Observation of the Decay D-0 -> K- pi(+) e(+) e(-)

Abstract

We report the observation of the rare charm decay D 0 → K − π + e + e − , based on 468

fb − 1 of e + e − annihilation data collected at or close to the center-of-mass energy of the Υ ( 4 S ) resonance with the BABAR detector at the SLAC National Accelerator Laboratory. We find the branching fraction in the invariant mass range 0.675 < m ( e + e − ) < 0.875

GeV / c 2 of the electron-positron pair to be B ( D 0 → K − π + e + e − ) = ( 4.0 ± 0.5 ± 0.2 ± 0.1 ) × 1 0 − 6 , where the first uncertainty is statistical, the second systematic, and the third due to the uncertainty in the branching fraction of the decay D 0 → K − π + π + π − used as a normalization mode. The significance of the observation corresponds to 9.7 standard deviations including systematic uncertainties. This result is consistent with the recently reported D 0 → K − π + μ + μ − branching fraction, measured in the same invariant mass range, and with the value expected in the standard model. In a set of regions of m ( e + e − ) , where long-distance effects are potentially small, we determine a 90% confidence level upper limit on the branching fraction B ( D 0 → K − π + e + e − ) < 3.1 × 1 0 − 6 .