Top Quark Production Research Articles

Exploring SMEFT operators in the tHq production at the LHC

We study the top-quark production along with a Higgs boson and a jet (tHq) at the LHC experiment within the framework of the Standard Model Effective Field Theory (SMEFT). A strategy is developed to constrain the Wilson Coefficients (WC) corresponding to the associated SMEFT operators using the latest LHC measurements. The best-fit values of these WCs are presented. Finally, we demonstrate the feasibility of finding the effects of these operators on various kinematical observables of the tHq process at the LHC. We find that for a set of best-fitted values of the considered WCs, the excess of signal over the backgrounds can be achieved with a reasonable significance at the center of mass energy s\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\sqrt{s} $$\\end{document} = 13 TeV and for integrated luminosity options L\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\mathcal{L} $$\\end{document} =300 fb−1 and 3000 fb−1.

Single-Top Quark Physics at the LHC: From Precision Measurements to Rare Processes and Top Quark Properties

Since the initial measurements of single-top quark production at the Tevatron in 2009, tremendous progress has been made at the LHC. While LHC Run 1 marked the beginning of a precision era for the single-top quark measurements in some of the main production mechanisms, LHC Run 2 witnessed the emergence and exploration of new processes associating top quark production with a neutral boson. In this paper, we review the measurements of the three main production mechanisms (t-channel, s-channel, and tW production), and of the associated production with a photon, a Z boson, or a Higgs boson. Differential cross-sections are measured for several of these processes and compared with theoretical predictions. The top quark properties that can be measured in single-top quark processes are scrutinized, such as Wtb couplings and top quark couplings with neutral bosons, and the polarizations of both the W boson and top quark. The effective field theory framework is emerging as a standard for interpreting property measurements. Perspectives for LHC Run 3 and the HL-LHC are discussed in the conclusions.

Top quark and vector meson production in heavy ion collisions at CMS

Heavy ion collisions are rich and complex systems that involve different aspects of QCD and electromagnetic phenomena. From head-on collisions to the case in which the nuclei miss each other, many of QCD and photo-induced probes are being actively investigated. In this contribution we briefly discuss both of these different topics and some of the CMS results on top quark production and vector meson photo-production, as well as the physics motivation to study these processes are presented.

Constraining the top-quark mass within the global MSHT PDF fit

We examine the ability of experimental measurements of top-quark pair production to constrain both the top-quark mass and the strong coupling within the global MSHT parton distribution function (PDF) fit. Specifically, we consider ATLAS and CMS measurements of differential distributions taken at a centre-of-mass energy of 8 TeV, as well as tbar{t} total cross section data taken at a variety of experiments, and compare to theoretical predictions including next-to-next-to-leading order corrections. We find that supplementing the global fit with this additional information results in relatively strong constraints on the top-quark mass, and is also able to bound the strong coupling in a limited fashion. Our final result is m_t=173.0pm 0.6~textrm{GeV} and is compatible with the world average pole mass extracted from cross section measurements of 172.5pm 0.7~textrm{GeV} by the Particle Data Group. We also study the effect of different top-quark masses on the gluon parton distribution function, finding changes at high x which nonetheless lie within the large PDF uncertainties in this region.

Application of deep learning in top pair and single top quark production at the LHC

Application of deep learning in top pair and single top quark production at the LHC

The potential of a TeV-scale muon-ion collider

We propose the development of a novel muon-proton and muon-nucleus collider facility at the TeV scale that is capable of performing precision deep inelastic scattering measurements in new regimes and providing a rich program in nuclear and particle physics. Such a facility could seed, or leverage, the development of a muon-antimuon collider and make use of the existing hadron accelerator infrastructure when sited at a facility such as Brookhaven National Laboratory, Fermilab, or CERN. We discuss the possible energy and luminosity design parameters for several collider configurations, and illustrate the science potential with several studies on deep inelastic scattering kinematics, Higgs and vector boson production, top quark production, and beyond Standard Model leptoquark production. Detector design considerations and a possible road map toward development are also given.

Search for a light charged Higgs boson in t → H±b decays, with H± → cb, in the lepton+jets final state in proton-proton collisions at s\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\sqrt{s} $$\\end{document} = 13 TeV with the ATLAS detector

A search for a charged Higgs boson, H±, produced in top-quark decays, t → H±b, is presented. The search targets H± decays into a bottom and a charm quark, H± → cb. The analysis focuses on a selection enriched in top-quark pair production, where one top quark decays into a leptonically decaying W boson and a bottom quark, and the other top quark decays into a charged Higgs boson and a bottom quark. This topology leads to a lepton-plus-jets final state, characterised by an isolated electron or muon and at least four jets. The search exploits the high multiplicity of jets containing b-hadrons, and deploys a neural network classifier that uses the kinematic differences between the signal and the background. The search uses a dataset of proton-proton collisions collected at a centre-of-mass energy s\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\sqrt{s} $$\\end{document} = 13 TeV between 2015 and 2018 with the ATLAS detector at CERN’s Large Hadron Collider, amounting to an integrated luminosity of 139 fb−1. Observed (expected) 95% confidence-level upper limits between 0.15% (0.09%) and 0.42% (0.25%) are derived for the product of branching fractions B\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\mathcal{B} $$\\end{document}(t → H±b) × B(H± → cb) for charged Higgs boson masses between 60 and 160 GeV, assuming the SM production of the top-quark pairs.

Associated production of a top-quark pair with two isolated photons at the LHC through NLO in QCD

We report on the computation of NLO QCD corrections to top-quark pair production in association with two photons at the LHC. Higher-order effects and photon bremsstrahlung are taken into account in the production and decays of the top-quark pair. Top-quark and W-boson decays are treated in the Narrow Width Approximation conserving spin correlations up to NLO in QCD. This is the first time that the complete set of NLO QCD corrections to the ppto toverline{t}gamma gamma process including top-quark decays is calculated. We present results at the integrated and differential cross-section level in the di-lepton and lepton + jet channel. In addition, we investigate the effect of photon bremsstrahlung in toverline{t} production and top-quark decays, as well as the mixed contribution. The latter contribution, in which two photons occur simultaneously in the production and decay of the toverline{t} pair, proved to be significant at both the integrated and differential cross-section level.

Combination of inclusive top-quark pair production cross-section measurements using ATLAS and CMS data at sqrt{s} = 7 and 8 TeV

A combination of measurements of the inclusive top-quark pair production cross-section performed by ATLAS and CMS in proton–proton collisions at centre-of-mass energies of 7 and 8 TeV at the LHC is presented. The cross-sections are obtained using top-quark pair decays with an opposite-charge electron–muon pair in the final state and with data corresponding to an integrated luminosity of about 5 fb−1 at sqrt{s} = 7 TeV and about 20 fb−1 at sqrt{s} = 8 TeV for each experiment. The combined cross-sections are determined to be 178.5 ± 4.7 pb at sqrt{s} = 7 TeV and {243.3}_{-5.9}^{+6.0} pb at sqrt{s} = 8 TeV with a correlation of 0.41, using a reference top-quark mass value of 172.5 GeV. The ratio of the combined cross-sections is determined to be R8/7 = 1.363 ± 0.032. The combined measured cross-sections and their ratio agree well with theory calculations using several parton distribution function (PDF) sets. The values of the top-quark pole mass (with the strong coupling fixed at 0.118) and the strong coupling (with the top-quark pole mass fixed at 172.5 GeV) are extracted from the combined results by fitting a next-to-next-to-leading-order plus next-to-next-to-leading-log QCD prediction to the measurements. Using a version of the NNPDF3.1 PDF set containing no top-quark measurements, the results obtained are {m}_t^{textrm{pole}}={173.4}_{-2.0}^{+1.8} GeV and {alpha}_{textrm{s}}left({m}_Zright)={0.1170}_{-0.0018}^{+0.0021} .

Search for a new scalar resonance in flavour-changing neutral-current top-quark decays t → qX (q = u, c), with X → boverline{b} , in proton-proton collisions at sqrt{s} = 13 TeV with the ATLAS detector

A search for flavour-changing neutral-current decays of a top quark into an up-type quark (either up or charm) and a light scalar particle X decaying into a bottom anti-bottom quark pair is presented. The search focuses on top-quark pair production where one top quark decays to qX, with X → boverline{b} , and the other top quark decays according to the Standard Model, with the W boson decaying leptonically. The final state is thus characterised by an isolated electron or muon and at least four jets. Events are categorised according to the multiplicity of jets and jets tagged as originating from b-quarks, and a neural network is used to discriminate between signal and background processes. The data analysed correspond to 139 fb−1 of proton–proton collisions at a centre-of-mass energy of 13 TeV, recorded with the ATLAS detector at the LHC. The 95% confidence-level upper limits between 0.019% and 0.062% are derived for the branching fraction mathcal{B} (t → uX) and between 0.018% and 0.078% for the branching fraction mathcal{B} (t → cX), for masses of the scalar particle X between 20 and 160 GeV.

Inclusive and differential cross-sections for dilepton toverline{t} production measured in sqrt{s} = 13 TeV pp collisions with the ATLAS detector

Differential and double-differential distributions of kinematic variables of leptons from decays of top-quark pairs ( toverline{t} ) are measured using the full LHC Run 2 data sample collected with the ATLAS detector. The data were collected at a pp collision energy of sqrt{s} = 13 TeV and correspond to an integrated luminosity of 140 fb−1. The measurements use events containing an oppositely charged eμ pair and b-tagged jets. The results are compared with predictions from several Monte Carlo generators. While no prediction is found to be consistent with all distributions, a better agreement with measurements of the lepton pT distributions is obtained by reweighting the toverline{t} sample so as to reproduce the top-quark pT distribution from an NNLO calculation. The inclusive top-quark pair production cross-section is measured as well, both in a fiducial region and in the full phase-space. The total inclusive cross-section is found to beσtt¯=829±1stat±13syst±8lumi±2beampb,\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {\\sigma}_{t\\overline{t}}=829\\pm 1\\ \\left(\ extrm{stat}\\right)\\pm 13\\ \\left(\ extrm{syst}\\right)\\pm 8\\ \\left(\ extrm{lumi}\\right)\\pm 2\\ \\left(\ extrm{beam}\\right)\\ \ extrm{pb}, $$\\end{document}where the uncertainties are due to statistics, systematic effects, the integrated luminosity and the beam energy. This is in excellent agreement with the theoretical expectation.

Measurement of inclusive and differential cross sections for single top quark production in association with a W boson in proton-proton collisions at sqrt{s} = 13 TeV

Measurements of the inclusive and normalised differential cross sections are presented for the production of single top quarks in association with a W boson in proton-proton collisions at a centre-of-mass energy of 13 TeV. The data used were recorded with the CMS detector at the LHC during 2016–2018, and correspond to an integrated luminosity of 138 fb−1. Events containing one electron and one muon in the final state are analysed. For the inclusive measurement, a multivariate discriminant, exploiting the kinematic properties of the events is used to separate the signal from the dominant textrm{t}overline{textrm{t}} background. A cross section of 79.2pm 0.9{left(textrm{stat}right)}_{-8.0}^{+7.7}left(textrm{syst}right)pm 1.2left(textrm{lumi}right) pb is obtained, consistent with the predictions of the standard model. For the differential measurements, a fiducial region is defined according to the detector acceptance, and the requirement of exactly one jet coming from the fragmentation of a bottom quark. The resulting distributions are unfolded to particle level and agree with the predictions at next-to-leading order in perturbative quantum chromodynamics.

Search for CP violating top quark couplings in pp collisions at sqrt{s} = 13 TeV

Results are presented from a search for CP violation in top quark pair production, using proton-proton collisions at a center-of-mass energy of 13 TeV. The data used for this analysis consist of final states with two charged leptons collected by the CMS experiment, and correspond to an integrated luminosity of 35.9 fb−1. The search uses two observables, mathcal{O} 1 and mathcal{O} 3, which are Lorentz scalars. The observable mathcal{O} 1 is constructed from the four-momenta of the charged leptons and the reconstructed top quarks, while mathcal{O} 3 consists of the four-momenta of the charged leptons and the b quarks originating from the top quarks. Asymmetries in these observables are sensitive to CP violation, and their measurement is used to determine the chromoelectric dipole moment of the top quark. The results are consistent with the expectation from the standard model.

Measurement of the differential hbox {t}overline{hbox {t}} production cross section as a function of the jet mass and extraction of the top quark mass in hadronic decays of boosted top quarks

A measurement of the jet mass distribution in hadronic decays of Lorentz-boosted top quarks is presented. The measurement is performed in the lepton + jets channel of top quark pair production (hbox {t}overline{hbox {t}}) events, where the lepton is an electron or muon. The products of the hadronic top quark decay are reconstructed using a single large-radius jet with transverse momentum greater than 400,text {Ge}hspace{-.08em}text {V}. The data were collected with the CMS detector at the LHC in proton-proton collisions and correspond to an integrated luminosity of 138,text {fb}^{-1}. The differential hbox {t}overline{hbox {t}} production cross section as a function of the jet mass is unfolded to the particle level and is used to extract the top quark mass. The jet mass scale is calibrated using the hadronic W boson decay within the large-radius jet. The uncertainties in the modelling of the final state radiation are reduced by studying angular correlations in the jet substructure. These developments lead to a significant increase in precision, and a top quark mass of 173.06 pm 0.84,text {Ge}hspace{-.08em}text {V} .

Electroweak radiative corrections to polarized top quark pair production

Electroweak radiative corrections to polarized top quark pair production

Measurement of single top-quark production in the s-channel in proton–proton collisions at sqrt{s} = 13 TeV with the ATLAS detector

A measurement of single top-quark production in the s-channel is performed in proton–proton collisions at a centre-of-mass energy of 13 TeV with the ATLAS detector at the CERN Large Hadron Collider. The dataset corresponds to an integrated luminosity of 139 fb−1. The analysis is performed on events with an electron or muon, missing transverse momentum and exactly two b-tagged jets in the final state. A discriminant based on matrix element calculations is used to separate single-top-quark s-channel events from the main background contributions, which are top-quark pair production and W-boson production in association with jets. The observed (expected) signal significance over the background-only hypothesis is 3.3 (3.9) standard deviations, and the measured cross-section is sigma ={8.2}_{-2.9}^{+3.5} pb, consistent with the Standard Model prediction of {sigma}^{textrm{SM}}={10.32}_{-0.36}^{+0.40} pb.

Search for flavour-changing neutral current interactions of the top quark and the Higgs boson in events with a pair of τ-leptons in pp collisions at sqrt{s} = 13 TeV with the ATLAS detector

A search for flavour-changing neutral current (FCNC) tqH interactions involving a top quark, another up-type quark (q = u, c), and a Standard Model (SM) Higgs boson decaying into a τ-lepton pair (H → τ+τ−) is presented. The search is based on a dataset of pp collisions at sqrt{s} = 13 TeV that corresponds to an integrated luminosity of 139 fb−1 recorded with the ATLAS detector at the Large Hadron Collider. Two processes are considered: single top quark FCNC production in association with a Higgs boson (pp → tH), and top quark pair production in which one of top quarks decays into Wb and the other decays into qH through the FCNC interactions. The search selects events with two hadronically decaying τ-lepton candidates (τhad) or at least one τhad with an additional lepton (e, μ), as well as multiple jets. Event kinematics is used to separate signal from the background through a multivariate discriminant. A slight excess of data is observed with a significance of 2.3σ above the expected SM background, and 95% CL upper limits on the t → qH branching ratios are derived. The observed (expected) 95% CL upper limits set on the t → cH and t → uH branching ratios are 9.4times {10}^{-4}left({4.8}_{-1.4}^{+2.2}times {10}^{-4}right) and 6.9times {10}^{-4}left({3.5}_{-1.0}^{+1.5}times {10}^{-4}right) , respectively. The corresponding combined observed (expected) upper limits on the dimension-6 operator Wilson coefficients in the effective tqH couplings are Ccϕ< 1.35 (0.97) and Cuϕ< 1.16 (0.82).

Study of additional jet activity in top quark pair production and decay at the LHC

We report on the calculation of the NLO QCD corrections to top quark pair production in association with two hard jets at the LHC. We take into account higher-order effects in both the production and decays of the top-quark pair. The latter are treated in the narrow width approximation and $t\bar{t}$ spin correlations are preserved throughout the calculation. This is the first time that such a complete study for this process is conducted at NLO in QCD. We present results for fiducial cross sections at the integrated and differential level. Furthermore, we investigate kinematic properties of the additional light jets and their distribution in the $pp\to t\bar{t}jj$ process. We examine jets in production and top-quark decays as well as the mixed contribution, where the two hardest non-$b$ jets are present simultaneously in the production and decay processes.

Measurement of the charge asymmetry in top-quark pair production in association with a photon with the ATLAS experiment

A measurement of the charge asymmetry in top-quark pair (tt¯) production in association with a photon is presented. The measurement is performed in the single-lepton tt¯ decay channel using proton–proton collision data collected with the ATLAS detector at the Large Hadron Collider at CERN at a centre-of-mass-energy of 13 TeV during the years 2015–2018, corresponding to an integrated luminosity of 139 fb−1. The charge asymmetry is obtained from the distribution of the difference of the absolute rapidities of the top quark and antiquark using a profile likelihood unfolding approach. It is measured to be AC=−0.003±0.029 in agreement with the Standard Model expectation.

Energy-peak based method to measure top quark mass via B-hadron decay lengths

We develop a method for the determination of the top quark mass using the distribution of the decay length of the B-hadrons originating from its decay. This technique is based on our earlier observation regarding the location of the peak of the b quark energy distribution. Such “energy-peak” methods enjoy a greater degree of model-independence with respect to the kinematics of top quark production compared to earlier proposals. The CMS experiment has implemented the energy-peak method using associated b-jet energy as an approximation for b quark energy. The new method uses B-hadron decay lengths, which are related to b quark energies by convolution. The advantage of the new decay length method is that it can be applied in a way that evades jet-energy scale (JES) uncertainties. Indeed, CMS has measured the top quark mass using B-hadron decay lengths, but they did not incorporate the energy-peak method. Therefore, mismodeling of top quark transverse momentum remains a large uncertainty in their result. We demonstrate that, using energy-peak methods, this systematic uncertainty can become negligible. We show that with the current LHC data set, a sub-GeV statistical uncertainty on the top quark mass can be attained with this method. To achieve a comparable systematic uncertainty as is true for many methods based on exclusive or semi-inclusive observables using hadrons, we find that the quark-hadron transition needs to be described significantly better than is the case with current fragmentation functions and hadronization models.