Characterisation of ttH production at 13 TeV in the multijet topologies with CMS

The associated production of a top quark pair with a Higgs boson (ttH) is very important because, in spite of its small production cross section, it enables the direct measurement of the Yukawa coupling of the Higgs boson to the top quark. The final states of ttH events depend on the specific decay of the top quarks and of the Higgs boson, and different topologies are originated, with or without energetic leptons in the final states. The events studied in this work correspond to an all-jet topology, with some of these jets which might be subject to boost given the large transverse momentum involved. It is therefore essential to classify the final states in terms of the number of "resolved" and "boosted" jets, and for each case different triggers are required. Since the background yields (mainly from top quark-antiquark pairs and QCD multijet production) are much larger than the expected signal, special care needs to be used to reduce them. The event selection is based on multivariate analysis algorithms which can distinguish signal from background events, and boosted jets associated to top quarks, to the Higgs bosons or to generic light quarks, enabling the definition of different event categories. The statistical performance of this analysis is characterised by two essential parameters, the upper limits on the signal strength and the signal significance. The expected upper limits on the signal strength are estimated at 95% confidence level, along with the signal significance, for each category and for the combination of all categories.