The ATLAS potential for the study of the top quark properties and physics beyond the Standard Model in the top quark sector, is described. The measurements of the top quark charge, the spin and spin correlations, the Standard Model decay (t-> bW), rare top quark decays associated to flavour changing neutral currents (t-> qX with X = gluon, Z, photon) and ttbar resonances are discussed. The sensitivity of the ATLAS experiment is estimated for an expected luminosity of 1fb-1 at the LHC. The full simulation of the ATLAS detector is used. For the Standard Model measurements the expected precision is presented. For the tests of physics beyond the Standard Model, the 5 sigma discovery potential (in the presence of a signal) and the 95% Confidence Level (CL) limit (in the absence of a signal) are given.
The observation of the top quark will be an important milestone in ATLAS. This talk reviews methods that ATLAS plans to use to observe the top quark pair production process and measure its cross section.
These proceedings present the first observation of single top-quark production associated with a photon using the full Run2 proton-proton dataset collected by the ATLAS experiment at the LHC.
Amongst the first physics results of the ATLAS detector at LHC will be an analysis of Jpsi and Upsilon production. Even at low luminosity ATLAS will quickly start improving on current quarkonia measurements providing world leading results with around 10 pb-1 of data. The narrow quarkonia resonances will also be used as tools for alignment and calibration of the trigger and tracking systems.
A review of the main recent results on top quark production from the ATLAS and CMS experiments is presented. Results on both electroweak single top quark production and strong top pair production are presented.
The top-quark mass measurements carried out by the LHC experiments, ATLAS and CMS, are summarized. Results of different approaches to the top-quark mass reconstruction are presented. Masses from different measurements are in good agreement within uncertainties. Precision of the measurements with the directly measured top-quark mass is now better than 0.5%. Progress in determination of the top-quark pole mass is reported and the relation between the directly measured top-quark mass and top-quark pole mass is discussed.
The top-quark mass is one of the fundamental parameters of the Standard Model of particle physics. The latest ATLAS measurements of the top-quark mass in top quark pair final states are presented. Measurements use di-lepton, lepton+jets and all-jets final states and their combination is performed. Measurements of the top-quark pole mass based on precision theoretical QCD calculations for lepton kinematic distribution and for top quark pair production with an additional jet are also presented.
This article presents a review of recent results on direct top quark mass measurements performed by the ATLAS and CMS collaborations on $pp$ collisions collected during Run 2 of the LHC at $\sqrt{s}=$13 TeV.
Recent results on top-quark mass measurements with the ATLAS detector using proton-proton collisions at the Large Hadron Collider are presented. These results correspond to the measurements in the $t\bar{t}$ all-hadronic and dilepton channels at $\sqrt{s} = 8\ \mathrm{TeV}$ collisions and an integrated luminosity of $20\ \mathrm{fb}^{-1}$.
Latest results on inclusive top-quark pair production cross-sections are presented using collision data collected by ATLAS and CMS experiments at the LHC. Inclusive and differential measurements of top-quark pair production cross-sections from ATLAS and CMS are presented in the resolved and boosted kinematic regions. The cross-sections are measured as a function of various kinematic observables of the top quarks, the jets and leptons of the event final state.
A search for new heavy quarks focusing on recent vector-like quark searches with the ATLAS detector at the CERN Large Hadron Collider is presented. Two recent searches targeting the pair production of type vector-like quarks are described. The first search is sensitive to vector-like up-type quark ($T$) decays to a $t$ quark and either a Standard Model Higgs boson or a $Z$ boson. The second search is primarily sensitive to $T$ decays to $W$ boson and a $b$ quark. Additionally, the results can be interpreted for alternative VLQ decays.
Top quark physics measurements performed using data from the ATLAS detector at the LHC rely on efficient reconstruction and precise calibration of leptons, jets and missing transverse energy. A review of the techniques used to reconstruct such objects is given, with an emphasis on the uncertainties achieved for energy calibration and efficiency measurements, illustrated with their impact on key top quark physics results.
One of the first physics results to come out of ATLAS will be an analysis of J/psi and Upsilon production at 14 TeV. I give an overview of the motivation for looking at the theoretical model underlying quarkonium production, ATLAS expected performance and rates for quarkonium reconstruction and ability to separate out various proposed production models with a view to improving our understanding of QCD.
The top quark mass measurement with ATLAS in the lepton plus jets channel is summarized from the perspective of the early data. Using the invariant mass of the three jets arising from the hadronic side as the estimator of the top quark mass, a precision of the order of 1 to 3.5 GeV on the top quark mass measurement should be achievable, assuming a jet energy scale uncertainty of 1 to 5%.
Recent results on top quark modelling and tuning are presented. In particular, the focus of this talk is on the studies on the definition and commissioning of the common Monte Carlo effort carried out by ATLAS and CMS within the LHCtopWG. An overview of current recommendations for modelling uncertainties is also presented.
Many models beyond the standard model predict the existence of vector-like quarks or other types of heavy resonances. Using proton-proton collision data at center-of-mass energies of 8 and 13 TeV, the ATLAS and CMS Collaborations have performed a multitude of searches for pair and singly produced vector-like quarks decaying to W, Z, or Higgs bosons. Heavy gauge and (pseudo)scalar resonances decaying to top quarks have been searched for as well. No evidence for any of these hypothetical particles has been found yet, and stringent exclusion limits are derived on their masses, cross sections and …
The top quark is the heaviest known fundamental particle. As it is the only quark that decays without hadronisation, it provides the unique opportunity to probe the properties of bare quarks at the Large Hadron Collider (LHC). This article will present two recent measurements of the top quark using 13TeV collision data with the ATLAS experiment: the top and anti-top quark pair charge asymmetry measurement alongside the first test of lepton flavour universality (LFU) of leptons to W bosons from tt events.
An overview of recent searches with top quarks in the final state using up to 36 fb$^{-1}$ of pp collision data at $\sqrt{s}$ = 13 TeV collected with the ATLAS and CMS experiments at the LHC is presented. In particular, searches for heavy resonances decaying into third generation quarks, searches for production of vector-like quarks and searches for dark-matter produced in association with top quarks are summarised. No significant excess over the SM prediction is found and 95% CL exclusion limits are set in a variety of models.
The most recent results of the top-quark mass measurements with the ATLAS detector using data collected from proton-proton collisions at the Large Hadron Collider are presented. Although several decay modes of the top-quark pairs have been used in ATLAS for top-quark mass measurements, only the latest results are presented (single lepton and dilepton channels). The top-quark pole mass from the $t\overline{t}$ cross-section measurement in the dilepton channel and the top-antitop mass difference measurement in the single-lepton channel are also shown. The systematic uncertainties associated to t…
Recent analyses of top quark production in association with vector bosons are summarized, representing the most precise inclusive and differential cross section measurements of these processes to date. Proton-proton collision data at a center-of-mass energy of $\sqrt{s}=13$ TeV, recorded by the ATLAS and CMS detectors at the LHC are analyzed, corresponding to an integrated luminosity of up to 139 fb$^{-1}$ for each experiment. Comparisons with theory calculations are performed and overall good agreement with standard model predictions are obtained.
The ATLAS and CMS Collaborations have performed a variety of measurements of the top quark mass, taking advantage of the abundant production of top quarks at the LHC. The most recent measurements are reported here, based on data collected at 8 and 13 TeV, with particular emphasis on the distinction between the so-called "direct" measurements and the "indirect" evaluations obtained from cross sections and differential cross sections.
An accurate determination of the top quark pair production cross section at the LHC provides a valuable check of the Standard Model. Given the high statistics which will be available (about one top quark pair per second, at a luminosity of 10^33 cm^-2 s^-1), this check can be performed relatively fast after the turn on of the LHC. The prospects for measuring the total top quark pair cross section with the ATLAS detector during the initial period of LHC running will be presented here. The cross section is determined in the single lepton channel and in the dilepton channel.
ATLAS has made several measurements of the top quark mass using proton-proton collision data recorded in 2012 at the LHC with a centre-of-mass energy of 8 TeV. Those summarised here include an indirect determination of the top quark pole mass from lepton differential cross-sections; previous direct measurements of the top quark mass in the $t\bar{t}\to\textrm{dilepton}$ and $t\bar{t}\to\textrm{all-jets}$ decay channels as well as in the $t$-channel of single-top-quark production; and lastly, the new direct measurement of the top quark mass in the $t\bar{t}\to\textrm{lepton+jets}$ decay channel…
This article presents measurements of all three single top-quark production channels. Detailed measurements of $t$-channel single top-quark production using data collected by the ATLAS experiment in proton--proton collisions at a centre-of-mass energy of 8 TeV are shown as well es first results using 13 TeV at the LHC. The associated production of a top quark and a $W$ boson is presented for data collected at 13 TeV, while the first evidence of single top-quark production in the $s$-channel is shown for data collected at 8 TeV.
Measurements of the branching ratios of top quark decays into leptons and jets using events with $t \overline{t}$ (top antitop) pairs are reported. Events were recorded with the ATLAS detector at the LHC in pp collisions at a center-of-mass energy of 7 TeV. The collected data sample corresponds to an integrated luminosity of 4.6 ${\mathrm{fb}}^{-1}$. The measured top quark branching ratios agree with the Standard Model predictions within the measurement uncertainties of a few percent.
The search for first top-quark pair candidate events and the related background studies using data-driven techniques are reported for about 300 inverse nb of 7 TeV proton-proton collision data delivered by the Large Hadron Collider (LHC) and collected with the ATLAS detector. Selected events are characterized by the presence of high-pT isolated charged lepton(s), high jet multiplicity, jet(s) identified as originating from b-quark by a secondary vertex tagger algorithm, and missing transverse energy. They reveal kinematics properties consistent with top pair production.
The pair production of heavy fourth-generation quarks, which are predicted under the hypothesis of flavor democracy, is studied using tree-level Monte Carlo generators and fast detector simulation. Two heavy-quark mass values, 500 and 750$\gev$, are considered with the assumption that the fourth family mixes primarily with the two light families. It is shown that a clear signature will be observed in the data collected by the ATLAS detector, after the first year of low-luminosity running at the Large Hadron Collider.
A search is performed for top quark pairs with early data of ATLAS pp collision taken at {\surd}s = 7 TeV. Several candidate events are observed, in both lepton plus jets and dilepton channels. The properties of these events are described, and compared to the expectations from Monte Carlo simulation. A first study of the backgrounds in the lepton plus jets channel is presented including a data-driven determination of the contribution of QCD multi-jet events.
The charge asymmetry in top quark pair production in the di-lepton $t\bar t$ channel using the ATLAS experiment at Large Hadron Collider is presented. The asymmetry is studied in the distribution of absolute rapidity difference between top and anti-top. The reconstruction of the $t\bar t$ system is based on a leading order matrix element. The lepton charge asymmetry is also presented. All results are consistent with the Standard Model.
A set of measurements of top quark pair and single top quark production in association with standard model (SM) bosons performed by the CMS and ATLAS Collaborations is presented. The consistency of these results among themselves and with the SM prediction is discussed. The latest results on four top quark production are also shown.
Top quarks are produced copiously at the LHC, and a variety of related measurements has been made in the recent years by the two collaborations ATLAS and CMS. The most recent measurements of the top quark mass by the two collaborations are reported here. The top quark mass has been measured with a relative uncertainty smaller than 0.3%, making the top quark the most accurately measured quark.
A QCD analysis is reported of ATLAS data on inclusive W and Z boson production in pp collisions at the LHC, jointly with ep deep inelastic scattering data from HERA. The ATLAS data exhibit sensitivity to the light quark sea composition and magnitude at Bjorken x ~ 0.01. Specifically, the data support the hypothesis of a symmetric composition of the light quark sea at low x. The ratio of the strange-to-down sea quark distributions is determined to be 1.00(+0.25-0.28) at absolute four-momentum transfer squared Q^2 = 1.9 GeV^2 and x = 0.023.
The production of top quarks through single or rare production modes has become important due to the large amount of data collected by both ATLAS and CMS at the LHC. Many searches are now studying these processes either as a targeted signal or as an important source of background. This document reviews the Monte Carlo simulations used to model these processes in ATLAS and CMS, and how the modeling systematic uncertainties are estimated. Many analyses have also recently released a large variety of unfolded distributions. These distributions are shown and the modeling from various Monte Carlo ge…
We present recent measurements of the top quark mass by the ATLAS and CMS experiments in the $\mathrm{t}\overline{\mathrm{t}}$ lepton+jets, all-hadronic, and dilepton channels. In addition, we present a measurement using a topology enriched in t-channel single top events. The analyses include observables whose sensitivity to the top mass is calibrated using Monte Carlo simulation before they are utilized to extract the value of $\mathrm{m}_{\mathrm{t}}$ in data. The measurements outlined here enter into recent combinations by ATLAS and CMS that yield a sub-GeV precision on the top mass.
These proceedings highlight a selection of recent ATLAS and CMS measurements which target either the production of a single top quark or the associated production of a top-antitop quark pair together with a $W$ boson, a $Z$ boson, or a photon ($γ$). The highlighted analyses are based predominantly on proton-proton collision data collected by the two experiments during Run 2 of the LHC at a centre-of-mass energy of $\sqrt{s}=13$ TeV with datasets corresponding to integrated luminosities of up to 77.5 fb$^{-1}$. One combination of ATLAS and CMS single top quark measurements employing the full Ru…
Analyses of single top-quark production via $tW$ production, via $tZq$ production, and in the $s$-channel are presented, showing the scope of recent ATLAS and CMS analyses of $pp$ collisions produced at the LHC at $\sqrt{s}=7,8$, and ${13}\,\text{TeV}$. Cross-section values and signal significance estimates are established, confirming good agreement with the most precise available fixed-order calculations for each production mode.
A review is presented of the most recent measurements of top quark strong and electroweak production performed by using data collected with the ATLAS detector in proton-proton collisions at sqrt(s) = 7 and 8 TeV at the Large Hadron Collider corresponding to integrated luminosities of up to about 4.7/fb and 20/fb, respectively.
The large ttbar production cross-section at the LHC suggests the use of top quark decays to calibrate several critical parts of the detectors, such as the trigger system, the jet energy scale and b-tagging.
Results of top-quark mass measurements in the di-lepton and the all-jets top-antitop decay channels with the ATLAS detector are presented. The measurements are obtained using proton-proton collisions at a centre-of-mass energy $\sqrt{s}$ = 8 TeV at the CERN Large Hadron Collider. The data set used corresponds to an integrated luminosity of 20.2 $fb^{-1}$. The top-quark mass in the di-lepton channel is measured to be 172.99 $\pm$ 0.41 (stat.) $\pm$ 0.74 (syst.) GeV. In the all-jets analysis, the top-quark mass is measured to be 173.72 $\pm$ 0.55 (stat.) $\pm$ 1.01 (syst.) GeV. In addition, the …
An overview of the most recent results on top quark physics obtained using proton-proton collision data collected with the ATLAS and the CMS experiments at 7 TeV center-of-mass energy is given. Measurements for inclusive and differential top quark pair or single top quark production in different final states are reviewed. Top properties such as W helicity in top decays, electric charge, charge asymmetry and spin correlations of top quark pairs, among others have also been measured by the LHC experiments. All the measurements are found to be consistent with the Standard Model predictions with a…
A measurement of the top quark mass in topologies enhanced with single top quarks produced in the $t$-channel produced via weak interactions is presented. The dataset was collected at a centre-of-mass energy of $\sqrt{s}=8\,\mathrm{TeV}$ with the ATLAS detector at the LHC and corresponds to an integrated luminosity of $20.3\,\mathrm{fb^{-1}}$. To determine the top quark mass a template method is used based on the distribution of the invariant mass of the lepton and the $b$-tagged jet as estimator. The result of the measurement is $m_{\mathrm{top}} = 172.2 \pm 0.7 {\mathrm{(stat.)}} \pm 2.0 {\m…
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 measure…
We present studies of the production and spectroscopy of some members of the B-hadron family. We reconstruct B ground states in their hadronic decay modes with a J/ψ or Υ in the final state. These studies are based on the 2011 7 TeV dataset collected by the ATLAS detector.
With the large data set delivered during the second run of the CERN LHC, inclusive and differential measurements of the top quark-antiquark production cross section at the ATLAS and CMS experiments often reach a precision that is comparable or superior to that of the corresponding theoretical calculations. The results of these measurements can be used to test the validity of perturbative quantum chromodynamics (QCD), and to precisely extract the values of parameters of the QCD Lagrangian such as the top quark mass ($m_\mathrm{t}$). The value of $m_\mathrm{t}$ can also be measured, with higher …
Recent measurements of top quark properties with ${\rm t{\bar t}}$ events collected by the ATLAS experiment in proton-proton collisions at the center of mass energy $\sqrt{s}=8$ and $13$ TeV, are presented. The measurements of the top quark width, spin and spin correlations, polarisation, the $W$ boson helicity fractions, charge and CP asymmetries are discussed. Finally, recent results obtained on colour flow effects in ${\rm t{\bar t}}$ events are presented. All the measurements are consistent with the Standard Model expectations.
Measurements of the top quark production cross section in proton-proton collisions with the ATLAS detector at the Large Hadron Collider are presented. The measurements require no, one or two electrons or muons in the final state (single lepton, dilepton, hadronic channel). In addition, the decay modes with tau leptons are tested (channels with tau leptons). The main focus is on measurements of differential spectra of $t\bar{t}$ final states, in particular, measurements that are able to constrain the modelling of additional parton radiation like the jet multiplicity distribution.
Preliminary results of two differential cross-section measurements in the ATLAS experiment at CERN are presented. Measurements are focused on the top-antitop quark pair production in the~lepton+jets and the~all-hadronic channels in the kinematic region with high transverse momentum top quarks. Both measurements use the full Run 2 data of 13 TeV proton-proton collisions from the Large Hadron Collider collected by the ATLAS detector in 2015-2018, corresponding to an integrated luminosity of 139 fb$^{-1}$. The measured spectra are compared with the Standard Model predictions. They are also used t…
The latest measurements of the top quark mass obtained by the ATLAS and CMS experiments at the LHC for centre-of-mass energies of 7 and 8 TeV are presented. The mass of the top quark is measured using several methods and channels, including the reconstructed invariant mass distribution of the top quark and shapes of top quark decay distributions. Measurements based on the inclusive tt-bar cross section and novel observables based on the differential cross section in the tt-bar + 1 jet channel are also discussed. The results of the various channels are combined and compared to the world average…
Summary of first ATLAS results is given for the Standard Model Higgs boson in the mass range 110 < mH < 130 GeV, when produced in association with a W/Z boson and decaying to a pair of b-quarks. No evidence for the Higgs boson production is observed in a dataset of proton-proton collisions at a center of mass energy of 7 TeV and corresponding to 1.04 fb-1 of integrated luminosity, recorded by the ATLAS experiment at the LHC in 2011. Upper limits on Higgs boson production cross sections for the channels considered are presented.
Top-quark pairs in association with final state particles are produced in large quantities at the LHC due to the high centre-of-mass energy available in proton-proton collisions. One such topology is that of a prompt photon radiated from the top quark in addition to the final state particles from the top quark decay. Using 36.1 fb$^{-1}$ of data collected at $\sqrt{s}$ = 13 TeV with the ATLAS detector, fiducial cross-section results are shown in the single-lepton and dilepton channels. Object-level and event-level neural networks are used to increase sensitivity.
Precise measurements of the properties of the top quark test the Standard Model (SM) and can be used to constrain new physics models. The top quark pair charge asymmetry is an asymmetry predicted to occur beyond leading-order QCD in the SM, and may be significantly enhanced by the presence of new physics. The $t\bar{t}$ production charge asymmetry is measured inclusively and differentially using the 8 TeV ATLAS dataset in the lepton+jets final state, including a dedicated measurement for highly boosted top quarks. The results are in agreement with the SM and compared to new physics models. The…
Absolute and normalised differential cross-sections of single top quarks produced in the $t$-channel are presented. 20.2 fb$^{-1}$ of proton-proton collision data at a centre-of-mass energy of 8 TeV collected by the ATLAS experiment at the LHC are used. Differential cross-sections as a function of the transverse momentum and the absolute value of the rapidity of the top quarks and the top antiquarks are measured at both parton level and particle level. The transverse momentum and rapidity differential cross-sections of the scattered light-quark jets are extracted at particle level. The measure…
