Search for resonant and non-resonant Higgs boson pair production in the bτ⁺τ⁻ decay channel in pp collisions at √s = 13 TeV with the ATLAS detector

A search for resonant and nonresonant pair production of Higgs bosons in the b¯bτ⁺τ⁻ final state is presented. The search uses 36.1  fb⁻¹ of pp collision data with √s=13  TeV recorded by the ATLAS experiment at the LHC in 2015 and 2016. Decays of the τ-lepton pairs with at least one τ lepton decaying to final states with hadrons and a neutrino are considered. No significant excess above the expected background is observed in the data. The cross-section times branching ratio for nonresonant Higgs boson pair production is constrained to be less than 30.9 fb, 12.7 times the standard model expectation, at 95% confidence level. The data are also analyzed to probe resonant Higgs boson pair production, constraining a model with an extended Higgs sector based on two doublets and a Randall-Sundrum bulk graviton model. Upper limits are placed on the resonant Higgs boson pair production cross-section times branching ratio, excluding resonances X in the mass range 305  GeV<mGKK<885  GeV for k/¯MPl=1.