Search for the associated production of the Higgs boson with a top-quark pair

A search for the standard model Higgs boson produced in association with a top-quark pair $\left(\mathrm{t}\overline{\mathrm{t}}\mathrm{H}\right)$ is presented, using data samples corresponding to integrated luminosities of up to 5.1 fb$^{−1}$ and 19.7 fb$^{−1}$ collected in pp collisions at center-of-mass energies of 7 TeV and 8 TeV respectively. The search is based on the following signatures of the Higgs boson decay: H → hadrons, H → photons, and H → leptons. The results are characterized by an observed $\mathrm{t}\overline{\mathrm{t}}\mathrm{H}$ signal strength relative to the standard model cross section, μ=σ/σ$_{SM}$,under the assumption that the Higgs boson decays as expected in the standard model. The best fit value is μ = 2.8 ± 1.0 for a Higgs boson mass of 125.6 GeV.