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


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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

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

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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—Pbcollisions

at sNN=2.76 TeV with ALICE at the LHC

M. Nicassio (University and INFN Bari)

for the ALICE Collaboration


First measurements in pb pb collisions at s nn 2 76 tev with alice at the lhc

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


First measurements in pb pb collisions at s nn 2 76 tev with alice at the lhc

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


First measurements in pb pb collisions at s nn 2 76 tev with alice at the lhc

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


First measurements in pb pb collisions at s nn 2 76 tev with alice at the lhc

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


First measurements in pb pb collisions at s nn 2 76 tev with alice at the lhc

Centralitydetermination

GlauberfitofV0 amplitudedistributionaboveananchorpoint

correspondingto 88% of the hadroniccross-section, where trigger

isfullyefficient and background negligible

Rencontres de Moriond - 23/03/2011


First measurements in pb pb collisions at s nn 2 76 tev with alice at the lhc

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


First measurements in pb pb collisions at s nn 2 76 tev with alice at the lhc

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


First measurements in pb pb collisions at s nn 2 76 tev with alice at the lhc

Results I: multiplicity density ofprimary

chargedparticles

  • Comparisonwithmodels

    • two-componentmodels (pQCDprocesses + soft interactions)

    • saturationmodels

Rencontres de Moriond - 23/03/2011


First measurements in pb pb collisions at s nn 2 76 tev with alice at the lhc

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


First measurements in pb pb collisions at s nn 2 76 tev with alice at the lhc

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


    First measurements in pb pb collisions at s nn 2 76 tev with alice at the lhc

    Results II: elliptic flow ofprimary

    chargedparticles

    • Energy dependenceofintegratedelliptic flow

    • Increase in the magnitudeofelliptic flow withenergy

    20-30% centralityclass

    Rencontres de Moriond - 23/03/2011


    First measurements in pb pb collisions at s nn 2 76 tev with alice at the lhc

    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


    First measurements in pb pb collisions at s nn 2 76 tev with alice at the lhc

    Results IV: ptspectraofprimary

    chargedparticles and RAA

    |h|<0.80.3<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


    First measurements in pb pb collisions at s nn 2 76 tev with alice at the lhc

    Results IV: ptspectraofprimary

    chargedparticles and RAA

    |h|<0.80.3<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


    First measurements in pb pb collisions at s nn 2 76 tev with alice at the lhc

    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


    First measurements in pb pb collisions at s nn 2 76 tev with alice at the lhc

    Rencontres de Moriond - 23/03/2011


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