96 research outputs found

    Multiplicity dependence of the average transverse momentum in pp, p-Pb, and Pb-Pb collisions at the LHC

    Get PDF
    The average transverse momentum versus the charged-particle multiplicity NchN_{ch} was measured in p-Pb collisions at a collision energy per nucleon-nucleon pair sNN\sqrt{s_{NN}} = 5.02 TeV and in pp collisions at collision energies of s\sqrt{s} = 0.9, 2.76, and 7 Tev in the kinematic range 0.15 with NchN_{ch} is observed, which is much stronger than that measured in Pb-Pb collisions. For pp collisions, this could be attributed, within a model of hadronizing strings, to multiple-parton interactions and to a final-state color reconnection mechanism. The data in p-Pb and Pb-Pb collisions cannot be described by an incoherent superposition of nucleon-nucleon collisions and pose a challenge to most of the event generators.publishedVersio

    Energy dependence of the transverse momentum distributions of charged particles in pp collisions measured by ALICE

    Get PDF
    Differential cross sections of charged particles in inelastic pp collisions as a function of pTp_T have been measured at s\sqrt{s} = 0.9, 2.76 and 7 TeV at the LHC. The pTp_T spectra are compared to NLO-pQCD calculations. Though the differential cross section for an individual s\sqrt{s} cannot be described by NLO-pQCD, the relative increase of cross section with s\sqrt{s} is in agreement with NLO-pQCD. Based on these measurements and observations, procedures are discussed to construct pp reference spectra at s\sqrt{s} = 2.76 and 5.02 TeV up to pTp_T = 50 GeV/c as required for the calculation of the nuclear modification factor in nucleus-nucleus and proton-nucleus collisions.publishedVersio

    Charmonium and e+ee^+e^- pair photoproduction at mid-rapidity in ultra-peripheral Pb-Pb collisions at sNN\sqrt{s_{NN}} = 2.76 TeV

    Get PDF
    The ALICE Collaboration at the LHC has measured the J/ψJ/\psi and ψ\psi' photoproduction at mid-rapidity in ultra-peripheral Pb-Pb collisions at sNN\sqrt{s_{NN}} = 2.76 TeV. The charmonium is identified via its leptonic decay for events where the hadronic activity is required to be minimal. The analysis is based on an event sample corresponding to an integrated luminosity of about 23 μb1{\mu}b^{-1}, The cross section for coherent and incoherent J/ψJ/\psi production in the rapidity interval -0.9 < y < 0.9, are dσJ/ψcoh/dy=2.380.24+0.34(sta+sys)d\sigma_{J/\psi}^{coh}/dy = 2.38^{+0.34}_{-0.24}(sta+sys) mb and dσJ/ψinc/dy=0.980.17+0.19(sta+sys)d\sigma_{J/\psi}^{inc}/dy = 0.98^{+0.19}_{-0.17}(sta+sys) mb, respectively. The results are compared to theoretical models for J/ψJ/\psi production and the coherent cross section is found to be in good agreement with those models which include nuclear gluon shadowing consistent with EPS09 parametrization. In addition the cross section for the process γγe+e\gamma\gamma \to e^+e^- has been measured and found to be in agreement with the STARLIGHT Monte Carlo predictions.publishedVersio

    Mid-rapidity anti-baryon to baryon ratios in pp collisions at s\sqrt{s} = 0.9, 2.76 and 7 TeV measured by ALICE

    Get PDF
    The ratios of yields of anti-baryons to baryons probes the mechanisms of baryon-number transport. Results for anti-proton/proton, anti-Λ/Λ\Lambda/\Lambda, anti-Ξ+/Ξ\Xi^{+}/\Xi^{-} and anti-Ω+/Ω\Omega^{+}/\Omega^{-} in pp collisions at s\sqrt{s} = 0.9, 2.76 and 7 TeV, measured with the ALICE detector at the LHC, are reported. Within the experimental uncertainties and ranges covered by our measurement, these ratios are independent of rapidity, transverse momentum and multiplicity for all measured energies. The results are compared to expectations from event generators, such as PYTHIA and HIJING/B, that are used to model the particle production in pp collisions. The energy dependence of anti-proton/proton, anti-Λ/Λ\Lambda/\Lambda, anti-Ξ+/Ξ\Xi^{+}/\Xi^{-} and anti-Ω+/Ω\Omega^{+}/\Omega^{-}, reaching values compatible with unity for s\sqrt{s} = 7 TeV, complement the earlier anti-proton/proton measurement of ALICE. These dependencies can be described by exchanges with the Regge-trajectory intercept of αJ\alpha_J ≈ 0.5, which are suppressed with increasing rapidity interval Δy\Delta y, Any significant contribution of an exchange not suppressed at large Δy\Delta y (reached at LHC energies) is disfavoured.publishedVersio

    Measurement of the Cross Section for Electromagnetic Dissociation with Neutron Emission in Pb-Pb Collisions at √sNN = 2.76 TeV

    Get PDF
    The first measurement of neutron emission in electromagnetic dissociation of 208Pb nuclei at the LHC is presented. The measurement is performed using the neutron Zero Degree Calorimeters of the ALICE experiment, which detect neutral particles close to beam rapidity. The measured cross sections of single and mutual electromagnetic dissociation of Pb nuclei at √sNN = 2.76 TeV with neutron emission are σ_single EMD = 187.2±0.2 (stat.) +13.8−12.0 (syst.) b and σ_mutual EMD = 6.2 ± 0.1 (stat.) ±0.4 (syst.) b respectively. The experimental results are compared to the predictions from a relativistic electromagnetic dissociation model.publishedVersio

    Centrality dependence of the pseudorapidity density distribution for charged particles in Pb-Pb collisions at sNN\sqrt{s_{NN}} = 2.76 TeV

    Get PDF
    We present the first wide-range measurement of the charged-particle pseudorapidity density distribution, for different centralities (the 0-5%, 5-10%, 10-20%, and 20-30% most central events) in Pb-Pb collisions at sNN\sqrt{s_{NN}} = 2.76 TeV at the LHC. The measurement is performed using the full coverage of the ALICE detectors, -5.0 < η\eta < 5.5, and employing a special analysis technique based on collisions arising from LHC ' satellite' bunches. We present the pseudorapidity density as a function of the number of participating nucleons as well as an extrapolation to the total number of produced charged particles NchN_{ch} = 17165 +/- 772 for the 0-5% most central collisions). From the measured d\)._{ch}\).d\).eta\) distribution we derive the rapidity density distribution, d\)._{ch}\).dy, under simple assumptions. The rapidity density distribution is found to be significantly wider than the predictions of the Landau model, which reproduce data well at RHIC energies. We assess the validity of longitudinal scaling by comparing to lower energy results from RHIC. Finally the mechanisms of the underlying particle production are discussed based on a comparison with various theoretical models.publishedVersio

    Long-range angular correlations on the near and away side in p&#8211;Pb collisions at

    Get PDF

    Underlying Event measurements in pp collisions at s=0.9 \sqrt {s} = 0.9 and 7 TeV with the ALICE experiment at the LHC

    Full text link

    J/Ψ production and nuclear effects in p-Pb collisions at √sNN=5.02 TeV

    Get PDF
    Inclusive J/ψ production has been studied with the ALICE detector in p-Pb collisions at the nucleon–nucleon center of mass energy √sNN = 5.02TeV at the CERN LHC. The measurement is performed in the center of mass rapidity domains 2.03 < ycms < 3.53 and −4.46 < ycms < −2.96, down to zero transverse momentum, studying the μ+μ− decay mode. In this paper, the J/ψ production cross section and the nuclear modification factor RpPb for the rapidities under study are presented. While at forward rapidity, corresponding to the proton direction, a suppression of the J/ψ yield with respect to binary-scaled pp collisions is observed, in the backward region no suppression is present. The ratio of the forward and backward yields is also measured differentially in rapidity and transverse momentum. Theoretical predictions based on nuclear shadowing, as well as on models including, in addition, a contribution from partonic energy loss, are in fair agreement with the experimental results
    corecore