Test of lepton flavour universality with $B^0\to K^{*0}\ell^+\ell^-$ decays at large dilepton invariant mass

TL;DR

This paper reports a precise test of lepton flavor universality in B meson decays, measuring the ratio of muon to electron decay rates at high dilepton mass, consistent with the Standard Model.

Contribution

First measurement of $R_{K^{*0}}$ at a hadron collider in the high dilepton mass region, providing the most precise test to date.

Findings

Measured $R_{K^{*0}}$ as 1.08 with uncertainties, consistent with Standard Model.

Used data from LHCb at 7, 8, and 13 TeV with 9 fb$^{-1}$ luminosity.

First such measurement at a hadron collider.

Abstract

Muon-electron universality is tested in $B^0 \to K^{*0} \ \ell^+ \ell^-$ decays, in the dilepton-invariant-mass region above the $\psi(2S)$ resonance. The analysis uses beauty mesons produced in proton-proton collisions recorded by the LHCb detector at center-of-mass energies of 7, 8, and 13 $\text{TeV}$, corresponding to an integrated luminosity of 9 $\text{fb}^{-1}$. The ratio of branching fractions between the muon and electron channels, $R_{K^{*0}}$, is measured to be $1.08\,^{+0.14}_{-0.12}\text{(stat)} \ \pm 0.07\text{(syst)}$ for a dilepton-invariant-mass squared above 14.0 $\text{GeV}^{2}/\text{c}^{4}$, consistent with the Standard Model prediction. This result represents the most precise measurement of $R_{K^{*0}}$ in this region and the first such measurement performed at a hadron collider.