Correlating nonresonant di-electron searches at the LHC to the Cabibbo-angle anomaly and lepton flavor universality violation

Abstract

In addition to the existing strong indications for lepton flavor universality violation in low-energy precision experiments, the CMS Collaboration at CERN recently released an analysis of nonresonant dilepton pairs which could constitute the first sign of lepton flavor universality violation in high-energy searches at the LHC. In this article, we show that the Cabibbo-angle anomaly, an (apparent) violation of first row and column Cabibbo-Kobayashi-Maskawa (CKM) matrix unitarity with $\ensuremath{\approx}3\ensuremath{\sigma}$ significance, and the CMS result can be correlated and commonly explained in a model-independent way by the operator $[{Q}_{\ensuremath{\ell}q}^{(3)}{]}_{1111}=({\overline{\ensuremath{\ell}}}_{1}{\ensuremath{\gamma}}^{\ensuremath{\mu}}{\ensuremath{\sigma}}^{I}{\ensuremath{\ell}}_{1})({\overline{q}}_{1}{\ensuremath{\gamma}}_{\ensuremath{\mu}}{\ensuremath{\sigma}}^{I}{q}_{1})$. This is possible without violating the bounds from the nonresonant dilepton search of ATLAS (which interestingly also observed slightly more events than expected in the electron channel) nor from $R(\ensuremath{\pi})=\ensuremath{\pi}\ensuremath{\rightarrow}\ensuremath{\mu}\ensuremath{\nu}/\ensuremath{\pi}\ensuremath{\rightarrow}e\ensuremath{\nu}$. We find a combined preference for the new physics hypothesis of $4.5\ensuremath{\sigma}$ and predict $1.0004<R(\ensuremath{\pi})<1.0009$ (95% C.L.) which can be tested in the near future with the forthcoming results of the PEN experiment.