Cross-section measurements of the Higgs boson decaying into a pair of τ-leptons in proton-proton collisions at √s=13 TeV with the ATLAS detector

Abstract

A measurement of production cross sections of the Higgs boson in proton-proton collisions is presented in the H → τ τ decay channel. The analysis is performed using 36.1 fb − 1 of data recorded by the ATLAS experiment at the Large Hadron Collider at a center-of-mass energy of √ s = 13 TeV . All combinations of leptonic ( τ → ℓ v ¯ v with ℓ = e , μ ) and hadronic ( τ → hadrons v ) τ decays are considered. The H → τ τ signal over the expected background from other Standard Model processes is established with an observed (expected) significance of 4.4 (4.1) standard deviations. Combined with results obtained using data taken at 7 and 8 TeV center-of-mass energies, the observed (expected) significance amounts to 6.4 (5.4) standard deviations and constitutes an observation of H → τ τ decays. Using the data taken at √ s = 13 TeV , the total cross section in the H → τ τ decay channel is measured to be 3.7 7 + 0.60 − 0.59 ( stat ) + 0.87 − 0.74 ( syst ) pb , for a Higgs boson of mass 125 GeV assuming the relative contributions of its production modes as predicted by the Standard Model. Total cross sections in the H → τ τ decay channel are determined separately for vector-boson-fusion production and gluon-gluon-fusion production to be σ VBF H → τ τ = 0.28 ± 0.09 ( stat ) + 0.11 − 0.09 ( syst ) pb and σ g g F H → τ τ = 3.1 ± 1.0 ( stat ) + 1.6 − 1.3 ( syst ) pb , respectively. Similarly, results of a fit are reported in the framework of simplified template cross sections. All measurements are in agreement with Standard Model expectations.