Testing the HyperCP anomaly at LHCb: evidence for the $\Sigma^+ \to p \mu^+ \mu^-$ decay

TL;DR

This paper reports evidence for the rare decay $oldsymbol{ ext{Sigma}^+ o p \, ext{mu}^+ ext{mu}^-}$ at LHCb, measures its branching fraction consistent with the Standard Model, and rules out the HyperCP anomaly at 95% CL.

Contribution

The study provides the first evidence for the $ ext{Sigma}^+ o p \, ext{mu}^+ ext{mu}^-$ decay using LHCb data and clarifies the HyperCP anomaly's non-confirmation.

Findings

Evidence for $ ext{Sigma}^+ o p \, ext{mu}^+ ext{mu}^-$ decay

Branching fraction compatible with Standard Model

HyperCP anomaly excluded at 95 ext% CL

Abstract

A search for $\Sigma^+ \to p \mu^+ \mu^-$ decays with LHCb Run 1 data is presented, yielding an evidence for this decay and a measurement of a branching fraction compatible with the Standard Model. The HyperCP anomaly in the dimuon invariant mass distribution is not confirmed, and its branching fraction central value is excluded at 95\% CL. Prospects for the future of this measurement in LHCb are also presented.