Differential branching fractions and isospin asymmetries of B → K (*) μ + μ − decays

Abstract

The isospin asymmetries of B → Kµ + µ − and B → K * µ + µ − decays and the partial branching fractions of the B 0 → K 0 µ + µ − , B + → K + µ + µ − and B + → K * + µ + µ − decays are measured as functions of the dimuon mass squared, q 2 . The data used correspond to an integrated luminosity of 3 fb −1 from proton-proton collisions collected with the LHCb detector at centre-of-mass energies of 7 TeV and 8 TeV in 2011 and 2012, respectively. The isospin asymmetries are both consistent with the Standard Model expectations. The three measured branching fractions favour lower values than their respective theoretical predictions, however they are all individually consistent with the Standard Model.

Status of the $$B\rightarrow K^*\mu ^+\mu ^-$$ B → K ∗ μ +

“…• Angular observables in B 0 → K * 0 μ + μ − measured by CDF [45], LHCb [31], ATLAS* [37], and CMS* [38,46,47], • B 0,± → K * 0,± μ + μ − branching ratios by LHCb* [15,48], CMS [46,47], and CDF [45], Items marked with an asterisk have been updated since our previous global fit [32]. Concerning B 0 → K * 0 μ + μ − , both LHCb and ATLAS have performed measurements of CPaveraged angular observables S i as well as of the closely related "optimized" observables P i .…”

“…Further measurements have shown additional tensions, e.g. branching ratio measurements in B → K μ + μ − and B s → φμ + μ − [15,16], as well as, most notably, a hint for lepton flavour nonuniversality in B + → K + + − decays [17]. While progress has also been made on the theory side, most notably improved B → K * form factors from lattice QCD (LQCD) [18,19] and light-cone sum rules (LCSR) [20], the "anomaly" has also led to a renewed scrutiny of theoretical uncertainties due to form factors [21][22][23] as well as non-factorizable hadronic effects [24][25][26] (cf.…”

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.…”

Lepton Flavor Violation inBDecays?

“…LHCb also measured the B → Kµ + µ − branching ratio in this q 2 -range [7]. The updated result, based on its full Run I dataset of 3 fb −1 , is [8] B(B + → K + µ + µ − ) [1,6] = (1.19 ± 0.03 ± 0.06) × 10 −7 .…”

“…where we used B(B + → K + µ + µ − ) = (4.29 ± 0.22) × 10 −7 for the branching ratio integrated over q 2 [8]. The current limit, B(B + → K + µ ± e ∓ ) < 9.1 × 10 −8 [32], gives the weak bound…”