Test of Lepton Universality UsingB+→K+ℓ+ℓ−Decays

Abstract

A measurement of the ratio of the branching fractions of the B(+) → K(+)μ(+)μ(-) and B(+) → K(+)e(+)e(-) decays is presented using proton-proton collision data, corresponding to an integrated luminosity of 3.0 fb(-1), recorded with the LHCb experiment at center-of-mass energies of 7 and 8 TeV. The value of the ratio of branching fractions for the dilepton invariant mass squared range 1 < q(2) < 6 GeV(2)/c(4) is measured to be 0.745(-0.074)(+0.090)(stat) ± 0.036(syst). This value is the most precise measurement of the ratio of branching fractions to date and is compatible with the standard model prediction within 2.6 standard deviations.

Λb→(Λc, p)Dutta1 2016Phys. Rev. D593390View full textAdd to dashboardCite

“…Recently, LHCb collaboration [1] has measured the ratio of branching fractions of B → K e + e − to B → K µ + µ − decays to be R …”

Anomaly-free models for flavour anomalies

“…The LHCb Collaboration and other experiments have reported a number of anomalies in semileptonic B decays, including apparent violations of μ-e universality in B → K ( * ) + − decays [1][2][3][4], and apparent deviations from the Standard Model (SM) predictions for the P 5 angular variable in B → K * + − decay [5][6][7][8][9] and the m μ + μ − distribution in B s → φμ + μ − decay [10,11]. These anomalies have reached a high level of statistical significance.…”

A new generation of Lepton Flavour Universality observables from $B\rightarrow$$K^∗$$\mu^+$$\mu^−$

“…In 2015, the LHCb analysis [1] of the 3 fb −1 data on B → K * µ + µ − confirmed a ∼ 3σ anomaly in two large K * -recoil bins of the angular observable P 5 [2,3] that was already present in the 2013 results with 1 fb −1 [4]. The same experiment measured the observable R K = B(B → Kµ + µ − )/B(B → Ke + e − ) [5] in the dilepton mass range from 1 to 6 GeV 2 and found a 2.6σ tension with its SM value, predicted to be equal one (to a one per cent accuracy). Further deviations were observed by LHCb in two of the large-recoil bins of the branching ratio of B s → φ µ + µ − [6] but also in the lowrecoil bins of B + → K * + µ µ and B s → φ µ µ with a 2.5σ and 2.2σ deviation respectively.…”