Measurement of the B ⁰ → K ^*0 e ⁺ e ^- Branching fraction at low dilepton mass

The branching fraction of the rare decay B ⁰ → K ^*0 e ⁺ e ^- in the dilepton mass region from 30 to 1000 MeV/c ² has been measured by the LHCb experiment, using pp collision data, corresponding to an integrated luminosity of 1.0 fb^-1, at a centre-of-mass energy of 7 TeV. The decay mode B ⁰ → J/ψ (e ⁺ e ^-)K ^*0 is utilized as a normalization channel. The branching fraction B(B ⁰ → K ^*0 e ⁺ e ^-) is measured to be B(B ⁰ → K ^*0 e ⁺ e ^-)^{30-1000 MeV/c2}=(3.1^+0.9 _-0.8^0.2_-0.3 ± 0.2) × 10 ^-7 where the first error is statistical, the second is systematic, and the third comes from the uncertainties on the B ⁰ → J/ψ K ^*0 and J/ψ → e ⁺ e ^- branching fractions. [Figure not available: see fulltext.]