Speaker
Description
Flavor-changing neutral current (FCNC) processes are rare within the Standard Model (SM) as they cannot occur at tree level and are suppressed at loop level by the Glashow-Iliopoulos-Maiani (GIM) mechanism. In $D$-meson decays, the GIM cancellation is almost exact, leading to expected branching fractions for $c\to u l^- l^+$ processes of order $\mathcal{O}(10^{-9})$. However, long-distance effects can raise this to $\mathcal{O}(10^{-6})$. In this talk, we report on the observation of the $D^0\to K^-\pi^+e^+e^-$ decay, based on a sample of about 470 fb$^{-1}$ of data collected at or near the $\Upsilon(4S)$ resonance, with the $BABAR$ detector at the PEP II $e^+e^-$ collider.
We measure $\mathcal{B}(D^0\to K^-\pi^+e^-e^+) = (4.0\pm0.5)\times 10^{-6}$ in the di-lepton mass range $0.675< m(e^+e^-) < 0.875$ GeV$/c^{2}$, where the production of the intermediate state $\rho \to e^+e^-$ dominates, and set upper limits for decays outside this interval where long-distance effects are expected to be small. The result in the $\rho \to e^+e^-$ region is consistent with the recent observation of the analogous $D^0\to K^-\pi^+\mu^+\mu^-$ decay, reported by the LHCb Collaboration.
