Search for ttH production using the Matrix Element Method

A search for Standard Model $\mathrm{t\bar{t}H}$ production in the $\mathrm{H\rightarrow b\overline{b} }$ final state is presented. The measurement of the $\mathrm{t\bar{t}H}$ process plays an important role in Higgs characterization studies since it provides a direct probe of the Higgs Yukawa coupling to fermions, particularly to the top quark. Events with one lepton and at least 5 jets or two leptons and at least 4 jets are selected from $19.5$ fb$^{-1}$ of collision data collected by CMS at $\sqrt{s}=8$ TeV. In order to separate the $\mathrm{t\bar{t}H}$ signal from the larger production of $\mathrm{t\bar{t}+jets}$, this analysis uses a Matrix Element Method that assigns a signal and background probability density to each event in terms of a particular Born-level amplitude. A likelihood ratio of these probability densities is used to extract the signal. The statistical interpretation is presented in the form of 95\% CL exclusion limits on the signal strength modifier $\mu=\sigma/\sigma_{\mathrm{SM}}$ and provides an expected (observed) exclusion limit of $\mu<2.9$ ($3.3$), corresponding to a best-fit value $\hat{\mu}=0.67^{+1.35}_{-1.33}$.