1 / 17

First measurements in Pb—Pb collisions at  s NN =2.76 TeV with ALICE at the LHC

Rencontres de Moriond La Thuile , Aosta valley (Italy) March 20-27, 2011. First measurements in Pb—Pb collisions at  s NN =2.76 TeV with ALICE at the LHC. M. Nicassio ( University and INFN Bari) for the ALICE Collaboration. Contents. Introduction

cheri
Télécharger la présentation

First measurements in Pb—Pb collisions at  s NN =2.76 TeV with ALICE at the LHC

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Rencontres de Moriond La Thuile, Aosta valley (Italy) March 20-27, 2011 First measurements in Pb—Pbcollisions at sNN=2.76 TeV with ALICE at the LHC M. Nicassio (University and INFN Bari) for the ALICE Collaboration

  2. Contents • Introduction • ALICE experiment goal and apparatus • data takingconditions and eventselection • centralitydetermination • First measurements • multiplicity density ofprimarychargedparticles • Phys. Rev. Lett. 105, 252301 (2010), arXiv:1011.3916 • Phys. Rev. Lett. 106, 032301 (2011), arXiv:1012.1657 • elliptic flow ofprimarychargedparticles • Phys. Rev. Lett. 105, 252302 (2010), arXiv:1011.3914 • Bose—Einsteincorrelations • Phys. Lett .B 696 (2011) 328-337, arXiv:1012.4035 • ptspectraofprimarychargedparticles and RAA • Phys. Lett .B 696 (2011) 30-39, arXiv:1012.1004 • Summary and outlook SeeJochen talk Rencontres de Moriond - 23/03/2011

  3. The ALICE experiment • Main goal • study the propertiesofQuark—Gluon Plasma formed in • heavy-ioncollisions • Maindetectorsusedfor first analyses • InnerTrackingSystem • SiliconPixel Detector • r=3.9 cm |h|<2.0 innerlayer • r=7.6 cm |h|<1.4 outerlayer • 10M pixels,1200 read-out chips • TimeProjectionChamber • 85<r<247 cm, |h|<0.9 • V0scintillators • at 0.9 and 3.3 m on either side of IP • 2.8<|h|<5.1 and -3.7<|h|<-1.7 • Zero DegreeCalorimeters • at 114 m on either side of IP ITS V0C ZDC V0A TPC ZDC Rencontres de Moriond - 23/03/2011

  4. Trigger and eventselection • First runs with Pb ions @ sNN=2.76 TeV • 4 or 66 bunches • 1 to 7107 ions of 208Pb per bunch • 0.5 to 81023 cm-2s-1 estimated luminosity • interaction rate 50 Hz = 4Hz+45 Hz+1Hz • luminousregion: 5.9 cm in z, 50 mm in transverse direction • Triggeringwith SPD and both V0 arrays • two out ofthree trigger signals • two SPD pixel chips hit in the outerlayer • a signal in V0A • a signal in V0C • coincidencebetweenboth V0 arrays more efficient for • electromagnetic interaction suppression • Background removal • electromagneticinteractions: neutron ZDC minimal energydeposit • beam-background: V0 timing information, correlationbetween TPC • tracks andSPD hits Hadroniccollisions Electromagneticinteractions Beam-background Rencontres de Moriond - 23/03/2011

  5. Centralitydetermination • Twocomponentmodelofparticle production based on Glauberdescription • ofnuclearcollisions • Nancestors=fNpart+(1-f)Ncoll • particleproducedbyeach source describedby NBD • Assumption in Glaubermodelcalculation • Woods-Saxondistributionfornuclear density • r = 6.620.06 fm • skin depth a = 0.5460.010 fm • minimum inter-nucleon distance = 0.40.4 fm • interaction distance given by sinelNN = 645 mb at sNN=2.76 TeV • (frominterpolation of data) GlauberfitofV0 amplitudedistributionaboveananchorpoint correspondingto 88% of the hadroniccross-section, where trigger isfullyefficient and background negligible Rencontres de Moriond - 23/03/2011

  6. Centralitydetermination GlauberfitofV0 amplitudedistributionaboveananchorpoint correspondingto 88% of the hadroniccross-section, where trigger isfullyefficient and background negligible Rencontres de Moriond - 23/03/2011

  7. Results I: multiplicity density ofprimary chargedparticles • Energy dependence • Increase relative to RHIC and ppfactor 2 Analysis on 3600 events: - 5% mostcentral - |zvtx|<7 cm - primaryvertex and tracklets reconstructed in the SPD - TPC tracksas a cross check (dNch/dh)/(0.5<Npart>)= 8.3  0.4 (sys.) Rencontres de Moriond - 23/03/2011

  8. Results I: multiplicity density ofprimary chargedparticles • Centralitydependence Analysis on 49k events: -|zvtx|<7 cm - primaryvertex and tracklets reconstructed in the SPD - TPC tracksas a cross check • Same trend as at RHIC • Increasefrom peripheral to central •  factor 2 Rencontres de Moriond - 23/03/2011

  9. Results I: multiplicity density ofprimary chargedparticles • Comparisonwithmodels • two-componentmodels (pQCDprocesses + soft interactions) • saturationmodels Rencontres de Moriond - 23/03/2011

  10. Results II: elliptic flow ofprimary chargedparticles • Transversemomentumdependenceof v2 • No changes in v2(pt) • comparedto RHIC • ptdependece in centrality • classessimilarto RHIC • Analysis on 45k events: • centralityselectioncutting on TPC trackmultiplicity • - |zvtx|<10 cm • ITS and TPC tracks (TPC tracksas a cross check) • variousanalysistechniques Rencontres de Moriond - 23/03/2011

  11. Results II: elliptic flow ofprimary chargedparticles • Centralitydependenceofintegratedelliptic flow • Comparisonwith RHIC results30 % higher • Hydrodynamicmodelpredictionswithviscous • corrections in agreement withobservedincrease |h|<0.8 0.2<pt<5GeV/c Rencontres de Moriond - 23/03/2011

  12. Results II: elliptic flow ofprimary chargedparticles • Energy dependenceofintegratedelliptic flow • Increase in the magnitudeofelliptic flow withenergy 20-30% centralityclass Rencontres de Moriond - 23/03/2011

  13. Results III: two-pionBose—Einstein correlations • HBT radii and decouplingtimemultiplicitydependence • Volume ofhomogeneityregion: • lineardependence on dNch/dh, • twotimeslargerthan at RHIC • tf:lineardependence on • (dNch/dh)1/3, 1.4 times • largerthan at RHIC • Analysis on 16k events: • 5% mostcentralcollisions • - |zvtx|<12 cm • TPC tracks Rencontres de Moriond - 23/03/2011

  14. Results IV: ptspectraofprimary chargedparticles and RAA |h|<0.8 0.3<pt<20GeV/c Exponential • Analysis on 2.3M events: • - |zvtx|<10 cm • ITS+TPCtracks Powerlaw Peripheralevents and scaled ppreferencehavesame pt dependence • ppreference at 2.76 TeV: mainapproach • interpolationof ALICE measurements in ptbins (at 0.9 and 7TeV), • assuming a power law for the increase of the yield with s Rencontres de Moriond - 23/03/2011

  15. Results IV: ptspectraofprimary chargedparticles and RAA |h|<0.8 0.3<pt<20GeV/c • Alternativesfor • ppreference: • CDF data in • interpolation • NLO scalingof • pp data at 0.9 • TeV • In centralcollisions strong suppression • and clearchange in shape • In peripheralcollisions no ptdependence • above2GeV/c • Comparisonwith RHIC in centralcollisions: • strongersuppressionof high pt particles • very dense medium formed at LHC Rencontres de Moriond - 23/03/2011

  16. Summary and outlook • First ALICE measurements in PbPbcollisions • multiplicity a factor2higherthan at RHIC, samecentrality • dependence • elliptic flow 30% higherthan at RHIC • HBT radii and decouplingtimein centralcollisions • 10-35% and 30% higherthan at RHIC • Ongoingstudies and outlook • measurementsforidentifiedparticles • soft physicsstudies (resonances, baryons and strangeness) • hard physicsstudies (open heavy flavours, energy loss, jets) • lookingforward at PbPbcollisions at the end of 2011 • target forintegratedluminosityfactor3 (or more) higher • first injectionsofpA Rencontres de Moriond - 23/03/2011

  17. Rencontres de Moriond - 23/03/2011

More Related