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

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CMS Collaboration

High Energy Physics - Experiment · Submitted 7 Aug 2014 · 91 references

Pith's verdict: A mature six-channel CMS ttH combination whose 3.4σ excess is honestly traced to a same-sign dimuon subsample sitting on a non-prompt background extrapolated from low-jet control regions.

T0 · AI review

How this review was made: An AI referee (selfhosted/deepseek-v4.1-flash) read the paper on October 29, 2026 and answered a fixed list of questions about it. T0 is the starting level every paper gets. The levels describe how deeply Pith has checked the paper, never the authors.

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arXiv ID1408.1682 (version 2)
Pith IDIKTSSYI2, Pith's permanent record of this paper and its review
CitationCMS Collaboration. "Search for the associated production of the Higgs boson with a top-quark pair." arXiv:1408.1682 (2014). https://pith.science/paper/IKTSSYI2
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The paper

The paper claims

A first direct handle on how strongly the Higgs boson couples to the top quark: the CMS search for a Higgs produced alongside a top-quark pair reports a combined signal strength of $2.8$ times the standard-model rate.

The reading

The Higgs boson's coupling to the top quark is expected to be the strongest fermion coupling in the standard model, of order one, but it cannot be measured from Higgs decays because the top quark is heavier than the Higgs. The only direct route is to catch a Higgs boson made in the same event as a top-quark pair, a process roughly 130 fb in cross section at 8 TeV, and count it. This paper combines six such searches at the LHC — Higgs decaying to bottom quarks, to hadronic taus, to photon pairs, and to W, Z, or tau pairs giving two same-sign leptons, three leptons, or four leptons — into one fit for a single number, the ratio $~mu = ~sigma/~sigma_{~text{SM}}$ of the observed rate to the standard-model prediction. The fit returns $~mu = 2.8^{+1.0}_{-0.9}$ at a Higgs mass of 125.6 GeV, which is a 3.4-standard-deviation excess over the background-only hypothesis against an expected 1.2 standard deviations, and is also a roughly two-standard-deviation upward fluctuation relative to the standard model. If it holds up, this is the first experimental evidence that the Higgs boson is produced together with top quarks, and therefore the first direct measurement of the top-quark Yukawa coupling.

What carries the argument

The load-bearing device is a single binned likelihood over all channels in which every source of systematic uncertainty enters as a nuisance parameter, correlated across channels where the source is common, and the parameter of interest is the one number $~mu$. Each channel contributes a discriminating distribution rather than a yield: boosted decision trees trained on kinematics, event shape, and b-tagging output for the hadronic and leptonic channels, and the diphoton invariant mass for the photon channel, where the background shape is fitted from the data itself with the choice of functional form carried as a discrete nuisance parameter. Two data-driven estimates carry particular weight: the non-prompt lepton background in the multilepton channel, obtained by weighting events that fail the lepton multivariate discriminant by measured misidentification probabilities, and the charge-misidentification background from opposite-sign dilepton events reweighted by per-lepton charge-flip probabilities. The photon channel also requires an explicit accounting of Higgs production modes other than $t~bar t H$, which would peak at the same mass and are therefore estimated and assigned an uncertainty rather than neglected.

Extended reading notes

Core claim

The paper's claim is that a combined search across the main Higgs decay signatures has established, at the level of 3.4 standard deviations over background, the associated production of a Higgs boson with a top-quark pair. The data are up to 19.7 fb$^{-1}$ at 8 TeV and 5.1 fb$^{-1}$ at 7 TeV, and the six sub-channels are fitted simultaneously for a common signal strength with standard-model Higgs branching fractions assumed. The result is $~mu = 2.8^{+1.0}_{-0.9}$ at 68% confidence level for $m_H = 125.6$ GeV, with a background-only $p$-value of 0.04% and a $p$-value of 2.0% under the standard-model hypothesis $~mu = 1$. The observed 95% confidence upper limit is $~mu < 4.5$, against a median expected limit of 1.7 without signal and 2.7 assuming standard-model $t~bar t H$ production. The authors are explicit that the excess is not uniform: the same-sign dilepton channel gives the largest signal strength, driven by the same-sign dimuon subsample at $~mu = 8.5^{+3.3}_{-2.7}$, and removing that subsample lowers the combined fit to $~mu = 1.9^{+1.0}_{-0.9}$ with a 2.2-standard-deviation significance, while the internal consistency of the six channel results with a common strength is 29%. A two-parameter fit that scales Higgs couplings to vector bosons and to fermions separately gives a best point of $(~kappa_V, ~kappa_f) = (2.2, 1.5)$, compatible with the standard-model $(1,1)$ at 95% confidence level.

Load-bearing premise

The result rests on the multilepton channel's data-driven estimate of background events containing a non-prompt lepton, which is measured in control samples with fewer jets and extrapolated to the four-or-more-jet signal region; if that extrapolation is wrong, the excess moves.

Editorial extensions

If this is right

  • A confirmed $t~bar t H$ signal would give the first direct, tree-level measurement of the top-quark Yukawa coupling, rather than the indirect constraint that comes from the top-quark loop in gluon fusion and in Higgs-to-photon decays.
  • The measured rate can be recast as a constraint on models with heavy top-quark partners, which would decay to a top quark and a Higgs boson and would shift the $t~bar t H$ rate away from the standard-model prediction.
  • The same data constrain the sign and size of new physics in the Higgs coupling to fermions versus vector bosons, as the two-parameter $(~kappa_V, ~kappa_f)$ scan already demonstrates.
  • The analysis strategy — many weak decay channels combined into one fit with correlated nuisances, plus data-driven estimates of the dominant reducible backgrounds — sets the template for the higher-statistics $t~bar t H$ measurements that follow.
  • The observed upper limit of 4.5 on $~mu$ bounds any beyond-standard-model enhancement of $t~bar t H$ plus extra jets at the 8 TeV collision energy.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • The significance arithmetic is the part most sensitive to how the dominant reducible backgrounds are extrapolated: the multilepton channel's non-prompt estimate is measured in low-jet control samples and applied to events with four or more jets, so an unmodelled jet-multiplicity dependence in the misidentification rate would move the combined $~mu$ more than any single detector systematic.
  • Because the same-sign dimuon subsample carries the excess, an independent check with a different dimuon background decomposition — for example a looser lepton selection with the misidentification rate measured directly in the signal-like jet multiplicity — would be the cheapest way to confirm or dissolve the result.
  • The internal consistency of 29% across six channels is not alarming on its own, but combined with the concentration of the excess in one subsample it suggests the fit is being pulled by a single region rather than by a coherent signal across decay modes, which is what a genuine $t~bar t H$ signal would be expected to produce.
  • If the effect is real, the same analysis applied to the larger 13 TeV dataset should show the excess grow roughly in proportion to the $t~bar t H$ cross section, which rises steeply with collision energy — a much sharper test than repeating the 8 TeV measurement.
Original 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.

The compiled record

The paper's own sentences, arranged, kept beside the review and separate from it. Each label is drawn from a closed vocabulary; the number beside it is the probability the classifier gave that label. Numbers in the tables are the authors', checked by code. No sentence in this record was written by a model.

Compiled by classifier-1.13-20260917 via OpenRouter, question bank abstract-p1-20260923, 2026-09-23: 1 request, 3,800 input tokens, $0.0002 reported.

What the abstract itself states, as probabilities: claims first 0.03 · states limitation 0.25 · human participants 0.02 · controlled comparison 0.30 · randomized assignment 0.01 · states quantitative result 0.99 · compares with prior results 0.55 · mentions code or data availability 0.02.

The abstract, sentence by sentence

arXiv listing abstract v2. Results and the main claim are underlined; .

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.

background contribution method result interpretation main claim

What the classifier reports for each sentence. The number is the probability it gave the label.
#sentencerolethe authors' own workstates the main conclusionstrength
s0 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. method 0.50 0.91 0.03 asserted 0.90
s1 The search is based on the following signatures of the Higgs boson decay: H to hadrons, H to photons, and H to leptons. method 0.97 0.55 0.02 asserted 0.98
s2 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. method 0.75 0.74 0.07 asserted 0.91
s3 The best fit value is mu = 2.8 +/- 1.0 for a Higgs boson mass of 125.6 GeV. result 1.00 0.96 0.79 asserted 1.00

What kind of paper the classifier reports this is: empirical study 1.00 · evidence from observation or experiment 0.71.

What was examined, and what was not

sources read
  • arXiv listing abstract v2
not examined
  • full text
  • figures and tables
  • references and citing sentences
  • relations to other papers
levels run
  • P abstract
not run
  • S sections
  • T body sentences
  • C citations
  • R cross-paper relations

Every quoted sentence on this record is the authors'. Every label is from Pith's closed vocabulary, with the probability shown beside it. Every number in the measurements table is the authors', checked by code. Record as JSON

Figures
Figure 1. Feynman diagrams showing the gluon fusion production of a Higgs boson through
Figure 2. Input variables that give the best signal-background separation for each of the lep
Figure 3. Input variables that give the best signal-background separation for each of the dilep
Figure 4. Examples of input variables that give the best signal-background separation in the
Figure 5. Final BDT output for lepton+jets events. The top, middle and, bottom rows are events
Figure 6. Final BDT output for dilepton events. The upper left, upper right, and lower left
Figure 7. Final BDT output for events in the τh channel. The top row is the 2 jet categories, while the second and third rows are for the categories with 3 jets and ≥4 jets, respectively. In each row, the columns are for the categories with 1 b-tag (left) and 2 b-tags (right). Details regarding signal and background normalizations are described in the text
Figure 8. Distributions of the b-tagged jet multiplicity (top row) and jet multiplicity (bottom
Figure 9. Diphoton invariant mass distribution for
Figure 10. These plots show the distribution of key discriminating variables for events where
Figure 11. Distribution of the jet multiplicity (top row) and the BDT discriminant (bottom row)
Figure 12. Distribution of the jet multiplicity (left) and BDT discriminant (center) for the trilep
Figure 13. Left: The best-fit values of the signal strength parameter
Figure 14. The 2D test statistic q(κV, κf ) scan vs. the modifiers to the coupling of the Higgs boson to vector bosons (κV) and fermions (κf ), profiling all other nuisances, extracted using only the ttH analysis channels. The contour lines at 68% CL (solid line) and 95% CL (dashed line) are shown. The best-fit and SM predicted values of the coupling modifiers (κV, κf ) are given by the black cross and the open diamond, respectively. (GeV) mH 110 115 120 125 130 135 140 SM σ / σ 95% CL limit on 0 1 2 3 4 5 6 7 8 9 Observed Expected (sig. inj.) Expected ± 1σ Expected ± 2σ CMS -1 s = 8 TeV,…
Figure 15. The 95% CL upper limits on the signal strength parameter

Figures reproduced from arXiv:1408.1682 by the authors.

References
How later papers used it

92 later papers cite it

Evidence: substantial. 70 of the citing papers share no author with it, and 27 of those carry a confident label from Pith's citation classifier.

Pith read 19 of the 154 citing sentences, choosing only those whose citation markers point at this paper alone, and wrote the paraphrases from them. The summary, the counts, the evidence level, the links and the quotes come from code; the summary counts the papers listed below. A later paper is listed under a label when Pith's citation classifier gives one of its sentences that label at probability 0.8 or more (0.95 for support), Pith's reading finds that the citing paper itself did it, and a second check confirms the paraphrase against the sentence. This section lists uses only. It does not list criticism or disagreement, so their absence here says nothing about how the paper has been received. Papers that share an author with this one are listed apart, under "By the same authors". A quote is the citing authors' own sentence, shown when their paper's licence is CC BY, CC BY-SA or CC0. JSON

Uses its method or tool 3 of 14 papers with this label
Uses its data or values 2 of 26 papers with this label · 1 by the same authors

By the same authors

How the literature uses it

88 arXiv papers cite this in 145 sentences

Each citing sentence is taken from the citing paper's LaTeX source and typed by Pith's classifier. A label appears at probability 0.8 or more (0.95 for support), a contest at 0.7 or more; the quoted words are the citing authors'. How each label was checked · JSON

Papers citing it · 82 sentences without a confident label

Uses its method or tool 14 papers
Uses its data or values 26 papers
  • Here, we averaged the ATLAS [ref] and CMS [ref] results for the Higgs signal strength to fermions $μ_f≡σ/σ_SM _ff̅/_ ff̅^SM$. $σ$ stands for the production cross section, $_X=(h→X)$ and the SM script indicates the SM case.

    Constraining the Charm Yukawa and Higgs-quark Coupling Universality · Introduction · 1.00

  • Here the index $i$ runs over the relevant experimental constraints in Table [ref]. * Signal strength measurements from Tevatron [ref] , ATLAS [ref] and CMS [ref] as implemented in Lilith v1.1 (with data version 15.09) [ref] represent the second part of the data set.

    Testing Higgs boson scenarios in the phenomenological NMSSM · Experimental constraints and fit procedure · 0.89

  • At 8 TeV, the uncertainties in $$ measurements are too large to offer any indication of an excess or lack thereof [One notable exception is the CMS measurement in the same-sign dilepton channel [ref] , which gives the following best fit for the signal strength: $μ_ttH=5.3^+2.1_-1.8$ .], with a combined best fit of $μ_ttH=2.3^+0.7_-0.6$ (ATLAS + CMS, all channels) [ref] .

    Charged Higgs Signals in $t\,\overline{t}\,H$ Searches · Signals in Searches · 0.93

Compares with it 3 papers
Cites it as background 15 papers

What it cites · 48 sentences without a confident label

Uses the method or tool of 27 papers
Uses data or values from 11 papers
Cites as background 3 papers

Discussion

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