Test of lepton flavour universality with $B^+ \to K^+\pi^+\pi^-\ell^+\ell^-$ decays

TL;DR

This paper reports the first test of lepton flavor universality in B+ decays to K+ pi+ pi- l+ l- using LHCb data, finding results consistent with the Standard Model and observing the electron mode for the first time.

Contribution

It presents the first measurement of lepton flavor universality in this decay channel and reports the first observation of the B+ to K+ pi+ pi- e+ e- decay.

Findings

Measured the ratio of branching fractions as 1.31^{+0.18}_{-0.17} (stat)^{+0.12}_{-0.09} (syst).

Results are consistent with Standard Model predictions.

First observation of B+ to K+ pi+ pi- e+ e- decay.

Abstract

The first test of lepton flavor universality between muons and electrons using $B^+ \to K^+\pi^+\pi^-\ell^+\ell^-$ ($\ell=e,\mu$) decays is presented. The measurement is performed with data from proton-proton collisions collected by the LHCb experiment at center-of-mass energies of 7, 8, and 13 TeV, corresponding to an integrated luminosity of $9\mathrm{fb}^{-1}$. The ratio of branching fractions between $B^+ \to K^+\pi^+\pi^-e^+e^-$ and $B^+ \to K^+\pi^+\pi^-\mu^+\mu^-$decays is measured in the dilepton invariant-mass-squared range $1.1 < q^2 < 7.0~\mathrm{GeV}^2/c^4$ and is found to be $R_{K\pi\pi}^{-1} = 1.31^{+0.18}_{-0.17} \;(\mathrm{stat})\;^{+0.12}_{-0.09} \;(\mathrm{syst})$, in agreement with the standard model prediction. The first observation of the $B^+ \to K^+\pi^+\pi^-e^+e^-$ decay is also reported.