Angular Distributions in the Decays B -> K* l+l-

TL;DR

This study analyzes angular distributions in B -> K* l+l- decays using a large dataset, measuring asymmetries and polarization to test the Standard Model and search for new physics effects.

Contribution

First measurement of angular distributions in B -> K* l+l- decays across different dilepton mass regions with high statistical precision.

Findings

Measured forward-backward asymmetry AFB in low and high mass regions.

Determined K* longitudinal polarization FL in both mass regions.

Results are consistent with Standard Model predictions within uncertainties.

Abstract

We use a sample of 384 million BBbar events collected with the Babar detector at the PEP-II e+e- collider to study angular distributions in the rare decays B -> K* l+l-, where l+l- is either e+e- or mu+mu-. For low dilepton invariant masses, m(l+l-)<2.5 GeV/c^2, we measure a lepton forward-backward asymmetry AFB=0.24 (+0.18,-0.23) +/- 0.05 and K* longitudinal polarization FL=0.35 +/- 0.16 +/- 0.04$. For m(l+l-)>3.2$ GeV/c^2, we measure AFB=0.76 (+0.52,-0.32) +/- 0.07 FL=0.71 (+0.20,-0.22) +/- 0.04.