First measurements of charged particle multiplicity in p-p collisions at the LHC with the ALICE experiment

Massimo Masera on behalf of the ALICE CollaborationUniversity of Torino and I.N.F.N. - Italy masera@to.infn.itALICE general results and upgrades

LISHEP 2011 - Workshop on LHC Present and Future 4,10 July 2011Outline09/07/2011The ALICE experimentPresent detector performance Results from 2010 Pb-Pb run: Global event features Two particle correlation and flow Hard processes: heavy flavours and J/yThe future: plans for an upgrade of the ALICE detectorsConclusions

2LISHEP 2011I had to make choices: Pb-Pb results: pp only as a baseline Justa a (personal) selection of the available results

Heavy Ions at the LHC09/07/201132010Targets / nucleon pairTeV2.765.5Initial luminositycm-2 s-1310251027Number of colliding bunches137592Bunch spacingns50099.8*m3.50.5Transverse normalized emittancem31.5Ions per bunch1.21087107

LISHEP 2011ALICE: A Large Ion Collider Experiment Indeed ALICE has been designed to be the general purpose Heavy Ion experiment at the LHCALICE has also a physics programme for pp collisions, that are used as a reference for Pb-PbPbPb run: from Nov, 7 2010 30 daysCollected statistics: 3.75 b-1 (30 M hadronic m.b. interactions)09/07/20114

ALICE numbets: 1200 members100 institues30 CountriesLISHEP 201109/07/2011PLC 20J. Schukraft

Complete since 2008: ITS, TPC, TOF, HMPID,FMD, T0, V0, ZDC, Muon arm, Acorde PMD , DAQ

Partial installation (2010): 4/10 EMCAL* (approved 2009)7/18 TRD* (approved 2002)3/5 PHOS ~ 60% HLT (High Level Trigger)

2011 10/10 EMCAL10/18 TRD

*upgrade to the original setupITSTPCTRDTOFEMCALPHOSHMPIDL3 MagnetDetector statusLISHEP 20115Detector PerformanceTrackingVertexingPID09/07/20116LISHEP 2011

Tracking09/07/2011LISHEP 20117Tracking capabilities in the central barrel are crucial for most of the physics topics addressed in Pb-Pb collisionsTracking detectors: Inner Tracking System (ITS), Time Projection Chamber (TPC) and Transition Radiation Detector (TRD)Algorithm based on Kalman filter, with seeding in the TPC. ITS is used as a standalone tracker with leftover pointsHermetic detectors: very high efficiency for |h|5 GeV/cCharm RAA: comparison with p09/07/2011LISHEP 201131

Suppression for charm not too different w.r.t. that for pionsD mesons seem to be less suppressed for pT RAA pions: Energy loss for gluon > energy loss for quarks (Casimir factor) Energy loss of massless partons > energy loss of heavy quarks (dead cone effect)Heavy Flavours from m and e09/07/2011LISHEP 201132

Semileptonic decays of HF contribute to the electron and muon yields(Inclusive electron spectra) (cocktail of known sources) is dominated by HF for pT>3-4 GeV/cMuon yield is suppressed by a factor of ~3 for pT>6 GeV/c, where is dominated by Beauty RAA for muons and electrons are compatible within the large electron signal systematic uncertainties09/07/2011LISHEP 201133

Comparison with modelsLittle shadowing at medium-high pT (as predicted by EPS09 for cold nuclear matter) suppression is a hot matter effectLow pT rise: pPb data needed to understand itRadiative Eloss (BDMPS-ASW) D & muon lie on the same curveRadiative+collisional (WHDG @ 2.76 TeV)Fair descriptionLight-cone wave function approach with dissociation (Vitev)OK for muons (beauty)

J/ RAA: pp reference09/07/2011LISHEP 201134 3 days of data taking @ 2.76 TeVSample: 20.2 nb-1 (13.3 nb-1 used for the present analysis @ 7 TeV )J/y yield extracted from a fit to the invariant mass spectrum (crystal ball shape for the signal + double exponential for the background)Good agreement of differential cross sections with pQCD

J/ RAA: results09/07/2011LISHEP 201135

Contribution from B feed-down:~ 10% from p-p measurement (LHCb Coll., arXiv:1103.0423)Rough estimation assuming simple scaling with Ncoll: ~ 11% reduction of RAA0-80%

Inclusive J/ RAA0-80% = 0.49 0.03 (stat.) 0.11 (sys.) Bars: statistical errorsOpen rectangles: systematic errors dependent on centrality Filled rectangle: common systematics Suppression of ~0.5 Cold Nuclear Matter Effects not measured pPb data needed for thisJ/ RAA: comparison with RHIC09/07/2011LISHEP 201136ALICE data plotted as a function of J/y less suppressed at LHC (2.5