Test of lepton universality with $\Lambda^{0}_{b} \to p K^- \ell^+ \ell^-$ decays

TL;DR

This paper reports the first measurement of lepton universality in b baryon decays, specifically comparing electron and muon channels of $ ext{Lambda}_b^0$ decays, using LHCb data across multiple energies.

Contribution

It provides the first test of lepton universality with b baryons and reports the first observation of the decay $ ext{Lambda}_b^0 o pK^- e^+ e^-$.

Findings

Measured the ratio of branching fractions $R^{-1}_{pK} = 1.17^{+0.18}_{-0.16} ext{(stat)} ext{±} 0.07 ext{(syst)}$.

First observation of the decay $ ext{Lambda}_b^0 o pK^- e^+ e^-$.

Performed the first test of lepton universality with b baryons.

Abstract

The ratio of branching fractions of the decays $\Lambda^{0}_{b}\to pK^{-}e^{+}e^{-}$ and $\Lambda^{0}_{b}\to pK^{-}\mu^{+}\mu^{-}$, $R^{-1}_{pK}$, is measured for the first time using proton-proton collision data corresponding to an integrated luminosity of 4.7 $fb^{-1}$ recorded with the LHCb experiment at center-of-mass energies of 7, 8 and 13 TeV. In the dilepton mass-squared range $0.1 < q^{2} < 6.0$ $GeV^{2}/c^{4}$ and the $pK^{-}$ mass range $m(pK^{-}) < 2600$ $MeV/c^{2}$, the ratio of branching fractions is measured to be $R^{-1}_{pK} = 1.17 ^{+0.18}_{-0.16} \pm 0.07$, where the first uncertainty is statistical and the second systematic. This is the first test of lepton universality with b baryons and the first observation of the decay $\Lambda^{0}_{b}\to pK^{-}e^{+}e^{-}$.