  A search for the standard model Higgs boson produced in association with a
top-quark pair (t tbar H) is presented, using data samples corresponding to
integrated luminosities of up to 5.1 inverse femtobarns and 19.7 inverse
femtobarns 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 to hadrons, H to photons, and H to leptons. The results are
characterized by an observed t tbar H signal strength relative to the standard
model cross section, mu = sigma/sigma[SM], under the assumption that the Higgs
boson decays as expected in the standard model. The best fit value is mu = 2.8
+/- 1.0 for a Higgs boson mass of 125.6 GeV.
