Search for Resonant and Nonresonant Higgs Boson Pair Production in the b(b)over-bar tau(+) tau(-) Decay Channel in pp Collisions at root s=13 TeV with the ATLAS Detector

A search for resonant and nonresonant pair production of Higgs bosons in the 𝑏⁢ ¯ 𝑏 ⁢𝜏+⁢𝜏− final state is presented. The search uses 36.1  fb−1 of 𝑝⁢𝑝 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<𝑚𝑋<402  GeV in the simplified hMSSM minimal supersymmetric model for tan⁡𝛽 =2 and excluding bulk Randall-Sundrum gravitons 𝐺KK in the mass range 325  GeV<𝑚𝐺KK<885  GeV for 𝑘/ ¯ 𝑀 Pl=1.