Measurement of the Differential Branching Fraction and Forward-Backword Asymmetry for B->K(*)l+l-

TL;DR

This study measures various decay properties of B->K(*)l+l- processes using a large data sample, finding deviations in the forward-backward asymmetry from Standard Model predictions.

Contribution

It provides the first detailed measurement of differential branching fractions, isospin asymmetry, polarization, and AFB for B->K(*)l+l- decays with high precision.

Findings

AFB spectrum exceeds Standard Model expectations by 2.7 sigma.

Measured branching fractions are approximately 10.7 and 4.8 x 10^-7 for B->K* l+l- and B->K l+l-, respectively.

Muon to electron ratios are consistent with lepton universality within uncertainties.

Abstract

We study B->K(*)l+l- decays (l=e,mu) based on a data sample of 657 million 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 (AFB) as functions of q^2 = M_{ll}^2*c^2. The fitted AFB spectrum exceeds the Standard Model expectation by 2.7 standard deviations. The measured branching fractions are B(B->K*l+l-)=(10.7+1.1-1.0+-0.9)*10^-7 and B(B->Kl+l-)=(4.8+0.5-0.4+-0.3)*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+-0.05 and R_K=1.03+-0.19+-0.06, respectively.