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

TL;DR

The paper reports a CMS search for Higgs boson production in association with a top-quark pair (ttH) using 7 and 8 TeV data, combining H decays to bb, γγ, and WW/ZZ/ττ to directly probe the top Yukawa coupling. It employs a suite of channel-specific selections and multivariate analyses (including BDTs) to maximize sensitivity across all ttH signatures, with detailed data/MC corrections and a comprehensive treatment of systematic uncertainties. The combined result shows a best-fit signal strength μ ≈ 2.8 with about ±1.0 accuracy, corresponding to a local significance of 3.4σ, hinting at an excess over background but overall consistent with SM ttH production within uncertainties. This work provides a direct constraint on the top–Higgs coupling and demonstrates the feasibility of multi-channel ttH measurements at the LHC.

Abstract

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.

Figures (15)

• Figure 1: Feynman diagrams showing the gluon fusion production of a Higgs boson through a top-quark loop (left), the decay of a Higgs boson to a pair of photons through a top-quark loop (center), and the production of a Higgs boson in association with a top-quark pair (right). These diagrams are representative of SM processes with sensitivity to the coupling between the top quark and the Higgs boson.
• Figure 2: Input variables that give the best signal-background separation for each of the lepton+jets categories used in the analysis at $\sqrt{s} = 8\,\text{Te\spaceV}\xspace$. The top, middle, and bottom rows show the events with 4, 5, and $\ge$6 jets, respectively, while the left, middle, and right columns are events with 2, 3, and $\ge$4 b-tags, respectively. More details regarding these plots are found in the text.
• Figure 3: Input variables that give the best signal-background separation for each of the dilepton categories used in the analysis at $\sqrt{s} = 8\,\text{Te\spaceV}\xspace$. The left, middle, and right panels show the events with 3 jets and 2 b-tags, $\ge$4 jets and 2 b-tags, and $\ge$3 b-tags, respectively. More details regarding these plots are found in the text.
• Figure 4: Examples of input variables that give the best signal-background separation in the analysis of the $\tau_\mathrm{h}\xspace$ channels at $\sqrt{s} = 8\,\text{Te\spaceV}\xspace$. The left plot shows the $p_{\mathrm{T}}\xspace$ of the more energetic $\tau_\mathrm{h}\xspace$, while the right plot displays $M_\mathrm{vis}$, the mass of the visible $\tau_\mathrm{h}\xspace$ decay products. Events of all categories are shown. More details regarding these plots are found in the text.
• Figure 5: Final BDT output for lepton+jets events. The top, middle and, bottom rows are events with 4, 5, and $\ge$6 jets, respectively, while the left, middle, and right columns are events with 2, 3, and $\ge$4 b-tags, respectively. Details regarding signal and background normalizations are described in the text.