A search for a standard model Higgs boson produced in association with a top-quark pair and decaying to bottom quarks is presented. Events with hadronic jets and one or two oppositely charged leptons are selected from a data sample corresponding to an integrated luminosity of 19.5 inverse femtobarns collected by the CMS experiment at the LHC in pp collisions at a centre-of-mass energy of 8 TeV. In order to separate the signal from the larger t t-bar + jets background, this analysis uses a matrix element method that assigns a probability density value to each reconstructed event under signal or background hypotheses. The ratio between the two values is used in a maximum likelihood fit to extract the signal yield. The results are presented in terms of the measured signal strength modifier, mu, relative to the standard model prediction for a Higgs boson mass of 125 GeV. The observed (expected) exclusion limit at a 95% confidence level is mu < 4.2 (3.3), corresponding to a best fit value mu-hat = 1.2 +1.6 -1.5.
CMS, Basegmez, S., Beluffi, C., Bruno, G., Castello, R., Caudron, A., Ceard, L., Da Silveira, G. G., Delaere, C., Du Pree, T., Favart, D., Forthomme, L., Giammanco, A., Hollar, J., Jafari, A., Jez, P., Komm, M., Lemaitre, V., Nuttens, C., et al. (2015). Search for a standard model Higgs boson produced in association with a top-quark pair and decaying to bottom quarks using a matrix element method. European Physical Journal C. Particles and Fields, C75, 251. https://doi.org/10.1140/epjc/s10052-015-3454-1 (Original work published 2015)