A search for the dimuon decay of the Standard Model Higgs boson with the ATLAS detector

A search for the dimuon decay of the Standard Model (SM) Higgs boson is performed using data corresponding to an integrated luminosity of 139 fb-1 collected with the ATLAS detector in Run 2 pp collisions at vs = 13 TeV at the Large Hadron Collider. The observed (expected) significance over the background-only hypothesis for a Higgs boson with a mass of 125.09 GeV is 2.0s (1.7s ). The observed upper limit on the cross section times branching ratio for pp ? H ? µµ is 2.2 times the SM prediction at 95% confidence level, while the expected limit on a H ? µµ signal assuming the absence (presence) of a SM signal is 1.1 (2.0). The best-fit value of the signal strength parameter, defined as the ratio of the observed signal yield to the one expected in the SM, is µ = 1.2 ± 0.6.