Measurement of the top-Yukawa coupling and the search for ttH production

To test whether the observed Higgs boson follows the predictions of the SM, careful study and measurement of its properties are necessary. Due to the top quark's large mass, a measurement of the top-Yukawa coupling (Y_t) is paramount to an understanding of EWSB and could provide a viable probe for new physics. While most production processes provide only an indirect measurement of Y_t via loop effects, the ttH and tH production allow for a direct tree-level measurement of the coupling strength (which could differ due to new physics contamination). The ttH process is probed through various Higgs decay channels with several advantages. The H->bb channel allows for a coupling measurement of both 3rd generation quarks while profiting from the largest Higgs branching ratio. The h->γγ channel has a much smaller branching ratio but benefits from a fine diphoton mass resolution. The process is also probed in the multilepton channel, which is targeted at the off-shell Higgs coupling of H->WW* and H->ZZ* as well as the coupling to a third generation fermion from H->ττ. The measurement of Y_t is also extended to include a measurement of the sign of the coupling through tH production, which is suppressed in the SM but enhanced in the presence of new physics where relative sign of the top and W couplings to the Higgs boson is opposite to that of the Standard Model.