Production Of Top Quark In Association Research Articles

Measurement of inclusive and differential cross sections of single top quark production in association with a W boson in proton-proton collisions at s = 13.6 TeV

The first measurement of the inclusive and normalised differential cross sections of single top quark production in association with a W boson in proton-proton collisions at a centre-of-mass energy of 13.6 TeV is presented. The data were recorded with the CMS detector at the LHC in 2022, and correspond to an integrated luminosity of 34.7 fb−1. The analysed events contain one muon and one electron in the final state. For the inclusive measurement, multivariate discriminants exploiting the kinematic properties of the events are used to separate the signal from the dominant top quark-antiquark production background. A cross section of 82.3±2.1stat−9.7+9.9syst±3.3lumi pb is obtained, consistent with the predictions of the standard model. A fiducial region is defined according to the detector acceptance to perform the differential measurements. The resulting differential distributions are unfolded to particle level and show good agreement with the predictions at next-to-leading order in perturbative quantum chromodynamics.

Probing effective operators in single top quark production in association with a lepton-neutrino pair

We study single top quark production in association with a lepton-neutrino pair at the LHC within the framework of the Standard Model effective field theory (SMEFT). We focus on relevant two-quark-two-lepton operators (Olq3, Olequ1, and Olequ3). It is known that these operators have tiny effects on the inclusive cross section of standard model tW production and are thus typically ignored in the SMEFT searches. However, we show that by employing smart observables, such as mT2, the pp→tℓν process is significantly sensitive to these operators. We set the most stringent limit on the coupling strength of the Olq3 operator by reinterpreting the results of a search for new phenomena with two opposite-charge leptons, jets and missing transverse momentum at s=13 TeV performed by the ATLAS collaboration. The limits derived on the Olequ1 and Olequ3 operators are comparable to those obtained from probing EFT effects in pp→tt¯ℓν and pp→tt¯ℓℓ processes at the LHC. Consequently, we propose to include the effects of these three operators on the pp→tℓν process in future global SMEFT analyses to increase the sensitivity and to reduce possible degeneracies. Published by the American Physical Society 2024

Angular correlations in associated top-quark and dark matter production at Large Hadron Collider

In this paper, we consider the processes of single top-quark production in association with dark matter particles through the t-channel in simplified models with scalar and pseudoscalar mediators. Within the framework of these models, we analyze the angular correlations that arise in the top quark production process in association with dark matter, comparing them with the production of a top quark in the Standard Model. We consider angular correlations of kinematic variables, which define admissible regions in momentum space and can be used experimentally to distinguish between the fraction of the total momentum carried away by the scalar or pseudoscalar mediator. We demonstrate that scalar mediator significantly changes the rest frame of the well-known angular correlation observable and changes the distributions. In this case, this variable provides clear separation between the SM and DM contribution and can be used to increase the sensitivity of future DM analyses.

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.

On soft gluon resummation for associated single top production with a Higgs boson at the LHC

We investigate threshold resummation of soft gluon corrections for the s-channel process of a single top quark production in association with a Higgs boson in the Standard Model. We choose to work in the three-particle invariant mass kinematics in direct QCD, i.e. in the space of Mellin moments. Our results take into account terms of up to next-to-leading logarithmic (NLL) precision, as well as {mathcal {O}} (alpha _{textrm{s}}) non-logarithmic terms which do not vanish at threshold. After presenting analytical expressions, we discuss the corresponding numerical results for the total cross section and the invariant mass distribution at the LHC.

Inclusive and differential cross section measurements of single top quark production in association with a Z boson in proton-proton collisions at sqrt{s} = 13 TeV

Inclusive and differential cross sections of single top quark production in association with a Z boson are measured in proton-proton collisions at a center-of-mass energy of 13 TeV with a data sample corresponding to an integrated luminosity of 138 fb−1 recorded by the CMS experiment. Events are selected based on the presence of three leptons, electrons or muons, associated with leptonic Z boson and top quark decays. The measurement yields an inclusive cross section of {87.9}_{-7.3}^{+7.5}{left(mathrm{stat}right)}_{-6.0}^{+7.3}left(mathrm{syst}right) fb for a dilepton invariant mass greater than 30 GeV, in agreement with standard model (SM) calculations and represents the most precise determination to date. The ratio between the cross sections for the top quark and the top antiquark production in association with a Z boson is measured as {2.37}_{-0.42}^{+0.56}{left(mathrm{stat}right)}_{-0.13}^{+0.27}left(mathrm{syst}right) . Differential measurements at parton and particle levels are performed for the first time. Several kinematic observables are considered to study the modeling of the process. Results are compared to theoretical predictions with different assumptions on the source of the initial-state b quark and found to be in agreement, within the uncertainties. Additionally, the spin asymmetry, which is sensitive to the top quark polarization, is determined from the differential distribution of the polarization angle at parton level to be 0.54 ± 0.16 (stat) ± 0.06 (syst), in agreement with SM predictions.

Single top production in association with a WZ pair at the LHC in the SMEFT

We study single top quark production in association with a WZ pair at the LHC in the context of the Standard Model (SM) and the Standard Model Effective Field Theory (SMEFT). A significant advantage of tWZ compared to other EW top production processes is its sensitivity to unitarity-violating behaviour induced in its 2 → 2 sub-amplitudes through modified EW interactions. At NLO in QCD, tWZ interferes with t overline{t} Z and t overline{t} and a method to meaningfully separate it from these overlapping processes needs to be employed. In order to define tWZ production for total rates and differential distributions, we consider the approaches proposed in the literature for similar cases and find that diagram-removal procedures provide reliable results both for the SM and the SMEFT in a suitably defined phase-space region. We provide robust results for total and differential cross sections for tWZ at 13 TeV, including the six relevant dimension-6 operators ( mathcal{O} tW, mathcal{O} tZ, mathcal{O} tG, {mathcal{O}}_{varphi Q}^{left(-right)} , {mathcal{O}}_{varphi Q}^{(3)} , mathcal{O} φt), also matching short-distance events to parton shower.

Probing FCNC couplings in single top-quark production associated with a neutral gauge boson in future lepton colliders

In this paper, we consider a single top-quark production in association with a neutral gauge boson (Z boson or photon) in the future electron–positron colliders. We utilize these channels to probe the top-quark flavor changing neutral current (FCNC) interactions in tqZ and tqγ vertices. We perform two separate analyses for top-Z-jet and top-γ-jet channels. The standard model effective field theory approach is employed to search for these anomalous couplings. We consider parton showering, hadronization and fast detector simulation in our study and use a cut-and-count technique to separate the signal from the standard model background processes. The upper limits on the FCNC couplings at 95% confidence level for different integrated luminosities are obtained. It is shown that the future lepton collider would be able to probe the FCNC branching fractions to Br(t → qγ) < 10−4 and Br(t → qZ) < 10−4 with 3 ab−1 of integrated luminosity of data at a center of mass energy of 350 GeV.

Measurement of single top-quark production in association with a W boson in the single-lepton channel at sqrt{s} = 8,text {TeV} with the ATLAS detector

The production cross-section of a top quark in association with a W boson is measured using proton–proton collisions at sqrt{s} = 8,text {TeV}. The dataset corresponds to an integrated luminosity of 20.2,text {fb}^{-1}, and was collected in 2012 by the ATLAS detector at the Large Hadron Collider at CERN. The analysis is performed in the single-lepton channel. Events are selected by requiring one isolated lepton (electron or muon) and at least three jets. A neural network is trained to separate the tW signal from the dominant t{bar{t}} background. The cross-section is extracted from a binned profile maximum-likelihood fit to a two-dimensional discriminant built from the neural-network output and the invariant mass of the hadronically decaying W boson. The measured cross-section is sigma _{tW} = 26 pm 7,text {pb}, in good agreement with the Standard Model expectation.

Observation of the associated production of a top quark and a Z boson in pp collisions at sqrt{s} = 13 TeV with the ATLAS detector

Single top-quark production in association with a Z boson, where the Z boson decays to a pair of charged leptons, is measured in the trilepton channel. The proton-proton collision data collected by the ATLAS experiment from 2015 to 2018 at a centre-of-mass energy of 13 TeV are used, corresponding to an integrated luminosity of 139 fb−1. Events containing three isolated charged leptons (electrons or muons) and two or three jets, one of which is identified as containing a b-hadron, are selected. The main backgrounds are from toverline{t}Z and diboson production. Neural networks are used to improve the background rejection and extract the signal. The measured cross-section for tℓ+ℓ−q production, including non-resonant dilepton pairs with {m}_{{mathrm{ell}}^{+}{mathrm{ell}}^{-}} > 30 GeV, is 97 ± 13 (stat.) ± 7 (syst.) fb, consistent with the Standard Model prediction.

Next-to-leading order QCD corrections for single top-quark production in association with two jets

In this article we calculate the next-to-leading order (NLO) QCD corrections for single on-shell top-quark production in association with two jets at proton-proton colliders. The tW channel is assumed to be measured independently. The QCD corrections to the inclusive cross section are about 28 (22)\% for top (anti-top) quark production at the 13 TeV LHC. Theoretical errors are dominated by scale uncertainties, which are found to be around 5\% at NLO. Results for various kinematical distributions are also provided using a well-motivated dynamical scale. The QCD corrections are found to have a non-trivial dependence on the phase-space.

Search for new physics in top quark production in dilepton final states in proton-proton collisions at sqrt{s} = 13,text {TeV}

A search for new physics in top quark production is performed in proton-proton collisions at 13,text {TeV} . The data set corresponds to an integrated luminosity of 35.9{,text {fb}^{-1}} collected in 2016 with the CMS detector. Events with two opposite-sign isolated leptons (electrons or muons), and mathrm{b} quark jets in the final state are selected. The search is sensitive to new physics in top quark pair production and in single top quark production in association with a mathrm{W} boson. No significant deviation from the standard model expectation is observed. Results are interpreted in the framework of effective field theory and constraints on the relevant effective couplings are set, one at a time, using a dedicated multivariate analysis. This analysis differs from previous searches for new physics in the top quark sector by explicitly separating mathrm{t}mathrm{W} from mathrm{t}{bar{mathrm{t}}} events and exploiting the specific sensitivity of the mathrm{t}mathrm{W} process to new physics.

Observation of Single Top Quark Production in Association with a Z Boson in Proton-Proton Collisions at sqrt[s]=13 TeV.

The observation of single top quark production in association with a Z boson and a quark (tZq) is reported. Events from proton-proton collisions at a center-of-mass energy of 13TeV containing three charged leptons (either electrons or muons) and at least two jets are analyzed. The data were collected with the CMS detector in 2016 and 2017 and correspond to an integrated luminosity of 77.4fb^{-1}. The increased integrated luminosity, a multivariate lepton identification, and a redesigned analysis strategy improve significantly the sensitivity of the analysis compared to previous searches for tZq production. The tZq signal is observed with a significance well over 5 standard deviations. The measured tZq production cross section is σ(pp→tZq→tℓ^{+}ℓ^{-}q)=111±13(stat)_{-9}^{+11}(syst) fb, for dilepton invariant masses above 30GeV, in agreement with the standard model expectation.

Soft-gluon corrections in top-quark production

I review calculations of soft-gluon corrections for top-quark production in hadron collisions. I describe theoretical formalisms for their resummation and for finite-order expansions. I show that soft-gluon corrections are dominant for a large number of top-quark processes. I discuss top–antitop pair production as well as single-top production, including total cross sections and differential distributions, and compare with data from the LHC and the Tevatron. I also discuss top-quark production in association with charged Higgs bosons, Z bosons and other particles in models of new physics.

Recent results on flavor physics by CMS

Differential production cross sections of the B+ meson and of J/ψ, ψ(2S), and ϒ(nS) (n=1,2,3) vector mesons are measured in pp collisions at 13 TeV, as a function of transverse momentum and rapidity, using data collected by the CMS detector in 2015. The B+ is reconstructed in the decay channel B+→J/ψK+ and the five S-wave quarkonium states are reconstructed in the dimuon decay channel.The simultaneous production of two ϒ(1S) mesons in observed at s=8 TeV in a data sample corresponding to an integrated luminosity of L=20.7 fb−1.The angular distributions and the differential branching fraction of the flavor changing neutral current decay B0→K⁎0μ+μ− are studied using data collected at s=8 TeV, as a function of the dimuon invariant mass squared.Flavor changing neutral currents in top quark couplings are searched through single top quark production in association with a photon, and in tt‾→Zq+Wb and tt‾→Hq+Wb decays, where Z→l+l− and H→γγ, WW, ZZ, τ+τ− and bb‾. The observed number of events agrees with the Standard Model prediction, and no evidence of flavor changing neutral currents is found.

Search for anomalous couplings via single top quark production in association with a photon at LHC

Considering the experimental constraints given by CMS collaboration at $\sqrt{s} = 8$ TeV on the strength of top quark flavour-changing neutral-current (FCNC) couplings $tq\gamma$ and $tqg$, we investigate the production of top quark in association with a photon and carry out a full simulation for the signals $\ell\nu b\gamma$ and $jjb\gamma$ at 14 TeV LHC. In our numerical analysis, the contributions of single top production with a photon radiation off the top decay products are also included. The discovery potential for anomalous couplings $tq\gamma$ and $tqg$ with an integrated luminosity of 100 fb$^{-1}$ are examined in detail.

Search for anomalous single top quark production in association with a photon in pp collisions at s = 8 $$ \sqrt{s}=8 $$ TeV

The result of a search for flavor changing neutral currents (FCNC) through single top quark production in association with a photon is presented. The study is based on proton-proton collisions at a center-of-mass energy of 8 TeV using data collected with the CMS detector at the LHC, corresponding to an integrated luminosity of 19.8 inverse femtobarns. The search for t gamma events where t to Wb and W to mu nu is conducted in final states with a muon, a photon, at least one hadronic jet with at most one being consistent with originating from a bottom quark, and missing transverse momentum. No evidence of single top quark production in association with a photon through a FCNC is observed. Upper limits at the 95% confidence level are set on the tu gamma and tc gamma anomalous couplings and translated into upper limits on the branching fraction of the FCNC top quark decays: B(t to u gamma) < 1.3E-4 and B(t to c gamma) < 1.7E-3. Upper limits are also set on the cross section of associated t gamma production in a restricted phase-space region. These are the most stringent limits currently available.

Top-quark and electroweak results from ATLAS and CMS

A selection of top-quark and electroweak results performed by ATLAS and CMS are presented. The results obtained with proton-proton collision at the center of mass energies of 7 and 8 TeV cover the 2010–2012 data taking period. We present the total and differential cross sections of the top-quark pair, single top-quark and top-quark production in association with a Gauge boson, together with some of the main properties of the top-quark as mass, charge asymmetry and spin. Regarding the electroweak physics, we present the total cross sections of single and double bosons and show results on the lepton universality of electrons and muons, the weak mixing angle sinθw, the W helicity and the study of the Triple Gauge Coupling. All the presented results are in agreement with the Standard Model predictions.

Single (anti-)top quark production in association with a lightest neutralino at the LHeC

In this paper we examine thoroughly the single (anti-)top quark production associated with a lightest neutralino at the possible CERN Large Hadron Electron Collider. We calculate the full next-to-leading order (NLO) QCD corrections to the process, including all the nonresonant diagrams, and do not assume the production and decay factorization for the possible resonant top squarks in the $R$-parity violating minimal supersymmetric standard model with 19 unrelated parameters. We investigate numerically the effects of the relevant supersymmetry parameters on the cross section, and present the transverse momentum distributions of the final (anti-)top quark at both the leading order (LO) and the QCD NLO. We find that the NLO QCD corrections enhance the LO cross sections in most chosen parameter space, and the NLO QCD impacts on the transverse momentum distributions of the final (anti-)top quark might be resolvable in some cases. We conclude that even with recently known experimental constraints on the supersymmetry parameters, the production rate could still achieve notable value in the admissible parameter space.