Top Quark-antiquark Pair Research Articles

Search for a scalar or pseudoscalar dilepton resonance produced in association with a massive vector boson or top quark-antiquark pair in multilepton events at s=13 TeV

A search for beyond the standard model spin-0 bosons, ϕ, that decay into pairs of electrons, muons, or tau leptons is presented. The search targets the associated production of such bosons with a W or Z gauge boson, or a top quark-antiquark pair, and uses events with three or four charged leptons, including hadronically decaying tau leptons. The proton-proton collision data set used in the analysis was collected at the LHC from 2016 to 2018 at a center-of-mass energy of 13 TeV, and corresponds to an integrated luminosity of 138 fb−1. The observations are consistent with the predictions from standard model processes. Upper limits are placed on the product of cross sections and branching fractions of such new particles over the mass range of 15 to 350 GeV with scalar, pseudoscalar, or Higgs-boson-like couplings, as well as on the product of coupling parameters and branching fractions. Several model-dependent exclusion limits are also presented. For a Higgs-boson-like ϕ model, limits are set on the mixing angle of the Higgs boson with the ϕ boson. For the associated production of a ϕ boson with a top quark-antiquark pair, limits are set on the coupling to top quarks. Finally, limits are set for the first time on a fermiophilic dilaton-like model with scalar couplings and a fermiophilic axion-like model with pseudoscalar couplings. © 2024 CERN, for the CMS Collaboration 2024 CERN

Measurement of the cross section of top quark-antiquark pair production in association with a W boson in proton-proton collisions at sqrt{s} = 13 TeV

The production of a top quark-antiquark pair in association with a W boson ( textrm{t}overline{textrm{t}}textrm{W} ) is measured in proton-proton collisions at a center-of-mass energy of 13 TeV. The analyzed data was recorded by the CMS experiment at the CERN LHC and corresponds to an integrated luminosity of 138 fb−1. Events with two or three leptons (electrons and muons) and additional jets are selected. In events with two leptons, a multiclass neural network is used to distinguish between the signal and background processes. Events with three leptons are categorized based on the number of jets and of jets originating from b quark hadronization, and the lepton charges. The inclusive textrm{t}overline{textrm{t}}textrm{W} production cross section in the full phase space is measured to be 868 ± 40(stat) ± 51(syst) fb. The textrm{t}overline{textrm{t}}textrm{W} + and textrm{t}overline{textrm{t}}textrm{W} − cross sections are also measured as 553 ± 30(stat) ± 30(syst) and 343 ± 26(stat) ± 25(syst) fb, respectively, and the corresponding ratio of the two cross sections is found to be 1.61pm 0.15{left(textrm{stat}right)}_{-0.05}^{+0.07}left(textrm{syst}right) . The measured cross sections are larger than but consistent with the standard model predictions within two standard deviations, and represent the most precise measurement of these cross sections to date.

Measurement of the top quark pole mass using textrm{t}overline{textrm{t}} +jet events in the dilepton final state in proton-proton collisions at sqrt{s} = 13 TeV

A measurement of the top quark pole mass {m}_{textrm{t}}^{textrm{pole}} in events where a top quark-antiquark pair ( textrm{t}overline{textrm{t}} ) is produced in association with at least one additional jet ( textrm{t}overline{textrm{t}} +jet) is presented. This analysis is performed using proton-proton collision data at sqrt{s} = 13 TeV collected by the CMS experiment at the CERN LHC, corresponding to a total integrated luminosity of 36.3 fb−1. Events with two opposite-sign leptons in the final state (e+e−, μ+μ−, e±μ∓) are analyzed. The reconstruction of the main observable and the event classification are optimized using multivariate analysis techniques based on machine learning. The production cross section is measured as a function of the inverse of the invariant mass of the textrm{t}overline{textrm{t}} +jet system at the parton level using a maximum likelihood unfolding. Given a reference parton distribution function (PDF), the top quark pole mass is extracted using the theoretical predictions at next-to-leading order. For the ABMP16NLO PDF, this results in {m}_{textrm{t}}^{textrm{pole}} = 172.93 ± 1.36 GeV.

Search for CP violation using textrm{t}overline{textrm{t}} events in the lepton+jets channel in pp collisions at sqrt{s} = 13 TeV

Results are presented on a search for CP violation in the production and decay of top quark-antiquark pairs in the lepton+jets channel. The search is based on data from proton-proton collisions at sqrt{s} = 13 TeV, collected with the CMS detector, corresponding to an integrated luminosity of 138 fb−1. Possible CP violation effects are evaluated by measuring asymmetries in observables constructed from linearly independent four-momentum vectors of the final-state particles. The dimensionless chromoelectric dipole moment of the top quark obtained from the observed asymmetries is measured to be 0.04 ± 0.10 (stat) ± 0.07(syst), and the asymmetries exhibit no evidence for CP-violating effects, consistent with expectations from the standard model.

Measurements of the inclusive and differential production cross sections of a top-quark\u2013antiquark pair in association with a Z\xa0boson at sqrt{s} = 13\xa0TeV with the ATLAS detector

Measurements of both the inclusive and differential production cross sections of a top-quark–antiquark pair in association with a Z boson (t{bar{t}}Z) are presented. The measurements are performed by targeting final states with three or four isolated leptons (electrons or muons) and are based on sqrt{s} = 13 TeV proton–proton collision data with an integrated luminosity of 139 hbox {fb}^{-1}, recorded from 2015 to 2018 with the ATLAS detector at the CERN Large Hadron Collider. The inclusive cross section is measured to be sigma _{t{bar{t}}Z} = 0.99 pm 0.05 (stat.) pm , 0.08 (syst.) pb, in agreement with the most precise theoretical predictions. The differential measurements are presented as a function of a number of kinematic variables which probe the kinematics of the t{bar{t}}Z system. Both absolute and normalised differential cross-section measurements are performed at particle and parton levels for specific fiducial volumes and are compared with theoretical predictions at different levels of precision, based on a chi ^{2}/ndf and p value computation. Overall, good agreement is observed between the unfolded data and the predictions.

Search for New Resonances Coupling to Third Generation Quarks at CMS

I present an overview of searches for new physics with top and bottom quarks and top quark–antiquark pairs in the final state, using proton–proton collision data collected with the CMS detector at the CERN LHC at a center-of-mass energy of 13 TeV. The results cover non-SUSY-based extensions of the SM, including new heavy gauge bosons, like a $$W^{\prime}$$ boson replicating the features of its standard model counterpart, or excited third generation quarks. We considered both semileptonic and fully-hadronic scenarios. We explore the use of jet substructure techniques to reconstruct highly boosted objects in events, enhancing the sensitivity of these searches.

Measurement of the $$\boldsymbol{t}\bar{\boldsymbol{t}}\boldsymbol{H,H}{\rightarrow}\boldsymbol{b}\bar{\boldsymbol{b}}$$ Decay with Run II Data and Prospects for Run III

The search for the associated production of a Higgs boson with a top quark–antiquark pair with the CMS detector will be presented. Candidate $$t\bar{t}H$$ events are selected with criteria enhancing respectively the dileptonic, semileptonic and fully hadronic decay channels of the $$t\bar{t}$$ system and the decay of the Higgs boson into a bottom quark–antiquark pair ( $$H\rightarrow b\bar{b}$$ ). In order to increase the sensitivity of the search, selected events are split into several categories with different expected signal and background rates. A combined fit of multivariate discriminant templates across all categories and decay channels is performed to extract the result. Results for Run II data will be shown. Prospects for improvements towards Run III will also be discussed.

Search for nonresonant Higgs boson pair production in final states with two bottom quarks and two photons in proton-proton collisions at sqrt{s} = 13 TeV

A search for nonresonant production of Higgs boson pairs via gluon-gluon and vector boson fusion processes in final states with two bottom quarks and two photons is presented. The search uses data from proton-proton collisions at a center-of-mass energy of sqrt{s} = 13 TeV recorded with the CMS detector at the LHC, corresponding to an integrated luminosity of 137 fb−1. No significant deviation from the background-only hypothesis is observed. An upper limit at 95% confidence level is set on the product of the Higgs boson pair production cross section and branching fraction into gamma gamma mathrm{b}overline{mathrm{b}} . The observed (expected) upper limit is determined to be 0.67 (0.45) fb, which corresponds to 7.7 (5.2) times the standard model prediction. This search has the highest sensitivity to Higgs boson pair production to date. Assuming all other Higgs boson couplings are equal to their values in the standard model, the observed coupling modifiers of the trilinear Higgs boson self-coupling κλ and the coupling between a pair of Higgs bosons and a pair of vector bosons c2V are constrained within the ranges −3.3 < κλ< 8.5 and −1.3 < c2V< 3.5 at 95% confidence level. Constraints on κλ are also set by combining this analysis with a search for single Higgs bosons decaying to two photons, produced in association with top quark-antiquark pairs, and by performing a simultaneous fit of κλ and the top quark Yukawa coupling modifier κt.

Evidence for Higgs boson decay to a pair of muons

Evidence for Higgs boson decay to a pair of muons is presented. This result combines searches in four exclusive categories targeting the production of the Higgs boson via gluon fusion, via vector boson fusion, in association with a vector boson, and in association with a top quark-antiquark pair. The analysis is performed using proton-proton collision data at sqrt{s} = 13 TeV, corresponding to an integrated luminosity of 137 fb−1, recorded by the CMS experiment at the CERN LHC. An excess of events over the back- ground expectation is observed in data with a significance of 3.0 standard deviations, where the expectation for the standard model (SM) Higgs boson with mass of 125.38 GeV is 2.5. The combination of this result with that from data recorded at sqrt{s} = 7 and 8 TeV, corresponding to integrated luminosities of 5.1 and 19.7 fb−1, respectively, increases both the expected and observed significances by 1%. The measured signal strength, relative to the SM prediction, is {1.19}_{-0.39}^{+0.40}{left(mathrm{stat}right)}_{-0.14}^{+0.15}left(mathrm{syst}right) . This result constitutes the first evidence for the decay of the Higgs boson to second generation fermions and is the most precise measurement of the Higgs boson coupling to muons reported to date.

Probing the Higgs boson through Yukawa force

The ATLAS and CMS collaborations of the LHC have observed that the Higgs boson decays into the bottom quark-antiquark pair, and have also established that the Higgs coupling with the top quark-antiquark pair is instrumental in one of the modes for Higgs production. This underlines the discovery of the Yukawa force at the LHC. We demonstrate the impact of this discovery on the Higgs properties that are related to the dynamics of electroweak symmetry breaking. We show that these measurements have considerably squeezed the allowed window for new physics contributing to the Higgs couplings with the weak gauge bosons and the third generation quarks. The expected constraints at the HL-LHC and future Higgs factories are also shown. We project these constraints on the parameter space of a few motivated scenarios beyond the Standard Model. We pick them under two broad categories, namely, the composite Higgs and its RS dual, as well as various types of multi-Higgs models. The latter category includes models with singlet scalars, Type I, II and BGL-type two-Higgs doublet models, and models with scalar triplets à la Georgi and Machacek.

Search for supersymmetry in pp collisions at s=13 TeV with 137 fb−1 in final states with a single lepton using the sum of masses of large-radius jets

Results are reported from a search for new physics beyond the standard model in proton-proton collisions in final states with a single lepton; multiple jets, including at least one jet tagged as originating from the hadronization of a bottom quark; and large missing transverse momentum. The search uses a sample of proton-proton collision data at $\sqrt{s} =$ 13 TeV, corresponding to 137 fb$^{-1}$, recorded by the CMS experiment at the LHC. The signal region is divided into categories characterized by the total number of jets, the number of bottom quark jets, the missing transverse momentum, and the sum of masses of large-radius jets. The observed event yields in the signal regions are consistent with estimates of standard model backgrounds based on event yields in the control regions. The results are interpreted in the context of simplified models of supersymmetry involving gluino pair production in which each gluino decays into a top quark-antiquark pair and a stable, unobserved neutralino, which generates missing transverse momentum in the event. Scenarios with gluino masses up to about 2150 GeV are excluded at 95% confidence level (or more) for neutralino masses up to 700 GeV. The highest excluded neutralino mass is about 1250 GeV, which holds for gluino masses around 1850 GeV.

Extraction and validation of a new set of CMS pythia8 tunes from underlying-event measurements

New sets of CMS underlying-event parameters (“tunes”) are presented for the pythia8 event generator. These tunes use the NNPDF3.1 parton distribution functions (PDFs) at leading (LO), next-to-leading (NLO), or next-to-next-to-leading (NNLO) orders in perturbative quantum chromodynamics, and the strong coupling evolution at LO or NLO. Measurements of charged-particle multiplicity and transverse momentum densities at various hadron collision energies are fit simultaneously to determine the parameters of the tunes. Comparisons of the predictions of the new tunes are provided for observables sensitive to the event shapes at LEP, global underlying event, soft multiparton interactions, and double-parton scattering contributions. In addition, comparisons are made for observables measured in various specific processes, such as multijet, Drell–Yan, and top quark-antiquark pair production including jet substructure observables. The simulation of the underlying event provided by the new tunes is interfaced to a higher-order matrix-element calculation. For the first time, predictions from pythia8 obtained with tunes based on NLO or NNLO PDFs are shown to reliably describe minimum-bias and underlying-event data with a similar level of agreement to predictions from tunes using LO PDF sets.

Combined measurements of Higgs boson couplings in proton\u2013proton collisions at sqrt{s}=13,text {Te}text {V}

Combined measurements of the production and decay rates of the Higgs boson, as well as its couplings to vector bosons and fermions, are presented. The analysis uses the LHC proton–proton collision data set recorded with the CMS detector in 2016 at sqrt{s}=13,text {Te}text {V} , corresponding to an integrated luminosity of 35.9{,text {fb}^{-1}} . The combination is based on analyses targeting the five main Higgs boson production mechanisms (gluon fusion, vector boson fusion, and associated production with a mathrm {W} or mathrm {Z} boson, or a top quark-antiquark pair) and the following decay modes: mathrm {H} rightarrow gamma gamma , mathrm {Z}mathrm {Z}, mathrm {W}mathrm {W}, mathrm {tau }mathrm {tau }, mathrm {b} mathrm {b} , and mathrm {mu }mathrm {mu }. Searches for invisible Higgs boson decays are also considered. The best-fit ratio of the signal yield to the standard model expectation is measured to be mu =1.17pm 0.10, assuming a Higgs boson mass of 125.09,text {Ge}text {V} . Additional results are given for various assumptions on the scaling behavior of the production and decay modes, including generic parametrizations based on ratios of cross sections and branching fractions or couplings. The results are compatible with the standard model predictions in all parametrizations considered. In addition, constraints are placed on various two Higgs doublet models.

Measurement of the {mathrm {t}overline{mathrm {t}}} production cross section, the top quark mass, and the strong coupling constant using dilepton events in pp collisions at sqrt{s}=13,text {Te}text {V}

A measurement of the top quark–antiquark pair production cross section sigma _{mathrm {t}overline{mathrm {t}}} in proton–proton collisions at a centre-of-mass energy of 13,text {Te}text {V} is presented. The data correspond to an integrated luminosity of 35.9{,text {fb}^{-1}} , recorded by the CMS experiment at the CERN LHC in 2016. Dilepton events (mathrm {e}^{pm }mathrm {mu }^{{mp }}, mathrm {mu ^+}mathrm {mu ^-}, mathrm {e}^+mathrm {e}^-) are selected and the cross section is measured from a likelihood fit. For a top quark mass parameter in the simulation of m_mathrm {mathrm {t}} ^{mathrm {MC}} = 172.5 ,text {Ge}text {V} the fit yields a measured cross section sigma _{mathrm {t}overline{mathrm {t}}} = 803 pm 2 ,text {(stat)} pm 25 ,text {(syst)} pm 20 ,text {(lumi)} ,text {pb} , in agreement with the expectation from the standard model calculation at next-to-next-to-leading order. A simultaneous fit of the cross section and the top quark mass parameter in the powheg simulation is performed. The measured value of m_mathrm {mathrm {t}} ^{mathrm {MC}} = 172.33 pm 0.14 ,text {(stat)} ,^{+0.66}_{-0.72} ,text {(syst)} ,text {Ge}text {V} is in good agreement with previous measurements. The resulting cross section is used, together with the theoretical prediction, to determine the top quark mass and to extract a value of the strong coupling constant with different sets of parton distribution functions.

Search for mathrm{t}overline{mathrm{t}}mathrm{H} production in the mathrm{H}to mathrm{b}overline{mathrm{b}} decay channel with leptonic mathrm{t}overline{mathrm{t}} decays in proton-proton collisions at sqrt{s}=13 TeV

A search is presented for the associated production of a standard model Higgs boson with a top quark-antiquark pair ( mathrm{t}overline{mathrm{t}}mathrm{H} ), in which the Higgs boson decays into a b quark-antiquark pair, in proton-proton collisions at a centre-of-mass energy sqrt{s}=13 TeV. The data correspond to an integrated luminosity of 35.9 fb−1 recorded with the CMS detector at the CERN LHC. Candidate mathrm{t}overline{mathrm{t}}mathrm{H} events are selected that contain either one or two electrons or muons from the mathrm{t}overline{mathrm{t}} decays and are categorised according to the number of jets. Multivariate techniques are employed to further classify the events and eventually discriminate between signal and background. The results are characterised by an observed mathrm{t}overline{mathrm{t}}mathrm{H} signal strength relative to the standard model cross section, μ = σ/σSM, under the assumption of a Higgs boson mass of 125 GeV. A combined fit of multivariate discriminant distributions in all categories results in an observed (expected) upper limit on μ of 1.5 (0.9) at 95% confidence level, and a best fit value of 0.72 ± 0.24(stat) ± 0.38(syst), corresponding to an observed (expected) signal significance of 1.6 (2.2) standard deviations above the background-only hypothesis.

Measurements of b-jet tagging efficiency with the ATLAS detector using toverline{t} events at sqrt{s}=13 TeV

The efficiency to identify jets containing b-hadrons (b-jets) is measured using a high purity sample of dileptonic top quark-antiquark pairs ( toverline{t} ) selected from the 36.1 fb−1 of data collected by the ATLAS detector in 2015 and 2016 from proton-proton collisions produced by the Large Hadron Collider at a centre-of-mass energy sqrt{s}=13 TeV. Two methods are used to extract the efficiency from toverline{t} events, a combinatorial likelihood approach and a tag-and-probe method. A boosted decision tree, not using b-tagging information, is used to select events in which two b-jets are present, which reduces the dominant uncertainty in the modelling of the flavour of the jets. The efficiency is extracted for jets in a transverse momentum range from 20 to 300 GeV, with data-to-simulation scale factors calculated by comparing the efficiency measured using collision data to that predicted by the simulation. The two methods give compatible results, and achieve a similar level of precision, measuring data-to-simulation scale factors close to unity with uncertainties ranging from 2% to 12% depending on the jet transverse momentum.

Observation of ttH Production

The observation of Higgs boson production in association with a top quark-antiquark pair is reported, based on a combined analysis of proton-proton collision data at center-of-mass energies of √s = 7, 8, and 13 TeV, corresponding to integrated luminosities of up to 5.1, 19.7, and 35.9 fb^(-1), respectively. The data were collected with the CMS detector at the CERN LHC. The results of statistically independent searches for Higgs bosons produced in conjunction with a top quark-antiquark pair and decaying to pairs of W bosons, Z bosons, photons, τ leptons, or bottom quark jets are combined to maximize sensitivity. An excess of events is observed, with a significance of 5.2 standard deviations, over the expectation from the background-only hypothesis. The corresponding expected significance from the standard model for a Higgs boson mass of 125.09 GeV is 4.2 standard deviations. The combined best fit signal strength normalized to the standard model prediction is 1.26^(+0.31)_(−0.26).

Observation of tt[over ¯]H Production.

The observation of Higgs boson production in association with a top quark-antiquark pair is reported, based on a combined analysis of proton-proton collision data at center-of-mass energies of sqrt[s]=7, 8, and 13TeV, corresponding to integrated luminosities of up to 5.1, 19.7, and 35.9 fb^{-1}, respectively. The data were collected with the CMS detector at the CERN LHC. The results of statistically independent searches for Higgs bosons produced in conjunction with a top quark-antiquark pair and decaying to pairs of W bosons, Z bosons, photons, τ leptons, or bottom quark jets are combined to maximize sensitivity. An excess of events is observed, with a significance of 5.2 standard deviations, over the expectation from the background-only hypothesis. The corresponding expected significance from the standard model for a Higgs boson mass of 125.09GeV is 4.2 standard deviations. The combined best fit signal strength normalized to the standard model prediction is 1.26_{-0.26}^{+0.31}.

Search for supersymmetry in events with one lepton and multiple jets exploiting the angular correlation between the lepton and the missing transverse momentum in proton–proton collisions at [formula omitted

Results are presented from a search for supersymmetry in events with a single electron or muon and hadronic jets. The data correspond to a sample of proton–proton collisions at s=13TeV with an integrated luminosity of 35.9fb−1, recorded in 2016 by the CMS experiment. A number of exclusive search regions are defined according to the number of jets, the number of b -tagged jets, the scalar sum of the transverse momenta of the jets, and the scalar sum of the missing transverse momentum and the transverse momentum of the lepton. Standard model background events are reduced significantly by requiring a large azimuthal angle between the direction of the lepton and of the reconstructed W boson, computed under the hypothesis that all of the missing transverse momentum in the event arises from a neutrino produced in the leptonic decay of the W boson. The numbers of observed events are consistent with the expectations from standard model processes, and the results are used to set lower limits on supersymmetric particle masses in the context of two simplified models of gluino pair production. In the first model, where each gluino decays to a top quark–antiquark pair and a neutralino, gluino masses up to 1.8 TeV are excluded at the 95% CL. The second model considers a three-body decay to a light quark–antiquark pair and a chargino, which subsequently decays to a W boson and a neutralino. In this model, gluinos are excluded up to 1.9 TeV.

Search for supersymmetry in events with at least three electrons or muons, jets, and missing transverse momentum in proton-proton collisions at sqrt{s}=13 TeV

A search for new physics is carried out in events with at least three electrons or muons in any combination, jets, and missing transverse momentum. Results are based on the sample of proton-proton collision data produced by the LHC at a center-of-mass energy of 13 TeV and collected by the CMS experiment in 2016. The data sample analyzed corresponds to an integrated luminosity of 35.9 fb−1. Events are classified according to the number of b jets, missing transverse momentum, hadronic transverse momentum, and the invariant mass of same-flavor dilepton pairs with opposite charge. No significant excess above the expected standard model background is observed. Exclusion limits at 95% confidence level are computed for four different supersymmetric simplified models with pair production of gluinos or third-generation squarks. In the model with gluino pair production, with subsequent decays into a top quark-antiquark pair and a neutralino, gluinos with masses smaller than 1610 GeV are excluded for a massless lightest supersymmetric particle. In the case of bottom squark pair production, the bottom squark masses are excluded up to 840 GeV for charginos lighter than 200 GeV. For a simplified model of heavy top squark pair production, the {tilde{mathrm{t}}}_2 mass is excluded up to 720, 780, or 710 GeV for models with an exclusive {tilde{mathrm{t}}}_2to {tilde{mathrm{t}}}_1mathrm{H} decay, an exclusive {tilde{mathrm{t}}}_2to {tilde{mathrm{t}}}_1mathrm{Z} decay, or an equally probable mix of those two decays. In order to provide a simplified version of the analysis for easier interpretation, a small set of aggregate signal regions also has been defined, providing a compromise between simplicity and analysis sensitivity.