Top physics on ATLAS

The top quark is the heaviest known fundamental particle. As it is the only quark that decays before it hadronizes, this gives us the unique opportunity to probe the properties of bare quarks. This talk will focus on a few recent precision measurements by the ATLAS Collaboration of the top quark: fiducial top pair and single top production cross sections including differential distributions will be presented alongside some top quark properties measurements. Interpretations in terms of limits on beyond the standard model and searches for new physics using top quarks will also be presented

Top physics in ATLAS

These proceedings summarize the latest measurements on top production, top properties and searches using the ATLAS detector at the LHC. The measurements are performed on $pp$ collision data with a center of mass energy $\sqrt{s} = 7, 8$ and $13$ TeV

Measurements of the charge asymmetry in top-quark pair production in the dilepton final state at s=8\sqrt{s}=8 TeV with the ATLAS detector

Measurements of the top--antitop quark pair production charge asymmetry in the dilepton channel, characterized by two high-${p}_{\rm{T}}$ leptons (electrons or muons), are presented using data corresponding to an integrated luminosity of 20.3 $\textrm{fb}^{-1}$ from $pp$ collisions at a center-of-mass energy $\sqrt{s} = 8$~TeV collected with the ATLAS detector at the Large Hadron Collider at CERN. Inclusive and differential measurements as a function of the invariant mass, transverse momentum, and longitudinal boost of the $t\bar{t}$ system are performed both in the full phase space and in a fiducial phase space closely matching the detector acceptance. Two observables are studied: $A_C^{\ell \ell}$ based on the selected leptons and $A_C^{t\bar{t}}$ based on the reconstructed $t\bar{t}$ final state. No significant deviation from the Standard Model expectations is observed

Search for narrow resonances using the dijet mass spectrum in pp collisions at s√=8 TeV

Results are presented of a search for the production of new particles decaying to pairs of partons (quarks, antiquarks, or gluons), in the dijet mass spectrum in proton-proton collisions at s√=8  TeV. The data sample corresponds to an integrated luminosity of 4.0  fb−1, collected with the CMS detector at the LHC in 2012. No significant evidence for narrow resonance production is observed. Upper limits are set at the 95% confidence level on the production cross section of hypothetical new particles decaying to quark-quark, quark-gluon, or gluon-gluon final states. These limits are then translated into lower limits on the masses of new resonances in specific scenarios of physics beyond the standard model. The limits reach up to 4.8 TeV, depending on the model, and extend previous exclusions from similar searches performed at lower collision energies. For the first time mass limits are set for the Randall–Sundrum graviton model in the dijet channel

Measurement and QCD analysis of double-differential inclusive jet cross-sections in pp collisions at s=8\sqrt{s} = 8 TeV and ratios to 2.76 and 7 TeV

A measurement of the double-differential inclusive jet cross section as a function of the jet transverse momentum pT and the absolute jet rapidity abs(y) is presented. Data from LHC proton-proton collisions at $\sqrt{s} = 8$ TeV, corresponding to an integrated luminosity of 19.7 inverse-femtobarns, have been collected with the CMS detector. Jets are reconstructed using the anti-$k_T$ clustering algorithm with a size parameter of 0.7 in a phase space region covering jet $p_T$ from 74 GeV up to 2.5 TeV and jet absolute rapidity up to $(y)$ = 3.0. The low-$p_T$ jet range between 21 and 74 GeV is also studied up to $(y)$ = 4.7, using a dedicated data sample corresponding to an integrated luminosity of 5.6 inverse-picobarns. The measured jet cross section is corrected for detector effects and compared with the predictions from perturbative QCD at next-to-leading order (NLO) using various sets of parton distribution functions (PDF). Cross section ratios to the corresponding measurements performed at 2.76 and 7 TeV are presented. From the measured double-differential jet cross section, the value of the strong coupling constant evaluated at the Z mass is $\alpha_{S}(M_{Z})$ = 0.1164$^{+0.0060}_ {0.0043}$, where the errors include the PDF, scale, nonperturbative effects and experimental uncertainties, using the CT10 NLO PDFs. Improved constraints on PDFs based on the inclusive jet cross section measurement are presented