The new ATLAS Fast Calorimeter Simulation

With the huge amount of data collected with ATLAS, there is a need to produce a large number of simulated events. These productions are very CPU and time consuming when using the full GEANT4 simulation. FastCaloSim is a program to quickly simulate the ATLAS calorimeter response, based on a parameterization of the GEANT4 energy deposits of several kinds of particles in a grid of energy and eta. A new version of FastCaloSim is under development and its integration into the ATLAS simulation infrastructure is ongoing. The use of machine learning techniques improves the performance and decreases the memory usage. Dedicated parameterizations for the forward calorimeters are being studied. First results of the new FastCaloSim show substantial improvements of the description of energy and shower shape variables, including the variables for jet substructure

Inclusive and differential ttˉ\bar{\rm t} cross-sections in ATLAS

This presentation contains the latest results from inclusive and differential t$\bar{\rm t}$ cross-sections measurements in the ATLAS experiment

Inclusive and differential ttˉt\bar{t} cross-sections in ATLAS experiment

The latest results of inclusive and differential $t\bar{t}$ cross-section measurements in the ATLAS experiment at CERN are presented. Measurements are based on analyses of $\sqrt{s}=13$ TeV proton-proton stable collisions collected by the ATLAS detector, with corresponding integrated luminosities of 36.1 fb$^{-1}$ or 139 fb$^{-1}$. This includes inclusive cross-section measurements in the dilepton $e\mu$ and the lepton+jets channel, which achieved significant improvements in the precision due to larger data statistics and more sophisticated techniques used. Results of $t\bar{t}$ differential cross-section measurements in three main $t\bar{t}$ system decay channels: dilepton, lepton+jets and all-hadronic resolved, are also presented. Measurement in the all-hadronic resolved channel was performed for the first time in the ATLAS experiment. All differential measurements provide double-differential spectra which allow to determine correlations between variables and which allow stringent tests of the Standard Model

Measurements of ttˉ\text{t}\bar{\text{t}} differential cross-sections of highly boosted top quarks decaying to all-hadronic final states in pp collisions at s=13 TeV\sqrt{s} = 13\ \text{TeV} using the ATLAS detector

Measurements are presented of the highly boosted top-quark pair production differential cross-section in 13 TeV pp collisions in the all-hadronic decay mode, using 36.1 fb$^{-1}$ of data collected by the ATLAS detector in 2015 and 2016. The tt ̄ process is measured by requiring two top-quark candidates, one with pT > 500 GeV and a second with pT > 350 GeV, with each candidate reconstructed as anti-kt jets with radius parameter R = 1.0. The top-quark candidates are separated from the multijet background using the jet substructure and the presence of a b-quark tag in each jet. The observed kinematic distributions are unfolded to recover the differential cross-sections in a fiducial phase-space region at the particle-level. The observed distributions are also unfolded to obtain the differential cross-sections at the parton-level for a similar phase-space region. The particle-level and parton-level unfolded differential cross-sections are compared with several Standard Model Monte Carlo predictions

Differential ttˉt\bar{t} cross-section measurements using boosted top quarks with 139 fb−1^{-1} of ATLAS data

Preliminary results of two differential cross-section measurements in the ATLAS experiment at CERN are presented. Measurements are focused on the top-antitop pair production in the lepton+jets and the all-jets 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 in 2015-2018, corresponding to an integrated luminosity of 139 fb$^{-1}$. Measured spectra are compared with the Standard Model predictions and they are used to set limits on the Wilson coefficients of the effective field theory extension of the Standard Model

Measurements of ttˉt\bar{t} differential cross-sections of highly boosted top quarks decaying to all-hadronic final states in pppp collisions at s=13 \sqrt{s}=13\, TeV using the ATLAS detector

Measurements are made of differential cross-sections of highly boosted pair-produced top quarks as a function of top-quark and $t\bar{t}$ system kinematic observables using proton--proton collisions at a center-of-mass energy of $\sqrt{s} = 13$ TeV. The data set corresponds to an integrated luminosity of $36.1$ fb$^{-1}$, recorded in 2015 and 2016 with the ATLAS detector at the CERN Large Hadron Collider. Events with two large-radius jets in the final state, one with transverse momentum $p_{\rm T} > 500$ GeV and a second with $p_{\rm T}>350$ GeV, are used for the measurement. The top-quark candidates are separated from the multijet background using jet substructure information and association with a $b$-tagged jet. The measured spectra are corrected for detector effects to a particle-level fiducial phase space and a parton-level limited phase space, and are compared to several Monte Carlo simulations by means of calculated $\chi^2$ values. The cross-section for $t\bar{t}$ production in the fiducial phase-space region is $292 \pm 7 \ \rm{(stat)} \pm 76 \rm{(syst)}$ fb, to be compared to the theoretical prediction of $384 \pm 36$ fb

Measurements of ttˉt\bar{t} differential cross-sections of highly boosted top quarks decaying to all-hadronic final states in pppp collisions at s=13 \sqrt{s}=13\, TeV using the ATLAS detector

Measurements are made of differential cross-sections of highly boosted pair-produced top quarks as a function of top-quark and $t\bar{t}$ system kinematic observables using proton--proton collisions at a center-of-mass energy of $\sqrt{s} = 13$ TeV. The data set corresponds to an integrated luminosity of $36.1$ fb$^{-1}$, recorded in 2015 and 2016 with the ATLAS detector at the CERN Large Hadron Collider. Events with two large-radius jets in the final state, one with transverse momentum $p_{\rm T} > 500$ GeV and a second with $p_{\rm T}>350$ GeV, are used for the measurement. The top-quark candidates are separated from the multijet background using jet substructure information and association with a $b$-tagged jet. The measured spectra are corrected for detector effects to a particle-level fiducial phase space and a parton-level limited phase space, and are compared to several Monte Carlo simulations by means of calculated $\chi^2$ values. The cross-section for $t\bar{t}$ production in the fiducial phase-space region is $292 \pm 7 \ \rm{(stat)} \pm 76 \rm{(syst)}$ fb, to be compared to the theoretical prediction of $384 \pm 36$ fb