# Search for light pseudoscalar boson pairs produced from decays of the 125 GeV Higgs boson in final states with two muons and two nearby tracks in pp collisions at $\sqrt{s} =$ 13 TeV

## TL;DR

This study searches for pairs of light pseudoscalar bosons from Higgs decays in proton-proton collisions at 13 TeV, focusing on final states with muons and tau leptons, setting limits on their production without observing a significant signal.

## Contribution

It provides the first combined search for light pseudoscalar pairs in the 4-15 GeV range using 13 TeV data, constraining their production and decay properties.

## Key findings

- No significant excess observed beyond Standard Model expectations.
- Upper limits on production cross section times branching ratio range from 0.022 to 0.23.
- Constraints improve understanding of Higgs decays to light pseudoscalars.

## Abstract

A search is presented for pairs of light pseudoscalar bosons, in the mass range from 4 to 15 GeV, produced from decays of the 125 GeV Higgs boson. The decay modes considered are final states that arise when one of the pseudoscalars decays to a pair of tau leptons, and the other one either into a pair of tau leptons or muons. The search is based on proton-proton collisions collected by the CMS experiment in 2016 at a center-of-mass energy of 13 TeV that correspond to an integrated luminosity of 35.9 fb${-1}$. The 2$\mu$2$\tau$ and 4$\tau$ channels are used in combination to constrain the product of the Higgs boson production cross section and the branching fraction into 4$\tau$ final state, $\sigma\mathcal{B}$, exploiting the linear dependence of the fermionic coupling strength of pseudoscalar bosons on the fermion mass. No significant excess is observed beyond the expectation from the standard model. The observed and expected upper limits at 95% confidence level on $\sigma\mathcal{B}$, relative to the standard model Higgs boson production cross section, are set respectively between 0.022 and 0.23 and between 0.027 and 0.19 in the mass range probed by the analysis.