Tree-level new physics in $R(K^{(*)})$

TL;DR

This paper develops a model-independent framework to analyze potential tree-level new physics effects in $R(K^{(*)})$, constraining new physics scales and couplings using a $ ext{chi}^2$ fit and existing experimental data.

Contribution

It introduces a systematic, model-independent parametrization of new physics in $R(K^{(*)})$, incorporating constraints from various processes and applying it to different new physics models.

Findings

New physics scale constrained to be below ~5 TeV.

Framework accommodates models like leptoquarks and $Z'$ bosons.

Comments on recent LHCb data aligning with Standard Model predictions.

Abstract

We implement the $\chi^2$ fit for $R(K^{(*)})$ with possible tree-level new physics in a model-independent parametrization. Relevant Wilson coefficients are decomposed into the new physics scale, its power, and the fermionic couplings. Constraints from the branching ratio of $B_s\to\mu^+\mu^-$ can be naturally incorporated with the scheme. For a reasonable set of the parameter ranges it is found that the new physics is less than $\sim 5~{\rm TeV}$. Some new physics models including the leptoquark, $Z'$, etc. can be embraced within our framework. We give comments on new LHCb data which are close to the standard model predictions.