First results with heavy-ion collisions at the LHC with ALICE

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1 First results with heavy-ion collisions at the LHC with ALICE Domenico Elia INFN, Bari (Italy) on behalf of the ALICE Collaboration D. Elia (INFN Bari, Italy) PANIC 011 / Boston, MA (USA) July 4-9, 011 1

2 Contents Heavy-ion physics at ALICE: experimental apparatus data taking and event selection centrality determination First results: charged-particle multiplicity strange and identified hadrons charged-particle elliptic flow Bose-Einstein correlations charged-particle high-p T and R AA Already published analyses: Phys. Rev. Lett. 5 (0) 5301 Phys. Rev. Lett. 6 (011) Phys. Rev. Lett. 5 (0) 530 Phys. Lett. B 696 (011) 38 Phys. Lett. B 696 (011) 30 Conclusions and perspectives D. Elia (INFN Bari, Italy) PANIC 011 / Boston, MA (USA) July 4-9, 011

3 Contents Heavy-ion physics at ALICE: experimental apparatus data taking and event selection centrality determination First results: charged-particle multiplicity strange and identified hadrons charged-particle elliptic flow Bose-Einstein correlations charged-particle high-p T and R AA PANIC11, see also: H. Pereira Quarkonium, Monday, p. 1L Z. Conesa del Valle Open heavy flavour, Tuesday, p. 3L J. Thomas Charge asymmetry, Thursday, p. 4K C. Klein-Boesing Jet properties, Thursday, p. 5K Conclusions and perspectives D. Elia (INFN Bari, Italy) PANIC 011 / Boston, MA (USA) July 4-9, 011 3

4 ALICE experiment at LHC A Large Ion Collider Experiment: general-purpose experiment at LHC designed for heavy-ions ultimate goal is the study of Quark Gluon Plasma properties very rich heavy-ion physics programme: from global event characterization (multiplicity, η distributions ) to properties of the system created in the collision (hadrochemistry, temperature, energy density, HBT, flow, jets ) D. Elia (INFN Bari, Italy) PANIC 011 / Boston, MA (USA) July 4-9, 011 4

5 ALICE experiment at LHC A Large Ion Collider Experiment: general-purpose experiment at LHC designed for heavy-ions ultimate goal is the study of Quark Gluon Plasma properties very rich heavy-ion physics programme: from global event characterization (multiplicity, η distributions ) to properties of the system created in the collision (hadrochemistry, temperature, energy density, HBT, flow, jets ) Main design features: precise and robust tracking over a broad p T range low momentum cut-off (p T <0 MeV/c) excellent Particle IDentification dielectrons (barrel) and dimuons (dedicated spectrometer) direct photons (high-resolution calorimeter) D. Elia (INFN Bari, Italy) PANIC 011 / Boston, MA (USA) July 4-9, 011 5

partial capabilities (% in 011): TRD (60%), PHOS (60%), EMCAL (0%)

6 Experimental apparatus Hadron & µ capabilities complete since 008: ITS, TPC, TOF, HMPID, MUONS, V0, T0, ZDC, ACORDE, TRIGGER EM (e & γ) partial capabilities (% in 011): TRD (60%), PHOS (60%), EMCAL (0%) ITS D. Elia (INFN Bari, Italy) PANIC 011 / Boston, MA (USA) July 4-9, 011 6

7 Data taking summary Year of Data Taking Collision System Energy N. of Events, trigger 009 pp 900 GeV 300 K, MB 009 pp.36 TeV ~ 40 K, MB 0 pp 900 GeV ~ 8 M, MB 0 pp 7 TeV ~ 800 M, MB ~ 0 M, µ trigger ~ 0 M, high mult. 0 PbPb.76 TeV/NN ~ 30 M, MB 011 pp.76 TeV ~ 70 M, MB > 5 M, µ trigger ~ M, high mult. pp increased L by 4 in 0 (L peak ~ 1.x 30, L int < ~ nb -1 ) PbPb delivered L int > 7 µb -1 Pb in 4 weeks (L peak > x 5, ~ 1/0 L max ) D. Elia (INFN Bari, Italy) PANIC 011 / Boston, MA (USA) July 4-9, 011 7

8 ALICE pp physics results Published papers N ch multiplicities & distributions 0.9 TeV: EPJC Vol. 65 (0) /.36 TeV: EPJC Vol. 68 (0) 89 _ 7 TeV: EPJC Vol. 68 (0) 345 p /p ratio (0.9 & 7 TeV) PRL Vol. 5 (0) 0700 Momentum distributions (0.9 TeV) PLB Vol. 693 (0) 53 Strange particle production (0.9 TeV) EPJC Vol. 71, (011) 1594 Identified particle spectra (0.9 TeV) EPJC Vol. 71, (011) 1655 Bose-Einstein correlations 0.9 TeV: PRD Vol. 8 (0) / 7.0 TeV: arxiv: to PRD J/ψ production (7 TeV) arxiv: [hep-ex] to PLB Ongoing: strangeness (K 0,Λ,Ξ,Ω,φ), heavy-flavor (charm D 0,D +, D*) analysis of HI comparison data TeV) D. Elia (INFN Bari, Italy) PANIC 011 / Boston, MA (USA) July 4-9, 011 8

Data taking with PbPb First heavy-ions @ snn =.

9 Data taking with PbPb First snn =.76 TeV in LHC: one month at the end of 0 about 30 M nuclear interaction MB triggers collected D. Elia (INFN Bari, Italy) PANIC 011 / Boston, MA (USA) July 4-9, 011 9

10 Data taking with PbPb First s NN =.76 TeV in LHC: one month at the end of 0 about 30 M nuclear interaction MB triggers collected Running conditions (data for first results): 4 or 66 bunches per beam 1 to 7 x 7 ions of 08 Pb per bunch 0.5 to 8 x 3 cm - s -1 estimated luminosity 50 Hz interaction rate: 4 Hz hadronic collisions 45 Hz electromagnetic interactions 1 Hz beam-background luminous region: σ = 5.9 cm (beam direction) σ = 50 µm (transverse direction) D. Elia (INFN Bari, Italy) PANIC 011 / Boston, MA (USA) July 4-9, 011

11 Trigger and event selection Trigger based on SPD and both V0 arrays: two trigger signals out of: two SPD pixel chips hit in the outer layer ( η < 1.4 ) a signal in V0A (.8 < η < 5.1 ) a signal in V0C ( -3.7 < η < -1.7 ) tighter condition in later runs: coincidence between both V0 arrays (i.e. 3 out of 3 trigger signals) more efficient suppression of electromagnetic interactions D. Elia (INFN Bari, Italy) PANIC 011 / Boston, MA (USA) July 4-9,

12 Trigger and event selection Trigger based on SPD and both V0 arrays: two trigger signals out of: two SPD pixel chips hit in the outer layer ( η < 1.4 ) a signal in V0A (.8 < η < 5.1 ) a signal in V0C ( -3.7 < η < -1.7 ) tighter condition in later runs: coincidence between both V0 arrays (i.e. 3 out of 3 trigger signals) more efficient suppression of electromagnetic interactions Background removal: electromagnetic interactions: neutron ZDC minimal energy deposit beam-background: correlation between TPC tracks and SPD hits D. Elia (INFN Bari, Italy) PANIC 011 / Boston, MA (USA) July 4-9, 011 1

13 Centrality determination Based on V0 amplitude distribution: fitted according to the Glauber model supposing N sources = f N part + (1 f) N coll each source emits particles according to a NBD further assumptions in the Glauber model calculation Wood-Saxon distribution for the nuclear density interaction distance given by σ inel NN = 64 ± 5 mb at s NN =.76 TeV (from interpolation of data) D. Elia (INFN Bari, Italy) PANIC 011 / Boston, MA (USA) July 4-9,

14 Centrality determination Based on V0 amplitude distribution: fitted according to the Glauber model supposing N sources = f N part + (1 f) N coll Events % 40-50% Data Glauber fit 30-40% 0-30% -0% VZERO Amplitude (a.u.) % 70-80% 0-5% 60-70% f 0.8 derive N part and N coll little dependence on the centrality estimator (ZDC, tracks, ZDC vs V0...) Fitted above an anchor point (150) corresponding to 88% of the hadronic cross-section, where trigger is fully efficient and background negligible D. Elia (INFN Bari, Italy) PANIC 011 / Boston, MA (USA) July 4-9,

15 Charged-particle multiplicity Energy dependence of charged-particle production: 1600 charged particles per unit rapidity at mid-rapidity in central collisions s NN =.76 TeV, 0-5% most central, η <0.5!) part (dn ch /d#)/(0.5"n PbPb(0-5 %) ALICE PbPb(0-5 %) NA50 AuAu(0-5 %) BRAHMS AuAu(0-5 %) PHENIX AuAu(0-5 %) STAR AuAu(0-6 %) PHOBOS Multiplicities RHIC pp NSD ALICE pp NSD CMS pp NSD CDF pp NSD UA5 pp NSD UA1 pp NSD STAR AA 0.15 $ s NN pp(pp) 0.11 $ s NN LHC 0 PRL 5, 5301 (0) 3 s NN (GeV) D. Elia (INFN Bari, Italy) PANIC 011 / Boston, MA (USA) July 4-9,

16 Charged-particle multiplicity Energy dependence of charged-particle production: 1600 charged particles per unit rapidity at mid-rapidity in central collisions!) part (dn ch /d#)/(0.5"n s NN =.76 TeV, 0-5% most central, η < PbPb(0-5 %) ALICE PbPb(0-5 %) NA50 AuAu(0-5 %) BRAHMS AuAu(0-5 %) PHENIX AuAu(0-5 %) STAR AuAu(0-6 %) PHOBOS Multiplicities RHIC pp NSD ALICE pp NSD CMS pp NSD CDF pp NSD UA5 pp NSD UA1 pp NSD STAR AA pp(pp) 0.11 $ s NN LHC 0.15 $ s NN highest ever achieved higher than most theoretical predictions 1.9 x TeV. x RHIC energy density: ε(τ 0 ) LHC 3 x ε(τ 0 ) RHIC 0 PRL 5, 5301 (0) 3 s NN (GeV) (assuming τ 0 to be the same at RHIC and LHC) D. Elia (INFN Bari, Italy) PANIC 011 / Boston, MA (USA) July 4-9,

17 Charged-particle multiplicity Centrality dependence: =.76 TeV 8 Multiplicities 4 = 0. TeV s NN!/) 6 3 s NN!/) part N 4 part N (dn ch /d#)/(" Pb-Pb.76 TeV ALICE pp NSD.76 TeV pp Inel.76 TeV Au-Au 0. TeV interpolation of.36 and 7 TeV data 1 (dn ch /d#)/(" " N! part same trend at LHC and RHIC x increase from peripheral to central D. Elia (INFN Bari, Italy) PANIC 011 / Boston, MA (USA) July 4-9,

18 Charged-particle multiplicity Centrality dependence: Model comparison =.76 TeV 8 Multiplicities 4 = 0. TeV s NN!/) 6 3 s NN!/) part N 4 part N (dn ch /d#)/(" Pb-Pb.76 TeV ALICE pp NSD.76 TeV pp Inel.76 TeV Au-Au 0. TeV interpolation of.36 and 7 TeV data 1 (dn ch /d#)/(" " N! part same trend at LHC and RHIC x increase from peripheral to central DPMJET (with string fusion) HIJING (no quenching) Saturation models models with moderation of particle production with centrality favoured by data (also at RHIC) D. Elia (INFN Bari, Italy) PANIC 011 / Boston, MA (USA) July 4-9,

19 Identified particle spectra Comparison with RHIC: significant change in slope most dramatic for protons LHC D. Elia (INFN Bari, Italy) PANIC 011 / Boston, MA (USA) July 4-9,

20 Identified particle spectra Comparison with RHIC: significant change in slope most dramatic for protons Quantified by Blast Wave: LHC LHC RHIC Hydro parameters from Blast Wave fits very strong radial flow, β 0.66 stronger than predicted by most recent hydro D. Elia (INFN Bari, Italy) PANIC 011 / Boston, MA (USA) July 4-9, 011 0

21 Baryon anomaly: Λ / K 0 Baryon/meson ratio strongly enhanced: increasing with centrality x 3 wrt pp value still present at 6 GeV/c x 3 Ratio at maximum slightly larger at LHC than at RHIC maximum shift very little in p T, despite significant differences in spectra D. Elia (INFN Bari, Italy) PANIC 011 / Boston, MA (USA) July 4-9, 011 1

22 Elliptic flow Energy dependence: v % centrality class v n = cos(n[" #$ n ]) dn d(" #$ n ) %1+ & v n cos(n[" #$ n ]) n= PRL 5, 530 (0) 3 ALICE STAR PHOBOS PHENIX NA49 CERES E877 EOS E895 FOPI s NN 4 (GeV) D. Elia (INFN Bari, Italy) PANIC 011 / Boston, MA (USA) July 4-9, 011

23 Elliptic flow Energy dependence: v % centrality class v n = cos(n[" #$ n ]) dn d(" #$ n ) %1+ & v n cos(n[" #$ n ]) n= PRL 5, 530 (0) 3 ALICE STAR PHOBOS PHENIX NA49 CERES E877 EOS E895 FOPI s NN 4 (GeV) increase in v wrt RHIC (30%) described by hydro models (see e.g. [1]) with: - Glauber geometry - viscous correction η/s still small ( ) - changes expected in space-time evolution [1] H. Matsui etc al., Nucl. Phys. A830, 463C (009) D. Elia (INFN Bari, Italy) PANIC 011 / Boston, MA (USA) July 4-9, 011 3

Elliptic flow Centrality and p T dependence: v 0.1 0.1 0.08 0.06 0.04 0.

24 Elliptic flow Centrality and p T dependence: v v {} v {} (same charge) v {4} v {4} (same charge) v {q-dist} v {LYZ} v {EP} STAR v {LYZ} STAR centrality percentile and multi-particle methods differ as expected multi-particle estimates agree within errors as expected for collective flow very little change in v vs p T from 0. TeV (STAR) to.76 TeV (ALICE) same for three different centralities (consistent with hydro) D. Elia (INFN Bari, Italy) PANIC 011 / Boston, MA (USA) July 4-9, 011 4

25 Bose-Einstein correlations Assess space-time extension of the system: linear dependence on dn ch /dη ) 3 R out R side R long (fm Homogeneity volume (central collisions) E895.7, 3.3, 3.8, 4.3 GeV NA49 8.7, 1.5, 17.3 GeV CERES 17.3 GeV STAR 6.4, 00 GeV PHOBOS 6.4, 00 GeV ALICE 760 GeV RHIC LHC (fm/c) $ f Decoupling time (central collisions) E895.7, 3.3, 3.8, 4.3 GeV NA49 8.7, 1.5, 17.3 GeV CERES 17.3 GeV STAR 6.4, 00 GeV PHOBOS 6.4, 00 GeV ALICE 760 GeV RHIC LHC #dn /d"! ch PL B 696, 38 (011) /3 #dn /d"! ch D. Elia (INFN Bari, Italy) PANIC 011 / Boston, MA (USA) July 4-9, 011 5

26 Bose-Einstein correlations Assess space-time extension of the system: linear dependence on dn ch /dη ) 3 R out R side R long (fm Homogeneity volume (central collisions) E895.7, 3.3, 3.8, 4.3 GeV NA49 8.7, 1.5, 17.3 GeV CERES 17.3 GeV STAR 6.4, 00 GeV PHOBOS 6.4, 00 GeV ALICE 760 GeV RHIC LHC (fm/c) $ f Decoupling time (central collisions) E895.7, 3.3, 3.8, 4.3 GeV NA49 8.7, 1.5, 17.3 GeV CERES 17.3 GeV STAR 6.4, 00 GeV PHOBOS 6.4, 00 GeV ALICE 760 GeV RHIC LHC #dn /d"! ch PL B 696, 38 (011) Volume at decoupling: V LHC 300 fm 3 x V RHIC /3 #dn /d"! ch Lifetime (from collision to freeze-out): τ f LHC -11 fm/c 1.4 x τ f RHIC D. Elia (INFN Bari, Italy) PANIC 011 / Boston, MA (USA) July 4-9, 011 6

27 Charged-particle p T spectra Charged-particle nuclear modification factor (R AA ): PbPb, s NN =.76 TeV, η < 0.8, 0.3 < p T < 0 GeV/c - ) (GeV/c) N ch ) / (d! dp ) (d T T p 1/(" 1/N evt Pb-Pb scaled pp reference 0-5% 70-80% =.76 TeV s NN PbPb significantly below scaled pp for central collisions pp reference from interpolation of 0.9 and 7 TeV pp data in p T bins assuming the increase of the yield with s follows a power-law Central events: exponential shape below 5 GeV/c (GeV/c) PL B 696, 30 (011) p T Peripheral events: power-law shape at p T > 3 GeV/c similar to the pp reference D. Elia (INFN Bari, Italy) PANIC 011 / Boston, MA (USA) July 4-9, 011 7

28 Charged-particle p T spectra - ) (GeV/c) N ch ) / (d! dp ) (d T T p 1/(" 1/N evt Charged-particle nuclear modification factor (R AA ): PbPb, s NN =.76 TeV, η < 0.8, 0.3 < p T < 0 GeV/c Pb-Pb scaled pp reference 0-5% 70-80% =.76 TeV s NN PbPb significantly below scaled pp for central collisions R AA 1 0-5% 70-80% Pb-Pb =.76 TeV s NN Peripheral: no p T dependence for peripheral at p T > GeV/c Central: clear increase at higher p T to be understood minimum at 6-7 GeV/c R AA (GeV/c) PL B 696, 30 (011) p T (GeV/c) p T strong parton energy loss D. Elia (INFN Bari, Italy) PANIC 011 / Boston, MA (USA) July 4-9, 011 8

29 Charged-particle p T spectra Charged-particle nuclear modification factor (R AA ): PbPb, s NN =.76 TeV, η < 0.8, 0.3 < p T < 0 GeV/c R AA ALICE Pb-Pb s NN =.76 TeV (0-5%) STAR Au-Au s NN = 00 GeV (0-5%) PHENIX Au-Au s NN = 00 GeV (0 - %) (GeV/c) p T Comparison with RHIC: similar values at p T 1 GeV/c shape and maximum position similar at low-intermediate p T high p T (6-7 GeV/c): R AA (LHC) > R AA (RHIC) more energy loss, denser medium at LHC! D. Elia (INFN Bari, Italy) PANIC 011 / Boston, MA (USA) July 4-9, 011 9

30 Summary and outlook First ALICE measurements with heavy-ions: charged-particle multiplicity: factor larger than at RHIC, same centrality behaviour estimated energy density 3 x RHIC strange and identified hadrons: baryon anomaly still exists at LHC (similar than at RHIC) stronger radial flow (β 0.66) charged-particle elliptic flow: increasing v from RHIC to LHC, same centrality and p T dependence hadrons close to hydro limit (η/s 0.) space-time evolution of the PbPb collision (HBT): very large volume and lifetime at LHC (x and x 1.4 wrt RHIC) charged-particle nuclear modification factor R AA : high-p T suppression stronger than at RHIC D. Elia (INFN Bari, Italy) PANIC 011 / Boston, MA (USA) July 4-9,

31 Summary and outlook First ALICE measurements with heavy-ions: charged-particle multiplicity strange and identified hadrons charged-particle elliptic flow space-time evolution of the PbPb collision (HBT) charged-particle nuclear modification factor R AA Just a fraction of the available results shown: both due to time limits and personal preferences indeed many more analyses ongoing: from measurements for identified particles (spectra, ratios, flow) more on elliptic flow (large p T, higher-order armonics v n ) resonances, baryons and strangeness, HBT vs centrality hard probes: open heavy-flavour, quarkonia, energy loss, jets D. Elia (INFN Bari, Italy) PANIC 011 / Boston, MA (USA) July 4-9,

32 Future perspectives A lot of work (and exciting physics) ahead: we have had only 4 weeks in a year programme! rare signals need a factor 0 in integrated luminosity: expected to approach design luminosity this year ( x 0 wrt 0) quarkonia (J/ψ, Ψ, Y, Y ), heavy flavour (b,c), γ-jets, running at full LHC energy: -15% gain in energy density, larger cross section for rare probes running p-a for comparison data: distinguish QGP effects from nuclear effects ( shadowing ) study Color Glass Condensate running lower mass ions (Ar-Ar?): study volume effects much higher luminosity can be achieved D. Elia (INFN Bari, Italy) PANIC 011 / Boston, MA (USA) July 4-9, 011 3

33 Future perspectives A lot of work (and exciting physics) ahead: we have had only 4 weeks in a year programme! rare signals need a factor 0 in integrated luminosity: expected to approach design luminosity this year ( x 0 wrt 0) quarkonia (J/ψ, Ψ, Y, Y ), heavy flavour (b,c), γ-jets, running at full LHC energy: -15% gain in energy density, larger cross section for rare probes running p-a for comparison data: distinguish QGP effects from nuclear effects ( shadowing ) study Color Glass Condensate running lower mass ions (Ar-Ar?): study volume effects much higher luminosity can be achieved The Wonderland has just started! D. Elia (INFN Bari, Italy) PANIC 011 / Boston, MA (USA) July 4-9,

Heavy Ion Results from the ALICE Experiment

Heavy Ion Results from the ALICE Experiment Johannes P. Wessels on behalf of the ALICE Collaboration Institute for uclear Physics University of Münster D-89 Münster, Germany and CER, CH- Geneva, Switzerland