No Arabic abstract
The collective phenomena are observed not only in heavy ion collisions, but also in the proton-nucleus and in high-multiplicity $pp$ collisions. The latest results from this area obtained in ATLAS are presented. In $p$+Pb collisions the emission source of particles is measured using the HBT method. The analysis of $p$+Pb data collected in 2016 provides information on the elliptic flow of charged hadrons and muons. Low multiplicity events from $pp$, $p$+Pb and peripheral Pb+Pb collisions are studied with the cumulant methods. A deeper understanding of Pb+Pb collisions is provided by the analysis of longitudinal fluctuations of the collective flow parameters.
We present first results from the ATLAS Zero Degree Calorimeters (ZDC) based on 7~TeV pp collision data recorded in 2010. The ZDC coverage of +/-~350 microradians about the forward direction makes possible the measurement of neutral particles (primarily pi0s and neutrons) over the kinematic region x_F >~0.1 and out to p_T<~ 1.2 GeV/c at large x_F. The ATLAS ZDC is unique in that it provides a complete image of both electromagnetic and hadronic showers.This is illustrated with the reconstruction of pi0s with energies of 0.7-3.5 TeV. We also discuss the waveform reconstruction algorithm which has allowed good time-of-flight resolution on leading neutrons emerging from the collisions despite the sparse (40 MHz) sampling of the calorimeter signals used.
Recent measurements of top quark properties using $t{bar t}$ events produced in proton-proton collisions at the Large Hadron Collider with centre of mass energies of 7 and 8 TeV and detected by the ATLAS experiment are presented. These results include top quark mass, the top and anti-top mass difference, the electric charge, the top quark polarization and spin correlation, the $t{bar t}$ charge asymmetry and the search for flavour changing neutral currents.
An overview is given of the results on charmonium production obtained by the ATLAS collaboration at the LHC. Recent preliminary measurements covering prompt and non-prompt production of $J/psi$ and $psi(2S)$ states in the range of high transverse momenta from 60 to 360~GeV are highlighted.
Various aspects of forward physics have been studied by the ATLAS collaboration using data from Run I at the LHC. In this text, main results of three published analyses are summarized, based on data from proton-proton collisions at $sqrt{s} = 7$ or 8 TeV collected between 2010 and 2012. One analysis deals with diffractive signature with at least two jets in the final state, the other two study exclusive production of a pair of leptons or W bosons.
We present results on the Central Exclusive Production of charged particle pairs $h^{+}h^{-}$ ($h = pi, K, p$), $ppto p^prime+h^{+}h^{-}+p^prime$, obtained with the STAR experiment at RHIC in proton-proton collisions at a center-of-mass energy of $sqrt{s} = 200$ GeV. All final-state particles were reconstructed, including forward-scattered protons detected in the Roman Pot system. As a result, the Double Pomeron Exchange (DPE) events were selected and the non-exclusive backgrounds were efficiently rejected. Differential fiducial cross sections were measured as functions of observables related to the central hadronic final state and to the forward-scattered protons. The measured cross sections were compared to phenomenological model predictions based on the DPE. We also present preliminary results on the measurement of the same physics process at higher collision energy $sqrt{s} = 510$ GeV. The data demonstrate features similar to those observed at $sqrt{s} = 200$ GeV.