Search for decays of the Higgs boson into pair-produced pseudoscalar particles decaying into $\tau^+\tau^-\tau^+\tau^-$ using $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

TL;DR

This paper reports a search for Higgs boson decays into pairs of low-mass pseudoscalars that decay into four tau leptons, using 13 TeV proton-proton collision data from the ATLAS detector, setting upper limits on such exotic decays.

Contribution

First search to constrain Higgs decays into four tau leptons via pseudoscalars in proton-proton collisions at 13 TeV.

Findings

No significant excess observed over Standard Model background.

Upper limits on branching ratio range from 0.06 to 0.23 depending on pseudoscalar mass.

Constraints improve understanding of Higgs exotic decay modes.

Abstract

A search for a pair of low-mass pseudoscalars $a$ that promptly decay into $\tau$-leptons is presented using 140 fb$^{-1}$ of proton-proton collision data at $13$ TeV centre-of-mass energy recorded with the ATLAS detector at the Large Hadron Collider. The result is used to place constraints on exotic decays of the Higgs boson into four $\tau$-leptons, $H\to aa\to \tau^+\tau^-\tau^+\tau^-$. This search focuses on events with either one or two $\tau$-leptons decaying into hadrons and neutrinos, and the remaining three or two $\tau$-leptons decaying into either electron or muon and neutrinos. No significant excess is observed above the expected Standard Model background and upper limits at the 95% confidence level on $\mathcal{B}(H\rightarrow aa\rightarrow \tau^+\tau^-\tau^+\tau^-)$ are set ranging from 0.06 to 0.23, depending on the mass $m_a$ ranging from 15 to 60 GeV.