Angular distributions in the decay B→K∗l+l−

Abstract

We use a sample of 384 × 10 6 B ¯¯¯ B 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 μ + μ − . For low dilepton invariant masses, m ℓ ℓ < 2.5 GeV / c 2 , we measure a lepton forward-backward asymmetry A FB = 0.24 + 0.18 − 0.23 ± 0.05 and K ∗ longitudinal polarization F L = 0.35 ± 0.16 ± 0.04 . For m ℓ ℓ > 3.2 GeV / c 2 , we measure A FB = 0.76 + 0.52 − 0.32 ± 0.07 and F L = 0.71 + 0.20 − 0.22 ± 0.04 .