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 → ττ 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 ffiffi s p ¼ 13 TeV. All combinations of leptonic (τ → lvv¯ with l ¼ e; μ) and hadronic (τ → hadrons v) τ decays are considered. The H → ττ 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 → ττ decays. Using the data taken at ffiffi s p ¼ 13 TeV, the total cross section in the H → ττ decay channel is measured to be 3.77þ0.60 −0.59 ðstatÞ þ0.87 −0.74 ðsystÞ 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 → ττ decay channel are determined separately for vector-boson-fusion production and gluon-gluon-fusion production to be σVBF H→ττ ¼ 0.28 0.09 ðstatÞ þ0.11 −0.09 ðsystÞ pb and σggF H→ττ ¼ 3.1 1.0 ðstatÞ þ1.6 −1.3 ðsystÞ 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.