Search for decays of the Higgs boson into pair-produced pseudoscalar particles decaying into tau+ tau− tau+ tau− using pp collisions at root s =13 TeV with the ATLAS detector

A search for a pair of low-mass pseudoscalars (Formula presented) (Formula presented) that promptly decay into (Formula presented) (Formula presented) -leptons is presented using 140 fb (Formula presented) (Formula presented) of proton–proton collision data at (Formula presented) (Formula presented) 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 (Formula presented) (Formula presented) -leptons, (Formula presented) (Formula presented). This search focuses on events with either one or two (Formula presented) (Formula presented) -leptons decaying into hadrons and neutrinos, and the remaining three or two (Formula presented) (Formula presented) -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 (Formula presented) (Formula presented) are set ranging from 0.06 to 0.23, depending on the mass (Formula presented) (Formula presented) ranging from 15 to 60 GeV.