Search for a scalar dimuon resonance with LHC Run2 data from the ATLAS detector

This analysis presents the search for a Higgs-like Boson decaying into a pair of oppositely charged muons. The invariant mass spectrum of the dimuon system is investigated for a peak above the Z-resonance arising from H → µµ decays. The two considered production mechanisms for the Higgs boson are gluon-gluon fusion (ggF) and vector boson fusion (VBF), the latter featuring two additional jets in its final state. The dominant background arises from the Z/Drell-Yan process. This thesis uses data taken by the ATLAS detector at the LHC during proton-proton collisions at a center of mass energy of 13 TeV in 2015. The amount of data analyzed corresponds to an integrated luminosity of 3.2 fb−1. Events are selected on the basis of their kinematic features into a total of seven regions with enhanced signal contribution. One of the region targets primarily VBF production, while the others are optimized to take advantage of varying mass resolution of the detector. The shape of the background spectrum is studied based on Monte Carlo simulations and a parametrized fit function is developed to describe it. In addition, the shape and normalization of the signal peak for the set of available simulated Higgs mass points is modeled by another parametrized fit function. Interpolating the associated parameters yields signal templates for arbitrary Higgs mass hypotheses. A combined fit of the signal and background model to data is performed in the seven signal regions to extract both the background estimation and the measured signal. No significant excess above the expectation from the Standard Model without the H → µµ decay has been observed in the analyzed data. A 95% confidence exclusion limit is set on the signal strength as a function of Higgs mass in the range between 115 GeV and 145 GeV. This result is re-interpreted as a limit on cross section times branching ratio for the decay of a more general scalar boson decaying into muon pairs.