Direct probes of flavor-changing neutral currents in $e^{+}{e}^{-}$ collisions

Abstract

We propose a novel method to study flavor-changing neutral currents in the $e^{+}{e}^{-}\to D^{\ast 0}$ and $e^{+}{e}^{-}\to B_s^{\ast }$ transitions, tuning the energy of $e^{+}{e}^{-}$- collisions to the mass of the narrow vector resonance $D^{\ast 0}$ or $B_s^{\ast }$. We present a thorough study of both short-distance and long-distance contributions to $e^{+}{e}^{-}\to D^{\ast 0}$ in the Standard Model and investigate possible contributions of new physics in the charm sector. This process, albeit very rare, has clear advantages with respect to the $D^0\to e^{+}{e}^{-}$ decay: the helicity suppression is absent, and a richer set of effective operators can be probed. Implications of the same proposal for $B_s^{\ast }$ are also discussed.

Comments: 24 pages, 2 figures