Inspire | HepData | arXiv:2209.07874 | ATLAS-TOPQ-2019-01
A measurement of observables sensitive to effects of colour reconnection in top-quark pair-production events is presented using 139 fb$^{-1}$ of 13 TeV proton--proton collision data collected by the ATLAS detector at the LHC. Events are selected by requiring exactly one isolated electron and one isolated muon with opposite charge and two or three jets, where exactly two jets are required to be $b$-tagged. For the selected events, measurements are presented for the charged-particle multiplicity, the scalar sum of the transverse momenta of the charged particles, and the same scalar sum in bins of charged-particle multiplicity. These observables are unfolded to the stable-particle level, thereby correcting for migration effects due to finite detector resolution, acceptance and efficiency effects. The particle-level measurements are compared with different colour reconnection models in Monte Carlo generators. These measurements disfavour some of the colour reconnection models and provide inputs to future optimisation of the parameters in Monte Carlo generators.
Inspire | HepData | ATLAS-TOPQ-2018-17 | Eur.Phys.J.C 80 (2020) 6, 528
The inclusive top quark pair ($t\bar{t}$) production cross-section $\sigma_{t\bar{t}}$ has been measured in proton-proton collisions at $\sqrt{s}=13$ TeV, using 36.1 fb$^{-1}$ of data collected in 2015-2016 by the ATLAS experiment at the LHC. Using events with an opposite-charge $e\mu$ pair and $b$-tagged jets, the cross-section is measured to be: $\sigma_{t\bar{t}} = 826.4 \pm 3.6$ (stat) $\pm 11.5$ (syst) $\pm 15.7$ (lumi) $\pm 1.9$ (beam) pb, where the uncertainties reflect the limited size of the data sample, experimental and theoretical systematic effects, the integrated luminosity, and the LHC beam energy, giving a total uncertainty of 2.4%. The result is consistent with theoretical QCD calculations at next-to-next-to-leading order. It is used to determine the top quark pole mass via the dependence of the predicted cross-section on $m_t^{\mathrm{pole}}$, giving $m_t^{\mathrm{pole}}=173.1^{+2.0}_{-2.1}$ GeV. It is also combined with measurements at $\sqrt{s}=7$ TeV and $\sqrt{s}=8$ TeV to derive ratios and double ratios of $t\bar{t}$ and $Z$ cross-sections at different energies. The same event sample is used to measure absolute and normalised differential cross-sections as functions of single-lepton and dilepton kinematic variables, and the results are compared with predictions from various Monte Carlo event generators.
Inspire | HepData | Eur.Phys.J. C77 (2017) no.4, 220 | doi:10.1140/epjc/s10052-017-4766-0 | arXiv:1610.09978
Measurements of jet activity in top-quark pair events produced in proton--proton collisions are presented, using 3.2 fb$^{-1}$ of $pp$ collision data at a centre-of-mass energy of 13 TeV collected by the ATLAS experiment at the Large Hadron Collider. Events are chosen by requiring an opposite-charge $e\mu$ pair and two $b$-tagged jets in the final state. The normalised differential cross-sections of top-quark pair production are presented as functions of additional-jet multiplicity and transverse momentum, $p_\text{T}$. The fraction of signal events that do not contain additional jet activity in a given rapidity region, the gap fraction, is measured as a function of the $p_\text{T}$ threshold for additional jets, and is also presented for different invariant mass regions of the $e\mu b\bar{b}$ system. All measurements are corrected for detector effects and presented as particle-level distributions compared to predictions with different theoretical approaches for QCD radiation. While the kinematics of the jets from top-quark decays are described well, the generators show differing levels of agreement with the measurements of observables that depend on the production of additional jets.
Inspire | HepData | J. High Energ. Phys. 149 (2019) | DOI:10.1007/JHEP02(2019)149 | arXiv:1811.06625v2 | CMS-TOP-17-014
Absolute and normalised differential top quark pair production cross sections are measured in the dilepton decay channels. The differential cross sections have been obtained by the CMS experiment at the CERN LHC in 2016 in proton-proton collisions at a centre-of-mass energy of 13 TeV. The measurements are performed with data corresponding to an integrated luminosity of 35.9/fb. The cross sections are measured differentially as a function of the kinematic properties of the top quarks and the tt system at the particle and parton levels, and the top quark decay products at the particle level. The results are compared to Monte Carlo simulations from POWHEG interfaced with the parton shower generators PYTHIA 8 and HERWIG 7 up to NNLO (next-to-next leading order) accuracy.
Inspire | HepData | JHEP 1804 (2018) 060 | DOI:10.1007/JHEP04(2018)060 | arXiv:1708.07638 | https://www.hepdata.net/record/81686 | CMS-TOP-16-007
Abstract: Normalized differential cross sections for top quark pair production are measured in the dilepton ($e^{+}e^{-}$, $\mu^{+}\mu^{-}$, and $\mu^{\mp}e^{\pm}$) decay channels in proton-proton collisions at a center-of-mass energy of 13TeV. The measurements are performed with data corresponding to an integrated luminosity of 2.1$fb^{-1}$ using the CMS detector at the LHC. The cross sections are measured differentially as a function of the kinematic properties of the leptons, jets from bottom quark hadronization, top quarks, and top quark pairs at the particle and parton levels. The results are compared to several Monte Carlo generators that implement calculations up to next-to-leading order in perturbative quantum chromodynamics interfaced with parton showering, and also to fixed-order theoretical calculations of top quark pair production up to next-to-next-to-leading order. Rivet: This analysis is to be run on $\text{t}\bar{\text{t}}$ Monte Carlo. The particle-level phase space is defined using the following definitions: \begin{description} \item[lepton]: an electron or muon with $p_\text{T}>30\,\text{GeV}$ and $|\eta|<2.4$, dressed within a cone of radius 0.1, \item[jet]: a jet is reconstructed with the anti-$k_t$ algorithm with a radius of 0.4, after removing the neutrinos and dressed leptons, with $p_\text{T]>30\,\text{GeV}$ and $|\eta|<2.4$, \item[b-jet]: a jet that contains a B-hadron. \end{description} A W boson at the particle level is defined by combining a dressed lepton and a neutrino. In each event, a pair of particle-level W bosons is chosen among the possible combinations such that the sum of the absolute values of the invariant mass differences with respect to the W boson mass is minimal. Similarly, a top quark at the particle level is defined by combining a particle-level W boson and a b jet. The combination of a W boson and a b jet with the minimum invariant mass difference from the correct top quark mass is selected.
Generic analysis of typical per-particle distributions such as $\eta$, $y$, $pT$, $\phi$, etc.
Only partons (excluding top quarks) are taken into account to construct a kt cluster sequence. Thus this analysis can be used as a generic validation tool for QCD activity.
This is a pure Monte Carlo study for $t\bar{t}$ production.