Physics with the ALICE experiment

ALICE experiment at LHC collects data in pp collisions at $\sqrt{s}$=0.9, 2.76 and 7 TeV and in PbPb collisions at 2.76 TeV. Highlights of the detector performance and an overview of experimental results measured with ALICE in pp and AA collisions are presented in this paper. Physics with proton-proton collisions is focused on hadron spectroscopy at low and moderate $p_T$. Measurements with lead-lead collisions are shown in comparison with those in pp collisions, and the properties of hot quark matter are discussed.Comment: Presented at the Conference of the Nuclear Physics Division of the Russian Academy of Science, 11-25.11.2011, ITEP, Moscow. 16 pages, 14 figure

Measurement of electrons from heavy-flavour decays in pp and Pb-Pb collisions with ALICE at the LHC

The ALICE experiment has measured at mid-rapidity electrons from heavy-flavour decays in pp collisions at $\sqrt{s}$ = 2.76 and 7 TeV, and in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV. In pp collisions, electrons from charm-hadron and from beauty-hadron decays are identified by applying cuts on displaced vertices. The relative yield of electrons from beauty-hadron decays to those from heavy-flavour decays is extracted using electron-hadron correlations. Results are compared to pQCD-based calculations. In Pb-Pb collisions, the $p_{\rm T}$ dependence of the nuclear modification factor of electrons from heavy-flavour decays is presented in two centrality classes. The status on the analysis of electrons from beauty-hadron decays is reported in Pb-Pb collisions, in view of the measurement of the corresponding nuclear modification factor.Comment: 4 page, 5 figures, proceedings for the fifth International Conference on Hard and Electromagnetic Probes of High Energy Nuclear Collisions (Hard Probes 2012), May 27 - June 1, Cagliari, Ital

Charged particle production in Pb--Pb collisions at the LHC with the ALICE detector

The ALICE collaboration measured charged particle production in $\sqrt{s_{NN}}=2.76$ TeV Pb--Pb collisions at the LHC. We report on results on charged particle multiplicity and transverse momentum spectra. All the results are presented as a function of the centrality of the collision, estimated with a Glauber Monte Carlo fit to multiplicity distributions reconstructed in various detectors. The applicability of the Glauber model at LHC energies, the precision of the centrality determination and the related systematic uncertainties are discussed in detail. Particles are tracked in the pseudorapidity window $|\eta| \lesssim 0.9$\ with the silicon Inner Tracking System (ITS) and the Time Projection Chamber (TPC), over the range 0.15 < \pt \lesssim 50 GeV/$c$. The low-$p_t$ cut-off is further reduced in the multiplicity measurement using "tracklets", reconstructed in the 2 innermost layers of the ITS. The charged particle multiplicity is measured in $|\eta| < 0.5$ to be $\mathrm{d}N_{ch}/\mathrm{d}\eta = 1601 \pm 60$ in 5% most central Pb--Pb collisions, indicating an energy density a factor $\sim 3$ higher than at RHIC. Its evolution with centrality shows a pattern strikingly similar to the one measured at RHIC. Intermediate (5 \lesssim \pt \lesssim 15 GeV/$c$) transverse momentum particles are found to be most strongly suppressed with respect to pp collisions, consistent with a large energy loss of hard-scattered partons in the hot and dense medium. The results are presented in terms of the nuclear modification factor $R_{\mathrm{AA}}$ and compared to theoretical expectations.Comment: 4 pages, 2 figures. Proceedings of the 5th international conference on Hard and Electromagnetic Probes of High Energy Nuclear Collisions. Updated version after referee report (minor changes

Measurement of heavy-flavour production in proton-proton collisions at sqrt{s} = 7 TeV with ALICE

The measurement of the heavy-flavour production cross sections in pp collisions at the LHC will allow to test perturbative QCD calculations in a new energy domain. Moreover, within the physics program of the ALICE experiment, it will provide the reference for the study of medium effects in Pb-Pb collisions, where heavy quarks are regarded as sensitive probes of parton-medium interaction dynamics. We present the status and first preliminary results of charm and beauty production measurements with the ALICE experiment, using hadronic D meson decays and semi-leptonic D and B meson decays, including the first cross section measurement of muons from heavy flavour decays at forward rapidity. We also describe the preliminary cross section measurement for J/psi production, obtained using the di-electron decay channel at central rapidity and the di-muon decay channel at forward rapidity.Comment: 8 pages, 5 figures, proceedings of the conference HARD PROBES 2010, Eilat, October 201

Pi0 and Eta measurement with photon conversions in ALICE in proton-proton collisions at sqrt(s) = 7 TeV

We present a measurement of the Pi0 transverse momentum spectrum and of the Eta/Pi0 ratio in proton-proton collisions at sqrt(s) = 7 TeV at the CERN LHC. In this analysis the reconstruction of Pi0 and Eta mesons has been done via photon conversions in the central tracking system of ALICE. Therefore, this method is completely independent from the electromagnetic calorimeters. It makes the Pi0 (Eta) measurement possible down to pt = 0.4 (0.6) GeV/c with a very good resolution and a very small background. For 100 Mio. pp collisions the pt reach is 7 GeV/c. The results are compared to NLO pQCD calculations.Comment: Proceedings to talk at HardProbes 2010, 4 page

Hadron Correlations Measured with ALICE

Angular particle correlations are a powerful tool to study collective effects and in-medium jet modification as well as their interplay in the hot and dense medium produced in central heavy-ion collisions. We present measurements of two-particle angular correlations of inclusive charged and identified particles performed with the ALICE detector. The near-side peak in the short-range correlation region is quantitatively analyzed: while the rms of the peak in $\phi$-direction is independent of centrality within uncertainties, we find a significant broadening in $\eta$-direction from peripheral to central collisions. The particle content of the near-side peak is studied finding that the $p/\pi$ ratio of particles associated to a trigger particle is much smaller than the one in the bulk of the particles and consistent with fragmentation of a parton in vacuum.Comment: Proceedings of plenary talk at the 5th international conference on hard and electromagnetic probes of high-energy nuclear collisions (Hard Probes 2012), Cagliari, Ital

High pt identified particle production in ALICE

The ALICE experiment is a dedicated heavy ion physics detector at the LHC with unique capabilities for studying identified particle production. In this proceeding preliminary results for RAA for pi and K+p (sum), are reported, based on measurements in pp at sqrt(s) = 2.76 TeV and Pb-Pb at sqrt(sNN) = 2.76 TeV. The results are compared to theoretical predictions and measurements at RHIC.Comment: 7 pages, 6 figures, proceedings from 5th International Conference on Hard and Electromagnetic Probes of High-Energy Nuclear Collisions (Hard Probes 2012) at Cagliari (Italia

Measurement of heavy-flavour decay muon production at forward rapidity in pp and Pb-Pb collisions at sqrt(s_NN)=2.76 TeV with the ALICE experiment

The ALICE experiment measured the heavy-flavour production in the semi-muonic decay channel at forward rapidities ($2.5<y<4$) in pp and Pb--Pb collisions at $\sqrt{s_{{NN}}} = 2.76$ TeV. We report on the first results on the $p_{\rm T}$-differential cross-sections in pp collisions as well as on the nuclear modification factors as a function of the transverse momentum and centrality.Comment: 4 pages, 3 figures, Proceedings of parallel talk at the 5th international conference on hard and electromagnetic probes of high-energy nuclear collisions (Hard Probes 2012), Cagliari, Ital

Production of Neutral Pions and Eta-mesons in pp Collisions Measured with ALICE

Invariant cross sections for neutral pions and eta mesons in pp collisions at sqrt(s) = 0.9, 2.76, and 7 TeV were measured by the ALICE detector at the Large Hadron Collider. Next-to-leading order (NLO) perturbative QCD calculations describe the pi0 and eta spectra at 0.9 TeV, but overestimate the measured cross sections at 2.76 TeV and 7 TeV. The measured eta/pi0 ratio is consistent with mT scaling at 2.76 TeV. At 7 TeV indications for a violation of mT scaling were found.Comment: 4 pages, 2 figures, to appear in the proceedings of the XXII International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions, Quark Matter 2011, Annec

Multi-strange baryon elliptic flow in Pb-Pb collisions at \sqrt{s_{NN}} = 2.76 TeV measured with the ALICE detector

We present the results on elliptic flow with multi-strange baryons produced in Pb-Pb collisions at \sqrt{s_{NN}} = 2.76 TeV. The analysis is performed with the ALICE detector at LHC. Multi-strange baryons are reconstructed via their decay topologies and the v_2 values are analyzed with the two-particle scalar product method. The p_T differential v_2 values are compared to the VISH2+1 model calculation and to the STAR measurements at 200 GeV in Au+Au collisions. We found that the model describes \Xi and \Omega v_2 measurements within experimental uncertainties. The differential flow of \Xi and \Omega is similar to the STAR measurements at 200 GeV in Au+Au collisions.Comment: Prepared for the Proceedings of the International Conference on "Critical Point and Onset of Deconfinement - CPOD 2011", Wuhan, November 7-11, 201