Measurement of the Differential Branching Fraction and Forward-Backward Asymmetry forB→K(*)l+l−

Abstract

We study B --> K(*)l+l- decays (l = e, mu) based on a data sample of 657 x 10(6) BB pairs collected with the Belle detector at the KEKB e+e- collider. We report the differential branching fraction, isospin asymmetry, K* polarization, and the forward-backward asymmetry (A(FB)) as functions of q2 = M(ll)(2)c2. The fitted A(FB) spectrum exceeds the standard model expectation by 2.7 standard deviations. The measured branching fractions are B(B --> K*l+l-) = (10.7(-1.0)(+1.1) +/- 0.9) x 10(-7) and B(B --> Kl+l-) = (4.8(-0.4)(+0.5) +/- 0.3) x 10(-7), where the first errors are statistical and the second are systematic, with the muon to electron ratios R(K*) = 0.83 +/- 0.17 +/- 0.08 and R(K) = 1.03 +/- 0.19 +/- 0.06.

Differential branching fraction and angular analysis of the B + → K + μ + μ − decay

“…The differential branching fraction of the B + → K + µ + µ − decay is, however, consistently below the SM prediction at low q 2 . The results are in good agreement with, but statistically more precise than, previous measurements of dB/dq 2 and A FB from BaBar [39,40], Belle [41] and CDF [42]. Integrating the differential branching fraction, over the full q 2 range, yields a total branching fraction of (4.36 ± 0.15 ± 0.18) × 10 −7 , which is more precise than the current world average of (4.8 ± 0.4) × 10 −7 [30].…”

Diagnosing lepton-nonuniversality in b → sℓℓ

“…1 Previous measurements [3,4] had significantly larger uncertainties and were consistent with the SM prediction, which is R K = 1 to an excellent approximation [5]. Theory interpretations of the recent R K data are given in [6][7][8][9][10][11][12][13].…”

“…For simplicity, and to make the complementarity of the different decays manifest, the following expressions only include the dominant linear BSM contributions from interference with the SM. 3 Given the current experimental uncertainty of about 10% (1.2) these formulas are sufficiently precise. Nonetheless, for our numerical analyses and plots we use the full expressions including the quadratic BSM dependence.…”

Direct determination of Wilson coefficients using B0 → K∗0μ+μ− decays

“…[78]. Neglecting lepton mass effects the CP -averaged S i reduce to the longitudinal polarisation fraction F L = S 1c , the forward-backward asymmetry A FB = 3 4 S 6s and the remaining S 3,4,5,7,8,9 . Additional ratios of S i have been proposed as observables, for which form factor uncertainties cancel at leading order [79,80].…”

“…The angular distributions of the decay have been studied by the BaBar, Belle, CDF, CMS and LHCb collaborations [1][2][3][4][5][6][7][8][9][10]. The LHCb collaboration has performed the first full angular analysis using the full data sample from Run 1 of the LHC, corresponding to an integrated luminosity of 3 fb −1 [7].…”