Evidence for the rare decay $\Sigma^+ \to p \mu^+ \mu^-$

TL;DR

This paper reports evidence for the rare decay $oldsymbol{ ext{Sigma}^+ o p \, ext{mu}^+ ext{mu}^-}$ using LHCb data, observing an excess with 4.1 sigma significance and measuring a branching fraction consistent with the Standard Model.

Contribution

First evidence of the $ ext{Sigma}^+ o p \, ext{mu}^+ ext{mu}^-$ decay at LHCb, with a measured branching fraction aligning with theoretical predictions.

Findings

Observed 4.1 sigma excess over background

Measured branching fraction $(2.2^{+1.8}_{-1.3}) imes 10^{-8}$

No structure in dimuon mass distribution

Abstract

A search for the rare decay $\Sigma^+ \to p \mu^+ \mu^-$ is performed using $pp$ collision data recorded by the LHCb experiment at centre-of-mass energies $\sqrt{s} = 7$ and $8$ TeV, corresponding to an integrated luminosity of $3 fb^{-1}$. An excess of events is observed with respect to the background expectation, with a signal significance of 4.1 standard deviations. No significant structure is observed in the dimuon invariant mass distribution, in contrast with a previous result from the HyperCP experiment. The measured $\Sigma^+ \to p \mu^+ \mu^-$ branching fraction is $(2.2\,^{+\,1.8}_{-\,1.3})\times 10^{-8}$, where statistical and systematic uncertainties are included, which is consistent with the Standard Model prediction.