Test of lepton universality using B+ →k+l+l- decays

The ratio of branching fractions of the decays Λ 0 b → pK − e + e − and Λ 0 b → pK − µ + µ − , 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 ± 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 Λ 0 b → pK − e + e − .

Physical Review Letters, 2019

A measurement of the ratio of branching fractions of the decays B + → K + µ + µ − and B + → K + e + e − is presented. The proton-proton collision data used correspond to an integrated luminosity of 5.0 fb −1 recorded with the LHCb experiment at centre-of-mass energies of 7, 8 and 13 TeV. For the dilepton mass-squared range 1.1 < q 2 < 6.0 GeV 2 /c 4 the ratio of branching fractions is measured to be R K = 0.846 + 0.060 − 0.054 + 0.016 − 0.014 , where the first uncertainty is statistical and the second systematic. This is the most precise measurement of R K to date and is compatible with the Standard Model at the level of 2.5 standard deviations.

2021

Tests of lepton universality in B0→ K0 S`` and B+→ K∗+`+`− decays where ` is either an electron or a muon are presented. The differential branching fractions of B0→ K0 See and B+→ K∗+e+e− decays are measured in intervals of the dilepton invariant mass squared. The measurements are performed using proton-proton collision data recorded by the LHCb experiment, corresponding to an integrated luminosity of 9 fb−1. The results are consistent with the Standard Model and previous tests of lepton universality in related decay modes. The first observation of B0→ K0 See and B+→ K∗+e+e− decays is reported. Submitted to Phys. Rev. Lett. © 2021 CERN for the benefit of the LHCb collaboration. CC BY 4.0 licence. †Authors are listed at the end of this paper. ar X iv :2 11 0. 09 50 1v 1 [ he pex ] 1 8 O ct 2 02 1

Journal of High Energy Physics, 2020

The ratio of branching fractions of the decays Λ 0 b → pK − e + e − and Λ 0 b → pK − µ + µ − , 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 ± 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 Λ 0 b → pK − e + e − .

2018

Three tests of lepton flavour universality in semitauonic B decays using LHCb Run 1 data are presented. Namely, these are measurements of the ratios of branching fractions of B0-&gt;D* (tau/mu) nu (using both muonic and 3-prong hadronic tau decays) and Bc-&gt;J/psi (tau/mu) nu (using the muonic tau decay). All three results, along with similar measurements from BaBar and Belle, lie above the Standard Model prediction, hinting at the violation of lepton flavour universality. Prospects for future improvements in precision are also discussed.

2023

Physical Review Letters, 2004

We determine the inclusive B --> Xc l nu branching fraction, the CKM matrix element |Vcb|, and other heavy-quark parameters from a simultaneous fit to moments of the hadronic-mass and lepton-energy distributions in semileptonic B-meson decays, measured as a function of the lower limit on the lepton energy, using data recorded with the BABAR detector. Using Heavy Quark Expansions (HQEs) to order 1/mb^3, we extract BR_cenu=(10.61 +- 0.16(exp) +- 0.06(HQE))% and |Vcb| = (41.4 +- 0.4(exp) +- 0.4(HQE) +- 0.6(th)) 10^-3. The stated errors refer to the experimental, HQE, and additional theoretical uncertainties.

Physical review letters, 2018

The ratio of branching fractions R(D^{*-})≡B(B^{0}→D^{*-}τ^{+}ν_{τ})/B(B^{0}→D^{*-}μ^{+}ν_{μ}) is measured using a data sample of proton-proton collisions collected with the LHCb detector at center-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of 3 fb^{-1}. For the first time, R(D^{*-}) is determined using the τ-lepton decays with three charged pions in the final state. The B^{0}→D^{*-}τ^{+}ν_{τ} yield is normalized to that of the B^{0}→D^{*-}π^{+}π^{-}π^{+} mode, providing a measurement of B(B^{0}→D^{*-}τ^{+}ν_{τ})/B(B^{0}→D^{*-}π^{+}π^{-}π^{+})=1.97±0.13±0.18, where the first uncertainty is statistical and the second systematic. The value of B(B^{0}→D^{*-}τ^{+}ν_{τ})=(1.42±0.094±0.129±0.054)% is obtained, where the third uncertainty is due to the limited knowledge of the branching fraction of the normalization mode. Using the well-measured branching fraction of the B^{0}→D^{*-}μ^{+}ν_{μ} decay, a value of R(D^{*-})=0.291±0.019±0.026±0.013 is establish...

Physics Letters B, 1991

We have measured the decay properties of Z°-.bb from a study of inclusive muon and electron events. The average (e and it) b-quark semileptonic branching ratio has been determined to be BR (b--, £ + X ) = 0.119 + 0.003 (stat.) + 0.006 (syst.), assuming the standard model prediction of Fb6 = 378 + 3 MeV. From the ratio of the number of dilepton events to single lepton events, we find BR (b~ + X )= 0.113 + 0.010 (stat.) + 0,006 (syst.), without assumptions on Fb~. The partial decay width of the Z ° into bl~ has been measured to be Fb6 = 385 + 7(stat. )+ 11 (syst.) MeV with an additional 19 MeV error from the uncertainty in BR (b--*~ + X). The average fractional energy of bottom hadrons in Z°--.bl~ events has been determined to be (xe)= 0.686 + 0.006 (stat.) + 0.016(syst.).

Physical Review Letters, 2011

The relative abundance of the three decay modes B 0 ! D À K þ , B 0 ! D À þ , and B 0 s ! D À s þ produced in 7 TeV pp collisions at the LHC is determined from data corresponding to an integrated luminosity of 35 pb À1 . The branching fraction of B 0 ! D À K þ is found to be BðB 0 ! D À K þ Þ ¼ ð2:01 AE 0:18 stat AE 0:14 syst Þ Â 10 À4 . The ratio of fragmentation fractions f s =f d is determined through the relative abundance of B 0 s ! D À s þ to B 0 ! D À K þ and B 0 ! D À þ , leading to f s =f d ¼ 0:253 AE 0:017 AE 0:017 AE 0:020, where the uncertainties are statistical, systematic, and theoretical, respectively.