# $B_s\to\mu^+\mu^-$ as current and future probe of new physics

## TL;DR

This paper analyzes how measurements of the rare decay $B_s\to\mu^+\mu^-$ can serve as a powerful probe for new physics, especially in distinguishing different models through future precise asymmetry measurements.

## Contribution

It provides a comprehensive analysis of the constraints on new physics from $B_s\to\mu^+\mu^-$, emphasizing the potential of future asymmetry measurements to differentiate models like MSSM and leptoquarks.

## Key findings

- Future measurements of the mass-eigenstate rate asymmetry can distinguish between new physics models.
- The decay $B_s\to\mu^+\mu^-$ offers complementary information to direct searches.
- The analysis is based on the open source code flavio, ensuring transparency and reproducibility.

## Abstract

The rare flavour-changing neutral current decay $B_s\to\mu^+\mu^-$ is among the most important indirect probes of new physics at the LHC, as it is strongly suppressed in the Standard Model, very sensitive to new physics effects, and theoretically exceptionally clean. We present a thorough state-of-the-art analysis of the constraints on new physics from present and future measurements of this decay, focusing on scalar operators. We show model-independently and in concrete new physics models, namely the MSSM and two leptoquark scenarios, that a future precise measurement of the mass-eigenstate rate asymmetry in $B_s\to\mu^+\mu^-$ would allow to disentangle new physics scenarios that would be indistinguishable based on measurements of the branching ratio alone. We also highlight the complementarity between $B_s\to\mu^+\mu^-$ and direct searches in both model classes. Our numerics is based on the open source code flavio and is made publicly available.