Evidence for K→ K*ℓ+ℓ– and measurement of B→ Kℓ+ℓ–

Abstract

We present evidence for the flavor-changing neutral current decay B→ K*l+l– and a measurement of the B→ Kl+l– branching fraction, where l+l– is either an e+e– or μ+μ– pair. The data sample analyzed comprises 88.5× 106 $\Upsilon(4S)\to B\bar B$ decays collected with the BABAR detector at the PEP-II e+e– storage ring. Averaging over K(*) isospin and lepton flavor, we obtain ${\cal B}(B\to K^*\ell^{+}\ell^{-})= (1.40^{+0.57}_{-0.49}\pm0.21)\times 10^{-6}$ and ${\cal B}(B\to K\ell^{+}\ell^{-})=(0.68^{+0.17}_{-0.15}\pm0.04)\times 10^{-6}$ , where the uncertainties are statistical and systematic. The significance for the B→ K*l+l– signal is 3.0σ and for B→ Kl+l– the signal significance is over 7σ. PACS: 13.25.Hw – 13.20.He