Roberta Arnaldi INFN, Torino for the ALICE Collaboration. Quarkonia in deconfined matter Acitrezza, September 28 th -30 th

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1 Roberta Arnaldi INFN, Torino for the ALICE Collaboration Quarkonia in deconfined matter Acitrezza, September 28 th -30 th

2 Physics motivations J/ψ measurement in PbPb 2.76 TeV with ALICE R AA and R CP results Comparison with results from other experiments Comparison with models Prospects: J/ψ production in ultra-peripheral collisions J/ψ flow 2

3 Physics motivations Quarkonium suppression is considered since a long time as one of the most striking signatures for QGP formation in AA collisions Sequential suppression of quarkonium states thermometer for the temperature reached in heavy ion collisions but many effects complicate the picture: cold nuclear matter (cc break-up,shadowing) cc recombination 3

4 Towards LHC results After SPS and RHIC J/ψ results many questions are still open RHIC: stronger suppression at forward rapidities SPS vs. RHIC: not clear trend of the suppression pattern versus energy LHC results can shed some light, investigating the role of the large charm quark multiplicity other quarkonia states (bottomonium) (almost unexplored in HI collisions: STAR ~200ϒ(1S+2S+3S) in 4

5 First LHC PbPb run The first LHC heavy ion run took place in November 2010 PbPb collisions at s=2.76 TeV Peak luminosity increasing from 3x10 23 to 3x10 25 Hz/cm 2 Similar integrated luminosity for ALICE, ATLAS, CMS ~9 μb -1 5

6 Quarkonium measurement in ALICE Quarkonium in ALICE can be measured in two ways: Central Barrel J/ψ e + e - ( y <0.9) Electrons tracked using ITS and TPC Particle identification: TPC (+TOF) Forward muon arm J/ψ μ + μ - (2.5<y<4) Muons identified and tracked in the muon spectrometer Acceptance coverage in both y regions down to zero p T ALICE results refer to inclusive J/ψ production e e µ - µ + 6

7 Pb-Pb collisions at s=2.76tev Trigger: Minimum bias trigger (V0A and V0C and SPD) ~ MB events collected Event selection: Rejection of beam gas events (V0 timing) Negligible EM background in the centrality range (0-80%) Integrated luminosity ~ 2.7 μb -1 Centrality: Estimate based on a Glauber model fit of the V0 amplitude Statistics imposes rather wide centrality bins for J/ψ analysis: J/ψ μ + μ - :0-10,10-20,20-40,40-80% J/ψ e + e - : 0-40, 40-80% 7

8 J/ψ e + e - at mid-rapidity Electrons tracking: ITS and TPC Particle identification: TPC (on-going PID with TRD and TOF) Cuts: η e+e- < % 40-80% Visible J/ψ signal, in spite of the low S/B (~ ) 8

9 J/ψ μ + μ - at forward rapidity Event/Track selection: to improve the purity of the muon sample, both muons reconstructed in the tracking and trigger chambers should satisfy the trigger algorithm reduction of hadronic background and fake tracks cut on the track position at the end of the front absorber 2.5 < y J/ψ < 4, 2.5<η μ <4, p T J/ψ >0 GeV/c No identification of J/ψ from B decays scattering in the absorber spoils the muon vertex information 9

10 Signal extraction J/ψ yield extracted from a fit (2-5 GeV/c 2 ) to the invariant mass spectrum assuming Crystal Ball shape for the signal (tails fixed to pp data, pure MC, MC signal embedded into real events) sum of two exponentials for the background ψ(2s) negligible with this statistics S/B centrality dependent (~ ), but good significance also in most central bin 10

11 Alternative signal extraction Mixed event technique also used to estimate the background mixed pair invariant mass distribution normalized to data in (1.5, 2.5) GeV/c 2 fit the background subtracted mass distribution with a Crystal Ball function and a straight line (or exponential) to account for a small residual background Results obtained with different techniques combined to extract <N J/ψ > and to evaluate systematic uncertainties 11

12 Centrality dependence of J/ψ parameters The increase of detectors occupancy with centrality may worsen the reconstruction resolution, affecting the J/ψ shape centrality dependence of J/ψ parameters is studied embedding a MC J/ψ into a real event No centrality dependence of J/ψ width and Crystal Ball parameters 12

13 Two approaches: Standard Monte-Carlo: Acceptance x efficiency J/ψ y and p T distributions interpolated from Phenix, CDF and LHC data A x eff = ± 0.04 (stat)% MC J/ψ embedded in real event allows the study of the A x eff centrality dependence small decreasing (~5%) of the reconstruction efficiency when increasing centrality 13

14 R AA Nuclear modification factor in each centrality R i = AA i incl bin TAA σ J ψ ( pp@ 2.76TeV ) with: Y Y i J ψ i i = J ψ J ψ BR N + i ( J ψ l l ) ( A ε ) N pp reference: measured J/ψ production cross section in pp@ s=2.76 TeV (3 days data taking in March 2011 see talk G. Bruno) incl σ J ψ ( 2.76TeV ) = 3.46 ± 0.13( stat) ± 0.32( syst) ± 0.28( syst. lumi) μb MB R CP R i CP = Y Y i J ψ T T i AA 40 80% 40 80% J ψ AA peripheral reference: Warning: 40-80% centrality bin not really peripheral 14

15 Systematic uncertainties sources centrality 0-10% 10-20% 20-40% 40-80% correlated N J/ψ 19 % 14 % 17% 14% - N J/ψ /N 40-80% J/ψ 12% 8% 7% - - Acc. inputs % Trigger eff % Tracking eff. 4% 2% 1% 0% 5% Reco eff % Branching ratio % Cross Section % <T AA > 4% 4% 4% 6% - <T AA > i /<T AA > 40-80% 6% 5% 4% - - Total for R AA 20% 15% 17% 15% 15% Total for R CP 14% 10% 8%

16 R AA vs. centrality Inclusive J/ψ R AA 0-80% = 0.49 ± 0.03 (stat.) ± 0.11 (syst.) Suppression with no strong centrality dependence Error bars: Statistical uncertainties Empty boxes: Centrality-dependent systematic uncertainties Blue box: common systematic uncertainties Contribution from B feed-down: ~ 10% from pp measurement (LHCb Coll., arxiv: ) Rough estimation assuming simple N coll scaling : ~11% reduction of R 0-80% AA 16

17 Comparison with PHENIX J/ψ R AA is larger with respect to PHENIX results at forward y Difference increases with centrality J/ψ R AA is compatible with RHIC mid-rapidity result, except for the most central collisions but CNM effects may be different at the two energies R AA 1.4 ALICE (Pb-Pb s = 2.76 TeV), 2.5<y<4, p >0 (preliminary) NN T PHENIX (Au-Au s NN = 0.2 TeV), 1.2< y <2.2, p >0 (arxiv: ) 1.2 PHENIX (Au-Au s NN = 0.2 TeV), y <0.35, p >0 (nucl-ex/ ) T T (*) ALICE <N part > is weighted by N coll <N part *> 17 Large ALICE centrality bins the <N part > values have been weighted by N coll

18 Comparison with CMS results ALICE R AA is significantly higher than the CMS result, but the covered kinematical region (y and p T ) is different CMS PAS HIN

19 Nuclear shadowing R AA R. Vogt, Phys.Rev.C81:044903, 2010 ALICE (Pb-Pb EPS09 (R. Vogt, priv. comm.) s NN = 2.76 TeV), 2.5<y<4, p >0 (preliminary) T JP. Lansberg, QM % 20-40% 10-20% 0-10% centrality Let s consider shadowing as the only CNM effect (cc break-up cross section expected to be negligible at LHC energies) Different approaches (J/ψ production through 2 1 or 2 2 partonic processes) and several npdf adopted Important shadowing contribution, but npdf are affected by large uncertainties LHC (end 2012?) 19

20 Comparison to models Statistical hadronization: P. Braun-Muzinger, J. Stachel, PLB490 (2000) 196 Andronic et al.,plb571(2003)36 Screening by QGP of all direct J/ψ CNM (shadowing) on open charm Charmonium production at phase boundary by statistical combination of uncorrelated charm quarks 20

21 Comparison to models Parton transport models: R.Rapp, X. Zhao, NPA 859, 114(2011) R.Rapp, X. Zhao, PRC (2010) X.Zhu, P.Zhuang,N.Xu,PLB607(2005)107 L.Yan,P.Zhuang,N.Xu,PRL97(2006) Y.Liu,Z.Qu,N.Xu,P.Zhuang,PLB678(2009)72 P.Zhuang, WE-Heraeus Seminar 2011 Prediction including: Prompt J/ψ dissociation in QGP J/ψ regeneration by charm quark pair recombination Feed-down from B decays Shadowing Shadowing and Cronin effect Prompt J/ψ dissociation in QGP J/ψ regeneration by charm quark pair recombination Feed-down contribution from B 21

22 R CP R CP is normalized to the centrality bin 40-80% Error bars: Statistical uncertainties Empty boxes: Centrality-dependent systematic uncertainties Statistical uncertainty of the reference bin propagated to the ratio Non centrality-dependent uncertainties cancel out Values close to 1 reflect the R AA flatness vs. centrality 22

23 normalized to 40-80% R CP Comparison with ATLAS result J/ψ R CP larger for ALICE than for ATLAS but different rapidity and p T coverage can play a role Pb-Pb s NN = 2.76 TeV ALICE, 2.5<y<4, p >0 (preliminary) T ALICE, ATLAS, y <0.8, y <2.5, pp>0 >6.5 (preliminary) T GeV/c (arxiv: ) T ATLAS, y <2.5, p >6.5 GeV/c (arxiv: ) T 40-80% 20-40% 10-20% 0-10% centrality ALICE: 2.5<y<4 p T > 0 ATLAS: y <2.5 80% of J/ψ with p T >6.5 GeV/c Inclusive J/ψ R CP can be also measured in ALICE at mid-rapidity in the dielectron channel Very challenging analysis error bars are still large. Wait for 2011 high luminosity run! 23

24 J/ψ in ultra-peripheral collisions Probe gluon distribution in the nuclei (down to x~10-4 ) Search for tracks in the central barrel (ITS+TOF) or muon spectrometer, with a veto on V0 detectors J/ψ e + e - J/ψ μ + μ - Visible J/ψ signals in ultra peripheral PbPb collisions 24

25 Prospects: J/ψ flow At LHC, J/ψ regeneration could play an important role and will dominate the J/ψ flow Several methods explored: here event plane method, using TPC tracks Y. Liu, N. Xu, P. Zhuang, Nucl.Phys.A834(2010) 317c Study is feasible, now waiting for larger data sample in

26 Summary and outlook The ALICE experiment has measured the inclusive J/ψ production in PbPb collisions at s NN = 2.76 TeV at both mid-rapidity and forward rapidity R AA normalized to J/ψ cross-section in pp at the same energy shows a clear suppression of the J/ψ yield with respect to Ncoll scaling forward values are larger than forward RHIC results R AA (R CP ) values are larger than those measured by CMS (ATLAS), but the kinematical coverage is different A deeper understanding requires a precise knowledge of cold nuclear matter effects: waiting for pa at LHC in 2012! Next 2011 PbPb run with >5 times L int (2010) should improve the quality of the measurements, allowing the study of J/ψ flow and production in ultra-peripheral collisions 26

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28 Comparison RHIC/SPS Comparison SPS and RHIC R AA comparison between SPS and RHIC CAVEAT: at SPS no pp data 158GeV need to build the reference extrapolating pa data to A=1 The initial estimate of the pp reference was obtained from pa data at higher energy, 450 GeV, (and rescaled to 158GeV) All R AA looked similar! but recently the pp reference was obtained directly from NA GeV the comparison looks different! pp reference is crucial to correctly interpret the results! picture not yet clear! 28

29 The muon spectrometer It is designed in order to have: large geometrical acceptance to increase dimuon statistics acceptance down to p T ~0 where direct J/ψ production dominates good mass resolution to separate the ϒ family tracking/trigger high granularity read-out to cope with the high multiplicity front absorber (10λ I ) tracking system (10 detection sub-planes, 70μm resolution in the bending plane) dipole magnet (3Tm) muon-filter wall (7λ I ) trigger chambers (4 planes, programmable p T cut, with p Tμ >0.5GeV/c) 29

30 Physics motivations Quarkonium suppression is considered since a long time as one of the most striking signatures for the QGP formation in AA collisions s GeV/c RHIC LHC 17 SPS ~ Year 30

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32 Quarkonium measurement in ALICE 3 sources of J/ψ Direct production Feed down from heavier charmonium states J/ψ from b-hadron decay ALICE results refer to inclusive J/ψ production Prompt J/ψ J/ψ from B feasible in the central barrel, thanks to the good impact parameter resolution (σ rφ < 75 μm for p T >1 GeV/c) forward detection more difficult 3-muon events B cross section from single muon measurement 32

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