Top-quark Transverse Momentum Research Articles

SMEFT chromomagnetic dipole operator contributions to tt¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$t{{\\bar{t}}}$$\\end{document} production at approximate NNLO in QCD

We study higher-order QCD corrections for the production of a top–antitop quark pair (tt¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$t{{\\bar{t}}}$$\\end{document} production) at the Large Hadron Collider in the Standard Model Effective Field Theory. We consider effects of new physics parametrized by the top-quark chromomagnetic dipole operator. We calculate new physics contributions to the total cross section at approximate NNLO, with second-order soft-gluon corrections added to the complete NLO result, including uncertainties from scale dependence and from parton distributions. We also calculate new physics contributions at approximate NNLO for differential distributions in top-quark transverse momentum.

Soft-gluon corrections in [formula omitted] production

We study higher-order QCD corrections for the associated production of a top-antitop quark pair and a W boson (tt¯W production) in proton-proton collisions. We calculate approximate NNLO (aNNLO) and approximate N3LO (aN3LO) cross sections, with second-order and third-order soft-gluon corrections added to the exact NLO QCD result, and we also include electroweak (EW) corrections through NLO. We calculate uncertainties from scale dependence, which are reduced at higher orders, and from parton distributions, and we also provide separate results for tt¯W+ and tt¯W− production. We compare our results to recent measurements from the LHC, and we find that the aN3LO QCD + NLO EW predictions provide improved agreement with the data. We also calculate differential distributions in top-quark transverse momentum and rapidity and find significant enhancements from the higher-order corrections. This is the first calculation of soft-gluon corrections in single-particle-inclusive kinematics for a 2→3 process where all final-state particles are massive.

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.

Higher-order corrections in tt¯γ cross sections

We study higher-order QCD corrections for the associated production of a top-antitop quark pair and a photon ($t\overline{t}\ensuremath{\gamma}$ production) in proton-proton collisions. We calculate the approximate next-to-next-to-leading order cross section, with second-order soft-gluon corrections added to the complete next-to-leading order result, including uncertainties from scale dependence and from parton distributions. We compare our results to recent measurements from the LHC, and find that the soft-gluon corrections provide improved agreement with the data. We also calculate differential distributions in top-quark transverse momentum and rapidity.

Projected transverse momentum resummation in top-antitop pair production at LHC

The transverse momentum distribution of the toverline{t} system is of both experimental and theoretical interest. In the presence of azimuthally asymmetric divergences, pursuing resummation at high logarithmic precision is rather demanding in general. In this paper, we propose the projected transverse momentum spectrum textrm{d}{sigma}_{toverline{t}}/textrm{d}{q}_{tau } , which is derived from the classical {overrightarrow{q}}_{textrm{T}} spectrum by integrating out the rejection component {q}_{tau_{perp }} with respect to a reference unit vector overrightarrow{tau} , to serve as an alternative solution to remove these asymmetric divergences, in addition to the azimuthally averaged case textrm{d}{sigma}_{toverline{t}}/textrm{d}mid {overrightarrow{q}}_{textrm{T}}mid . In the context of the effective field theories, SCETII and HQET, we will demonstrate that in spite of the {q}_{tau_{perp }} integrations, the leading asymptotic terms of textrm{d}{sigma}_{toverline{t}}/textrm{d}{q}_{tau } still observe the factorisation pattern in terms of the hard, beam, and soft functions in the vicinity of qτ = 0 GeV. Then, with the help of the renormalisation group equation techniques, we carry out the resummation at NLL+NLO, N2LL+N2LO, and approximate N2LL′+N2LO accuracy on three observables of interest, textrm{d}{sigma}_{toverline{t}}/d{q}_{textrm{T},textrm{in}},textrm{d}{sigma}_{toverline{t}}/textrm{d}{q}_{textrm{T},textrm{out}} , and textrm{d}{sigma}_{toverline{t}}/dDelta {phi}_{toverline{t}} , within the domain {M}_{toverline{t}} ≥ 400 GeV. The first two cases are obtained by choosing overrightarrow{tau} parallel and perpendicular to the top quark transverse momentum, respectively. The azimuthal de-correlation Delta {phi}_{toverline{t}} of the toverline{t} pair is evaluated through its kinematical connection to qT,out. This is the first time the azimuthal spectrum Delta {phi}_{toverline{t}} is appraised at or beyond the N2LL level including a consistent treatment of both beam collinear and soft radiation.

QCD corrections in tqgamma production at hadron colliders

We study QCD corrections for the associated production of a single top quark and a photon (tqgamma production) at hadron colliders. We calculate the NLO cross section at LHC and future collider energies for a variety of kinematical cuts, and we estimate uncertainties from scale dependence and from parton distributions. We also calculate differential distributions in top-quark transverse-momentum and rapidity as well as photon energy. Finally, we study higher-order corrections from soft-gluon emission for this process, and we provide approximate NNLO (aNNLO) results for the cross section and top-quark differential distributions. We also compare our calculations with recent measurements from CMS and ATLAS at the LHC and find that the aNNLO corrections improve the comparison between the data and the Standard Model predictions.

$tW$ and $tZ'$ production at hadron colliders

We present theoretical results with soft-gluon corrections for two separate processes: (1) the production of a single top quark in association with a W boson in the Standard Model; and (2) the production of a single top quark in association with a heavy Z' boson in new physics models with or without anomalous couplings. We show that the higher-order corrections from soft-gluon emission are dominant for a wide range of collider energies. Results are shown for the total cross sections and top-quark transverse-momentum and rapidity distributions for tW and tZ' production at LHC and future collider energies up to 100 TeV. The uncertainties from scale dependence and parton distribution functions are also analyzed.

Resummation for $tqH$ production

We present results with soft-gluon resummation for the associated production of a single top quark and a Higgs boson. We present analytical results for the higher-order soft-gluon corrections and numerical results for the total cross section and top-quark transverse momentum and rapidity distributions at LHC energies.

Measurements of differential cross-sections in top-quark pair events with a high transverse momentum top quark and limits on beyond the Standard Model contributions to top-quark pair production with the ATLAS detector at sqrt{s} = 13 TeV

Cross-section measurements of top-quark pair production where the hadronically decaying top quark has transverse momentum greater than 355 GeV and the other top quark decays into ℓνb are presented using 139 fb−1 of data collected by the ATLAS experiment during proton-proton collisions at the LHC. The fiducial cross-section at sqrt{s} = 13 TeV is measured to be σ = 1.267 ± 0.005 ± 0.053 pb, where the uncertainties reflect the limited number of data events and the systematic uncertainties, giving a total uncertainty of 4.2%. The cross-section is measured differentially as a function of variables characterising the toverline{t} system and additional radiation in the events. The results are compared with various Monte Carlo generators, including comparisons where the generators are reweighted to match a parton-level calculation at next-to-next-to-leading order. The reweighting improves the agreement between data and theory. The measured distribution of the top-quark transverse momentum is used to search for new physics in the context of the effective field theory framework. No significant deviation from the Standard Model is observed and limits are set on the Wilson coefficients of the dimension-six operators OtG and {O}_{tq}^{(8)} , where the limits on the latter are the most stringent to date.

Soft-gluon corrections for the associated production of a single top quark and a Higgs boson

We discuss soft-gluon resummation for the associated production of a single top quark and a Higgs boson ($tqH$ production) in single-particle-inclusive (1PI) kinematics. We present analytical results for the higher-order corrections and numerical results for the cross sections at LHC energies. We calculate approximate NNLO total rates, including scale dependence and uncertainties from parton distributions, as well as top-quark transverse-momentum and rapidity distributions. In all cases we find that the soft-gluon corrections are dominant and provide important contributions to the total and differential cross sections.

Measurements of top-quark pair single- and double-differential cross-sections in the all-hadronic channel in pp collisions at sqrt{mathrm{s}} = 13 TeV using the ATLAS detector

Differential cross-sections are measured for top-quark pair production in the all-hadronic decay mode, using proton-proton collision events collected by the ATLAS experiment in which all six decay jets are separately resolved. Absolute and normalised single- and double-differential cross-sections are measured at particle and parton level as a function of various kinematic variables. Emphasis is placed on well-measured observables in fully reconstructed final states, as well as on the study of correlations between the top-quark pair system and additional jet radiation identified in the event. The study is performed using data from proton-proton collisions at sqrt{s} = 13 TeV collected by the ATLAS detector at CERN’s Large Hadron Collider in 2015 and 2016, corresponding to an integrated luminosity of 36.1 fb−1. The rapidities of the individual top quarks and of the top-quark pair are well modelled by several independent event generators. Significant mismodelling is observed in the transverse momenta of the leading three jet emissions, while the leading top-quark transverse momentum and top-quark pair transverse momentum are both found to be incompatible with several theoretical predictions.

Measurement of differential cross sections and charge ratios for t-channel single top quark production in proton\u2013proton collisions at sqrt{s}=13,text {Te}text {V}

A measurement is presented of differential cross sections for t-channel single top quark and antiquark production in proton–proton collisions at a centre-of-mass energy of 13,text {Te}text {V} by the CMS experiment at the LHC. From a data set corresponding to an integrated luminosity of 35.9,text {fb}^{-1}, events containing one muon or electron and two or three jets are analysed. The cross section is measured as a function of the top quark transverse momentum (p_{mathrm{T}} ), rapidity, and polarisation angle, the charged lepton p_{mathrm{T}} and rapidity, and the p_{mathrm{T}} of the text {W}{}{} boson from the top quark decay. In addition, the charge ratio is measured differentially as a function of the top quark, charged lepton, and text {W}{}{} boson kinematic observables. The results are found to be in agreement with standard model predictions using various next-to-leading-order event generators and sets of parton distribution functions. Additionally, the spin asymmetry, sensitive to the top quark polarisation, is determined from the differential distribution of the polarisation angle at parton level to be 0.440 pm 0.070, in agreement with the standard model prediction.

Associated production of a top quark with a photon via anomalous couplings

We discuss the associated production of a top quark with a photon via anomalous $t$-$q$-$\gamma$ couplings, and present higher-order corrections from soft-gluon emission for the processes $gq \rightarrow t\gamma$ at LHC energies. We perform soft-gluon resummation at next-to-leading-logarithm accuracy and derive approximate next-to-next-to-leading order (aNNLO) double-differential cross sections. We calculate at aNNLO the total $t\gamma$ production cross sections and the top-quark transverse-momentum and rapidity distributions for various LHC energies, and show that the soft-gluon corrections are large and dominant in these processes.

Measurements of differential cross sections of top quark pair production in association with jets in pp collisions at sqrt{s}=13 TeV using the ATLAS detector

Measurements of differential cross sections of top quark pair production in association with jets by the ATLAS experiment at the LHC are presented. The measurements are performed as functions of the top quark transverse momentum, the transverse momentum of the top quark-antitop quark system and the out-of-plane transverse momentum using data from pp collisions at sqrt{s}=13 TeV collected by the ATLAS detector at the LHC in 2015 and corresponding to an integrated luminosity of 3.2 fb−1. The top quark pair events are selected in the lepton (electron or muon) + jets channel. The measured cross sections, which are compared to several predictions, allow a detailed study of top quark production.

Higher-order corrections for tZ production via anomalous couplings

I present higher-order corrections from soft-gluon emission for the associated production of a top quark with a $Z$ boson via anomalous $t\text{\ensuremath{-}}q\text{\ensuremath{-}}Z$ couplings at LHC energies. Approximate next-to-next-to-leading order (aNNLO) double-differential cross sections are derived from soft-gluon resummation at next-to-leading-logarithm accuracy. The total $tZ$ production cross sections and the top-quark transverse-momentum and rapidity distributions are calculated at aNNLO for various LHC energies. It is shown that the soft-gluon corrections are dominant and large for this process.

Single-top and top-antitop cross sections

I present high-order calculations, including soft-gluon corrections, for single-top and top-antitop production cross sections and differential distributions. For single-top production, results are presented for the three different channels in the Standard Model, for associated production with a charged Higgs, and for processes involving anomalous couplings. For top-antitop pair production, total cross sections and top-quark transverse-momentum and rapidity distributions are presented for various LHC energies.

Soft-gluon corrections for tW production at N3LO

I present approximate results that include third-order soft-gluon corrections for the associated production of a single top quark with a $W$ boson. The calculation uses expressions from soft-gluon resummation at next-to-next-to-leading-logarithm (NNLL) accuracy. From the NNLL resummed cross section I derive approximate next-to-next-to-next-to-leading order (aN$^3$LO) cross sections for the process $bg \rightarrow tW^-$ at LHC and Tevatron energies. The aN$^3$LO top-quark transverse-momentum and rapidity distributions in $tW$ production are also presented.

Measurements of top-quark pair differential cross-sections in the lepton+jets channel in pp collisions at [Formula: see text] using the ATLAS detector.

Measurements of normalized differential cross-sections of top-quark pair production are presented as a function of the top-quark, tbar{t} system and event-level kinematic observables in proton–proton collisions at a centre-of-mass energy of sqrt{s}=8,mathrm{TeV}. The observables have been chosen to emphasize the tbar{t} production process and to be sensitive to effects of initial- and final-state radiation, to the different parton distribution functions, and to non-resonant processes and higher-order corrections. The dataset corresponds to an integrated luminosity of 20.3 fb^{-1}, recorded in 2012 with the ATLAS detector at the CERN Large Hadron Collider. Events are selected in the lepton+jets channel, requiring exactly one charged lepton and at least four jets with at least two of the jets tagged as originating from a b-quark. The measured spectra are corrected for detector effects and are compared to several Monte Carlo simulations. The results are in fair agreement with the predictions over a wide kinematic range. Nevertheless, most generators predict a harder top-quark transverse momentum distribution at high values than what is observed in the data. Predictions beyond NLO accuracy improve the agreement with data at high top-quark transverse momenta. Using the current settings and parton distribution functions, the rapidity distributions are not well modelled by any generator under consideration. However, the level of agreement is improved when more recent sets of parton distribution functions are used.

Charged Higgs production in association with a top quark at approximate NNLO

I present approximate next-to-next-to-leading-order (aNNLO) total and differential cross sections for charged Higgs production in association with a top quark at LHC energies. The aNNLO results for the process $bg \rightarrow tH^-$ are derived from next-to-next-to-leading-logarithm (NNLL) resummation of soft-gluon corrections. Scale and parton-distribution uncertainties for the cross sections are shown. The top-quark transverse-momentum and rapidity distributions are also calculated.

Measurement of the differential cross-section of highly boosted top quarks as a function of their transverse momentum ins=8 TeVproton-proton collisions using the ATLAS detector

The differential cross-section for pair production of top quarks with high transverse momentum is measured in 20.3 fb$^{-1}$ of proton-proton collisions at a center-of-mass energy of 8 TeV. The measurement is performed for $t\bar{t}$ events in the lepton+jets channel. The cross-section is reported as a function of the hadronically decaying top quark transverse momentum for values above 300 GeV. The hadronically decaying top quark is reconstructed as an anti-$k_t$ jet with radius parameter $R=1.0$ and identified with jet substructure techniques. The observed yield is corrected for detector effects to obtain a cross-section at particle level in a fiducial region close to the event selection. A parton-level cross-section extrapolated to the full phase space is also reported for top quarks with transverse momentum above 300 GeV. The predictions of a majority of next-to-leading-order and leading-order matrix-element Monte Carlo generators are found to agree with the measured cross-sections.