Searches for Rare or Forbidden Semileptonic Charm Decays

TL;DR

This study searches for rare charm hadron decays involving leptons, setting new upper limits on their branching fractions, with no significant signals found, thus constraining new physics models beyond the Standard Model.

Contribution

First comprehensive search for 35 rare charm semileptonic decays using BaBar data, establishing new upper limits and improving existing constraints.

Findings

No significant signals observed in any decay mode.

Established upper limits on branching fractions between 10^{-6} and 44×10^{-6}.

Most results are first limits or significantly improved constraints.

Abstract

We present searches for rare or forbidden charm decays of the form $X_c^+\to h^\pm\ell^\mp\ell^{(\prime)+}$, where $X_c^+$ is a charm hadron ($D^+$, $D^+_s$, or $\Lambda_c^+$), $h^\pm$ is a pion, kaon, or proton, and $\ell^{(\prime)\pm}$ is an electron or muon. The analysis is based on $384 fb^{-1}$ of $e^+e^-$ annihilation data collected at or close to the $\Upsilon(4S)$ resonance with the BaBar detector at the SLAC National Accelerator Laboratory. No significant signal is observed for any of the 35 decay modes that are investigated. We establish 90% confidence-level upper limits on the branching fractions between $1 \times 10^{-6}$ and $44 \times 10^{-6}$ depending on the channel. In most cases, these results represent either the first limits or significant improvements on existing limits for the decay modes studied.