Search for the Flavor-Changing Neutral Current Decay $D^0 \to \mu^+\mu^-$ with the HERA-B Detector

TL;DR

This paper reports a search for the rare decay $D^0 o $ using HERA-B data, setting an upper limit on its branching fraction due to no observed evidence.

Contribution

The study provides the first upper limit on the branching fraction of $D^0 o $ decay with a large dataset, constraining new physics models.

Findings

No evidence for $D^0 o $ decay was observed.

Set a 90% confidence level upper limit on the branching fraction at $2.0 imes 10^{-6}$.

Analyzed 50 million events from 920 GeV proton interactions.

Abstract

We report on a search for the flavor-changing neutral current decay $D^0 \to \mu^+\mu^-$ using $50 \times 10^6$ events recorded with a dimuon trigger in interactions of 920 GeV protons with nuclei by the HERA-B experiment. We find no evidence for such decays and set a 90% confidence level upper limit on the branching fraction $Br(D^0 \to \mu^+\mu^-) <2.0 \times 10^{-6}$.