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(4S) 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)×10^{-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^{-})<3.1×10^{-6}.
Highlights
We report the observation of the rare charm decay D0 → K−πþeþe−, based on 468 fb−1 of eþe− annihilation data collected at or close to the center-of-mass energy of the Υð4SÞ resonance with the BABAR detector at the SLAC National Accelerator Laboratory
We find the branching fraction in the invariant mass range 0.675 < mðeþe−Þ < 0.875 GeV=c2 of the electron-positron pair to be BðD0 → K−πþeþe−Þ 1⁄4 ð4.0 Æ 0.5 Æ 0.2 Æ 0.1Þ × 10−6, where the first uncertainty is statistical, the second systematic, and the third due to the uncertainty in the branching fraction of the decay D0 → K−πþπþπ− 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 D0 → K−πþμþμ− branching fraction, measured in the same invariant mass range, and with the value expected in the standard model
Summary
Candidate D0 mesons are formed from four charged tracks reconstructed with the appropriate mass hypothesis for the D0 → K−πþeþe− and D0 → K−πþπþπ− decays. To reject misreconstructed D0 → K−πþeþe− candidates that originate from D0 hadronic decays with large branching fractions where one or more charged tracks are misidentified by the PID the candidate is reconstructed assuming the kaon or pion mass hypothesis for the leptons. After the application of all selection criteria and corrections for small differences between data and MC simulation in tracking and PID performance, the average reconstruction efficiency for the D0 → K−πþπþπ− decay is εnorm 1⁄4 ð20.1 Æ 0.2Þ%, where the uncertainty is due to the limited size of the simulation sample. The D0 → K−πþeþe− branching fraction is determined relative to that of the normalization decay channel D0 → K−πþπþπ− using
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