\nu/\pi \to e \nu$. We find a combined preference for the new physics hypothesis of $4.5\,\sigma$ and predict $1.0004<R(\pi)<1.0009$ (95\%~CL) which can be tested in the near future with the forthcoming results of the PEN experiment.