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CMS-PAS-HIG-17-005
Search for production of a Higgs boson and a single top quark in multilepton final states in proton collisions at √s= 13 TeV
CMS Collaboration
May 2017
Abstract: A search for the production of a Higgs boson in association with a single top quark is presented, focusing on leptonic signatures provided by the H→WW, H→ττ, and H→ZZ decay modes. Due to strong interference of the two main leading-order diagrams, the production cross section of this process is highly sensitive to the relative sign of the top-Higgs coupling modifier, κt, and the coupling modifier of vector bosons to the Higgs, κV. The analysis exploits signatures with two same-sign leptons or three leptons in the final state, and uses the 2016 data sample collected with the CMS detector at the LHC at a center of mass energy of 13 TeV, which corresponds to an integrated luminosity of 35.9 fb−1. Multivariate techniques are used to discriminate the signal from the dominant backgrounds. The analysis yields a 95% confidence level (C.L.) upper limit on the combined tH+t¯tH production cross section times branching ratio of 0.64 pb, with an expected limit of 0.32 pb, for a scenario with κt=−1.0 and κV=1.0. Values of κt outside the range of −1.25 to +1.60 are excluded at 95% C.L., assuming κV=1.0.
Links: CDS record (PDF) ; inSPIRE record ; CADI line (restricted) ;
Figures & Tables Summary Additional Figures References CMS Publications
Figures

png pdf 		Figure 1:
Dominant leading order Feynman diagrams for the production of tHq events. The Higgs boson is either radiated from the W boson (left) or the top quark (right).

png pdf 		Figure 1-a:
Dominant leading order Feynman diagram for the production of tHq events. The Higgs boson is radiated from the W boson.

png pdf 		Figure 1-b:
Dominant leading order Feynman diagram for the production of tHq events. The Higgs boson is radiated from the top quark.

png pdf 		Figure 2:
Distributions of discriminating variables for the event pre-selection for the same-sign μμ channel, normalized to 35.9 fb−1, before fitting the signal discriminant to the observed data. Uncertainties are statistical and unconstrained (pre-fit) normalization systematics. The shape of the two tH signals for κt=−1.0 is shown, normalized to their respective cross sections for κt=−1.0,κV=1.0.

png pdf 		Figure 2-a:
Distribution for the event pre-selection for the same-sign μμ channel, normalized to 35.9 fb−1, before fitting the signal discriminant to the observed data. Uncertainties are statistical and unconstrained (pre-fit) normalization systematics. The shape of the two tH signals for κt=−1.0 is shown, normalized to their respective cross sections for κt=−1.0,κV=1.0.

png pdf 		Figure 2-b:
Distribution for the event pre-selection for the same-sign μμ channel, normalized to 35.9 fb−1, before fitting the signal discriminant to the observed data. Uncertainties are statistical and unconstrained (pre-fit) normalization systematics. The shape of the two tH signals for κt=−1.0 is shown, normalized to their respective cross sections for κt=−1.0,κV=1.0.

png pdf 		Figure 2-c:
Distribution for the event pre-selection for the same-sign μμ channel, normalized to 35.9 fb−1, before fitting the signal discriminant to the observed data. Uncertainties are statistical and unconstrained (pre-fit) normalization systematics. The shape of the two tH signals for κt=−1.0 is shown, normalized to their respective cross sections for κt=−1.0,κV=1.0.

png pdf 		Figure 3:
Distributions of discriminating variables for the event pre-selection for the same-signeμ channel, normalized to 35.9 fb−1, before fitting the signal discriminant to the observed data. Uncertainties are statistical and unconstrained (pre-fit) normalization systematics. The shape of the two tH signals for κt=−1.0 is shown, normalized to their respective cross sections for κt=−1.0,κV=1.0.

png pdf 		Figure 3-a:
Distribution for the event pre-selection for the same-signeμ channel, normalized to 35.9 fb−1, before fitting the signal discriminant to the observed data. Uncertainties are statistical and unconstrained (pre-fit) normalization systematics. The shape of the two tH signals for κt=−1.0 is shown, normalized to their respective cross sections for κt=−1.0,κV=1.0.

png pdf 		Figure 3-b:
Distribution for the event pre-selection for the same-signeμ channel, normalized to 35.9 fb−1, before fitting the signal discriminant to the observed data. Uncertainties are statistical and unconstrained (pre-fit) normalization systematics. The shape of the two tH signals for κt=−1.0 is shown, normalized to their respective cross sections for κt=−1.0,κV=1.0.

png pdf 		Figure 3-c:
Distribution for the event pre-selection for the same-signeμ channel, normalized to 35.9 fb−1, before fitting the signal discriminant to the observed data. Uncertainties are statistical and unconstrained (pre-fit) normalization systematics. The shape of the two tH signals for κt=−1.0 is shown, normalized to their respective cross sections for κt=−1.0,κV=1.0.

png pdf 		Figure 4:
Distributions of discriminating variables for the event pre-selection for the three lepton channel, normalized to 35.9 fb−1, before fitting the signal discriminant to the observed data. Uncertainties are statistical and unconstrained (pre-fit) normalization systematics. The shape of the two tH signals for κt=−1.0 is shown, normalized to their respective cross sections for κt=−1.0,κV=1.0.

png pdf 		Figure 4-a:
Distribution for the event pre-selection for the three lepton channel, normalized to 35.9 fb−1, before fitting the signal discriminant to the observed data. Uncertainties are statistical and unconstrained (pre-fit) normalization systematics. The shape of the two tH signals for κt=−1.0 is shown, normalized to their respective cross sections for κt=−1.0,κV=1.0.

png pdf 		Figure 4-b:
Distribution for the event pre-selection for the three lepton channel, normalized to 35.9 fb−1, before fitting the signal discriminant to the observed data. Uncertainties are statistical and unconstrained (pre-fit) normalization systematics. The shape of the two tH signals for κt=−1.0 is shown, normalized to their respective cross sections for κt=−1.0,κV=1.0.

png pdf 		Figure 4-c:
Distribution for the event pre-selection for the three lepton channel, normalized to 35.9 fb−1, before fitting the signal discriminant to the observed data. Uncertainties are statistical and unconstrained (pre-fit) normalization systematics. The shape of the two tH signals for κt=−1.0 is shown, normalized to their respective cross sections for κt=−1.0,κV=1.0.

png pdf 		Figure 5:
Pre-fit BDT classifier outputs, for the three-lepton channel (left), eμ (center), and μμ (right), for 35.9 fb−1, for training against tˉtV (top row) and against tˉt (bottom row). In the box below each distribution, the ratio of the observed and predicted event yields is shown. The shape of the two tH signals for κt=−1.0 is shown, normalized to their respective cross sections for κt=−1.0,κV=1.0. The grey band represents the unconstrained (pre-fit) statistical and systematical uncertainties.

png pdf 		Figure 5-a:
Pre-fit BDT classifier output, for the three-lepton channel , for 35.9 fb−1, for training against tˉtV. In the box below the distribution, the ratio of the observed and predicted event yields is shown. The shape of the two tH signals for κt=−1.0 is shown, normalized to their respective cross sections for κt=−1.0,κV=1.0. The grey band represents the unconstrained (pre-fit) statistical and systematical uncertainties.

png pdf 		Figure 5-b:
Pre-fit BDT classifier output, for eμ, for 35.9 fb−1, for training against tˉtV. In the box below the distribution, the ratio of the observed and predicted event yields is shown. The shape of the two tH signals for κt=−1.0 is shown, normalized to their respective cross sections for κt=−1.0,κV=1.0. The grey band represents the unconstrained (pre-fit) statistical and systematical uncertainties.

png pdf 		Figure 5-c:
Pre-fit BDT classifier output, for μμ, for 35.9 fb−1, for training against tˉtV. In the box below the distribution, the ratio of the observed and predicted event yields is shown. The shape of the two tH signals for κt=−1.0 is shown, normalized to their respective cross sections for κt=−1.0,κV=1.0. The grey band represents the unconstrained (pre-fit) statistical and systematical uncertainties.

png pdf 		Figure 5-d:
Pre-fit BDT classifier output, for the three-lepton channel, for 35.9 fb−1, for training against tˉt. In the box below the distribution, the ratio of the observed and predicted event yields is shown. The shape of the two tH signals for κt=−1.0 is shown, normalized to their respective cross sections for κt=−1.0,κV=1.0. The grey band represents the unconstrained (pre-fit) statistical and systematical uncertainties.

png pdf 		Figure 5-e:
Pre-fit BDT classifier output, for eμ, for 35.9 fb−1, for training against tˉt. In the box below the distribution, the ratio of the observed and predicted event yields is shown. The shape of the two tH signals for κt=−1.0 is shown, normalized to their respective cross sections for κt=−1.0,κV=1.0. The grey band represents the unconstrained (pre-fit) statistical and systematical uncertainties.

png pdf 		Figure 5-f:
Pre-fit BDT classifier output, for μμ, for 35.9 fb−1, for training against tˉt. In the box below the distribution, the ratio of the observed and predicted event yields is shown. The shape of the two tH signals for κt=−1.0 is shown, normalized to their respective cross sections for κt=−1.0,κV=1.0. The grey band represents the unconstrained (pre-fit) statistical and systematical uncertainties.

png pdf 		Figure 6:
Post-fit categorized BDT classifier outputs as used in the maximum likelihood fit for the three-lepton channel (left), eμ (center), and μμ (right), for 35.9 fb−1. In the box below each distribution, the ratio of the observed and predicted event yields is shown.

png pdf 		Figure 6-a:
Post-fit categorized BDT classifier outputs as used in the maximum likelihood fit for the three-lepton channel, for 35.9 fb−1. In the box below the distribution, the ratio of the observed and predicted event yields is shown.

png pdf 		Figure 6-b:
Post-fit categorized BDT classifier outputs as used in the maximum likelihood fit for eμ, for 35.9 fb−1. In the box below the distribution, the ratio of the observed and predicted event yields is shown.

png pdf 		Figure 6-c:
Post-fit categorized BDT classifier outputs as used in the maximum likelihood fit for μμ, for 35.9 fb−1. In the box below the distribution, the ratio of the observed and predicted event yields is shown.

png pdf 		Figure 7:
Observed and expected 95% C.L. upper limit on the tH+tˉtH cross section times H→WW∗+ττ+ZZ∗ branching fraction for different values of the coupling ratio κt/κV. The expected limit is derived from a background-only MC dataset.
Tables

png pdf
 Table 1:
Summary of event selection.

png pdf
 Table 2:
Data yields and expected backgrounds after the event pre-selection for the three channels in 35.9 fb−1 of integrated luminosity. Uncertainties are statistical only.

png pdf
 Table 3:
Input variables to the signal discrimination classifier.

png pdf
 Table 4:
Expected and observed 95% C.L. upper limits on the tH+tˉtH production cross section times H→WW∗+ττ+ZZ∗ branching ratio for a scenario of inverted couplings (κt/κV=−1.0, top rows) and for a standard-model-like signal (κt/κV=1.0, bottom rows), in pb. The expected limit is calculated on a background-only MC dataset.
Summary
A search for the production of a Higgs boson in association with a single top quark has been presented, using the CMS detector and the full 2016 data sample of pp collisions at 13 TeV, corresponding to an integrated luminosity of 35.9 fb−1. Three channels have been analyzed, targeting the Higgs boson decaying to a pair of W or Z bosons, or two τ leptons and the leptonic decay of the top: two same-sign leptons (μμ, eμ) and three leptons. This process can benefit from a greatly enhanced production cross section in the case of anomalous top-Higgs couplings, and the results are used to constrain these couplings.

Combining the results from all three channels yields a 95% confidence level (C.L.) upper limit on the production cross section times branching ratio of events containing a SM Higgs boson of 0.56 pb, with an expected limit of 0.24 pb.

Values of the ratio of Higgs-top coupling modifier κt and Higgs-vector boson coupling modifier κV are outside the range −1.25 to +1.60 are excluded at 95% C.L.
Additional Figures

png pdf 		Additional Figure 1:
Pre-fit categorized BDT classifier outputs, for the three-lepton channel (left), eμ (center), and μμ (right), for 35.9 fb−1. In the box below each distribution, the ratio of the observed and predicted event yields is shown. The shape of the two tH signals for κt=−1.0 is shown, normalized to their respective cross sections for κt=−1.0, κV=1.0. The grey band represents the unconstrained (pre-fit) statistical and systematical uncertainties.

png pdf 		Additional Figure 1-a:
Pre-fit categorized BDT classifier outputs, for the three-lepton channel, for 35.9 fb−1. In the box below each distribution, the ratio of the observed and predicted event yields is shown. The shape of the two tH signals for κt=−1.0 is shown, normalized to their respective cross sections for κt=−1.0, κV=1.0. The grey band represents the unconstrained (pre-fit) statistical and systematical uncertainties.

png pdf 		Additional Figure 1-b:
Pre-fit categorized BDT classifier outputs, for eμ, for 35.9 fb−1. In the box below each distribution, the ratio of the observed and predicted event yields is shown. The shape of the two tH signals for κt=−1.0 is shown, normalized to their respective cross sections for κt=−1.0, κV=1.0. The grey band represents the unconstrained (pre-fit) statistical and systematical uncertainties.

png pdf 		Additional Figure 1-c:
Pre-fit categorized BDT classifier outputs, for μμ, for 35.9 fb−1. In the box below each distribution, the ratio of the observed and predicted event yields is shown. The shape of the two tH signals for κt=−1.0 is shown, normalized to their respective cross sections for κt=−1.0, κV=1.0. The grey band represents the unconstrained (pre-fit) statistical and systematical uncertainties.

png pdf 		Additional Figure 2:
Post-fit categorized BDT classifier outputs (on logarithmic scale) as used in the maximum likelihood fit for the three-lepton channel (left), eμ (center), and μμ (right), for 35.9 fb−1. In the box below each distribution, the ratio of the observed and predicted event yields is shown.

png pdf 		Additional Figure 2-a:
Post-fit categorized BDT classifier outputs (on logarithmic scale) as used in the maximum likelihood fit for the three-lepton channel, for 35.9 fb−1. In the box below each distribution, the ratio of the observed and predicted event yields is shown.

png pdf 		Additional Figure 2-b:
Post-fit categorized BDT classifier outputs (on logarithmic scale) as used in the maximum likelihood fit for eμ, for 35.9 fb−1. In the box below each distribution, the ratio of the observed and predicted event yields is shown.

png pdf 		Additional Figure 2-c:
Post-fit categorized BDT classifier outputs (on logarithmic scale) as used in the maximum likelihood fit for μμ, for 35.9 fb−1. In the box below each distribution, the ratio of the observed and predicted event yields is shown.

png pdf 		Additional Figure 3:
Observed and expected 95% C.L. upper limit on the tH+tˉtH cross section times H→WW∗+ττ+ZZ∗ branching fraction for different values of the coupling ratio κt/κV. The expected limit is derived from a MC dataset of SM processes including the contributions from tˉtH and tH expected in the SM.
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