Measurement of the Higgs boson production in association with a ttbar pair in the Higgs to diphoton decay channel, and search for the dimuon decay of the Higgs boson in pp collisions at a center-of-mass energy of 13 TeV with the ATLAS detector

This poster describes a measurement of the Higgs boson production in association with a ttbar pair (ttH production) in the Higgs to diphoton decay channel, and a search for the dimuon decay of the Higgs boson. Both analyses use data of pp collisions at a center-of-mass energy of 13 TeV collected with the ATLAS detector at the Large Hadron Collider. The first analysis selects events with 2 photons and at least one b-tagged jet, while the second analysis selects events with 2 muons. Both analyses split events to categories with machine learning techniques. In each of the two analyses, a simultaneous fit in the event categories is performed to extract the signal. In the measurement of the ttH production in the Higgs to diphoton decay channel, the signal-to-background ratios of the event categories range from 160% to 5%. The expected and observed significances of the signal process are evaluated: the ttH production is observed in the diphoton decay model of the Higgs boson. The ttH cross section times the Higgs to diphoton branching ratio is also measured. In the search for the dimuon decay of the Higgs boson, the signal-to-background ratios of the event categories are much smaller. The signal strength (defined as the ratio of the observed signal yield to the one expected in the Standard Model) is measured. The expected and observed upper limits on the signal strength are also evaluated at 95% confidence level.