Decay rate and asymmetries of $\Sigma^+\to p\mu^+\mu^-$

TL;DR

This paper revisits the decay $ ext{Sigma}^+ o p \, ext{mu}^+ ext{mu}^-$, providing predictions for its rate and asymmetries, considering both long and short distance effects, and exploring potential new physics contributions.

Contribution

It offers a comprehensive analysis of the decay including uncertainties and proposes a parameterization for new physics effects on asymmetries.

Findings

Decay dominated by long distance physics with large uncertainties

Predictions for decay rate, spectrum, and asymmetries within the standard model

Negligible asymmetries from short distance effects in the standard model

Abstract

The LHCb Collaboration has recently reported evidence for the rare hyperon decay $\Sigma^+\to p\mu^+\mu^-$ that is consistent with the standard model expectation. Motivated by this new result we revisit the calculation of this mode including both long and short distance contributions. In the standard model this mode is completely dominated by long distance physics and thus subject to large uncertainties. We present a range of predictions for the rate, the dimuon invariant mass spectrum, and a muon polarization asymmetry that covers these uncertainties as well as known constraints. We study the interplay between short and long distance contributions which could result in additional asymmetries, but we find that they are negligible within the standard model. We propose a parameterization of these asymmetries in terms of a couple of constants that can arise from new physics.