Measurement of J/  production in Pb-Pb and pp collisions at the LHC with the ALICE experiment M. Gagliardi (Università degli Studi e Sezione INFN, Torino) for the ALICE Collaboration The 11 th International Conference on Nucleus-Nucleus collisions San Antonio, TX, USA – May 31 st,

Outline Motivation J/  detection in ALICE Results in pp collisions Results in Pb-Pb collisions Conclusions 2

- pp collisions Insight on quarkonium production at LHC energies: hadronisation of heavy quark pairs into a bound colourless state is highly non-perturbative -> challenge for models Reference for the study of nuclear modifications in heavy ion collisions - Pb-Pb collisions Resonance melting by colour screening in a Quark Gluon Plasma: one of the first proposed signatures of deconfinement ( T.Matsui, H. Satz, Phys. Lett. B 178 (1986) 416) Suppression beyond cold nuclear matter effects observed at SPS and RHIC (but similar magnitude in spite of different energy densities). J/  regeneration by statistical hadronisation of cc pairs might play a role and even become dominant at LHC energies (e.g., Andronic et al, Phys. Lett. B 652 (2007) 659) Detailed discussion by P. Zhuang and P. Braun-Munzinger in Plenary 2 and 3 Motivation Perturbative vacuum Colour screening 3

A Large Ion Collider Experiment 4 Muon spectrometer -4 <  < -2.5 Dipole magnet Front absorber 10 I 10 tracking planes (Cathode Pad Chambers) Trigger system (Resistive Plate Chambers) Muon filter in front of the trigger chambers (7 I ) Central Barrel |  | < 0.9 Solenoidal magnet Time Projection Chamber: -Tracking -PID via dE/dx Inner Tracking System (Silicon Pixel, Drift, Strip Detectors) - Vertexing - Tracking - Triggering (SPD ) Time of Flight MRPCs - PID VZERO scintillators - Triggering - Centrality in Pb-Pb - Luminosity Only detectors used in this analysis are discussed

5 J/  detection in ALICE Prompt : ~90 % From B-decay ~10% Directly produced ~50% Feed down from  ’,  c ~40% Inclusive Three sources of J/  (fractions refer to the p t -integrated yield) Central barrel: J/  -> e + e - |y| 0 Data setTriggerL int pp √s = 7 TeV (2010) Min bias (VZERO, SPD) 5.6 nb -1 pp √s = 2.76 TeV (2011) Min bias (VZERO, SPD) 1.1 nb -1 Pb-Pb √s NN = 2.76 TeV (2010) Min bias (VZERO, SPD) 1.7  b -1 Muon spectrometer: J/  ->  +  Data setTriggerL int pp √s = 7 TeV (2010) Min bias (VZERO, SPD) AND single  15.6 nb -1 pp √s = 2.76 TeV (2011) Min bias (VZERO, SPD) AND single  19.9 nb -1 Pb-Pb √s NN = 2.76 TeV (2011) Min bias (VZERO) AND  pair 70  b -1 Separation possibile in the electron channel in pp

pp collisions 6

7 J/  cross section measurement - Measurement down to zero transverse momentum in a broad rapidity range - p t -differential cross section at 2.76 and 7 TeV well reproduced by Non-Relativistic QCD (Colour Singlet +Colour Octet) TeV results used as reference in Pb-Pb analysis 7 TeV: Phys. Lett. B 704 (2011) TeV: arXiv: v1 [hep-ex]

8 J/  polarisation measurement - Polarisation is a crucial observable for the comparison between data and models - Measured via polar (  ) and azimuthal ( φ ) angle distributions of decay muons, analysed in two reference frames: Collins-Soper and Helicity 1 transverse polarisation 0 no polarisation -1 longitudinal polarisation   W (cos , φ )  1 +  cos 2  + φ sin 2  cos2 φ +  φ sin2  cos φ

9 J/  polarisation Data suggest weak or no polarisation Extended p t coverage will provide a more stringent test of the models Phys.Rev.Lett. 108 (2012) arXiv: v1 [hep-ex]  φ

10 Multiplicity dependence of J/  production - Highest multiplicity in this data-sample: dN ch /d  ~30 (i.e. 5 times the minimum bias multiplicity): comparable to semi-central Cu-Cu collisions at RHIC - Measurement of J/  production in high multiplicity collisions provides insights on the interplay between hard and soft regime in multi-partonic interactions - A linear increase of the relative J/  yield with the multiplicity is observed - Behaviour not reproduced by Pythia (v. 6.4) Phys. Lett. B 712 (2012) 165

11 J/  production from B-hadron decay TO BE UPDATED WITH ARXIV VERSION Good agreement among LHC (and Tevatron) experiments - Unique measurement at mid-rapidity and low p t - Good impact parameter resolution ( σ r φ 1 GeV/c) -> contribution from B estimated via the pseudo-proper decay length Fraction of J/  from B decay in p t > 1.3 GeV/c, |y|<0.9: f B = ±0.037(stat) (syst) (syst polar.) arXiv: v1 [hep-ex]

12 J/  production from B-hadron decay Extrapolation to p t = 0 to get prompt J/  cross section at mid-rapidity - Unique measurement at mid-rapidity and low p t - Good impact parameter resolution ( σ r φ 1 GeV/c) -> contribution from B estimated via the pseudo-proper decay length Fraction of J/  from B decay in p t > 1.3 GeV/c, |y|<0.9: f B = ±0.037(stat) (syst) (syst polar.) arXiv: v1 [hep-ex]

Pb-Pb collisions 13

J/  in Pb-Pb  trigger  centrality, track selection 14 Trigger Electrons (min bias) VZERO-A AND VZERO-C AND SPD Muons VZERO-A AND VZERO-C AND di-muon trigger (p t > 1 GeV/c) Centrality selection Glauber model fit of the VZERO amplitude Track selection Electrons: - identified via dE/dx in TPC: |n  e | pairs with|y ee | < 0.9 Muons - muon tracks are requested to have hits in the trigger chambers -> efficient hadron rejection due to the iron wall before the trigger system - pairs with 2.5<y  <4 PRL 106, (2011)

J/  in Pb-Pb  signal extraction Muons - Several shapes for background - Double Crystal Ball function for signal - Fit of signal + background 15 Electrons - Background from event-mixing - Scaling to same-event spectrum and subtraction - Signal from bin counting in 2.92 < M < 3.16 GeV/c 2 ~40000 J/  ~2000 J/ 

J/  in Pb-Pb  Ax  correction 16 Weak centrality dependence for both electrons (7.8% -8.9%) and muons (13.3%-14.5): Less than 10% loss of efficiency from peripheral to central events Computed from MC simulations with realistic detector configuration Electrons: HIJING events enriched with J/  -> ee Muons: J/  ->  embedded in real Pb-Pb events

17 J/  in Pb-Pb  nuclear modification factor R AA -Y J/  PbPb = N J/  PbPb / (A  BR N PbPb ) - R AA i = Y J/  PbPb,i / (T AA i  J/  pp ) (i th centrality bin)  J/  pp : pp data at √s = 2.76 TeV T AA i : Glauber MC Integrated R AA Forward rapidity: R AA 0-90% = ± (stat.) ± (syst.) (uncertainty is dominated by pp reference) Mid-rapidity: R AA 0-80% = 0.66 ± 0.10 (stat.) ± 0.24 (syst.) (uncertainty is dominated by signal extraction and pp reference) Clear J/  suppression at forward rapidity Data show weak centrality dependence for N part > 100 Similar pattern at mid-rapidity, but larger uncertainties Red: 2.5<y<4 Blue: |y|<0.9

J/  in Pb-Pb  nuclear modification factor R AA ALICE 2.5 < y < 4 Black: PHENIX - p t > 0, 1.2 < |y| <2.2 Blue: CMS - p t > 6.5 GeV/c, |y| < 2.4 PHENIX and CMS (at high p t ): R AA decreasing with centrality Transport models: 50% of regenerated J/  in the most central collisions Statistical hadronisation: all J/  produced at hadronisation 18 Red: ALICE - pt>0, 2.5<y<4

19 J/  R AA vs p t at forward rapidity R AA decreases with p t

20 J/  R AA vs p t at forward rapidity Red: ALICE 2.5 < y < 4 Blue: CMS |y| < 2.4 Black: PHENIX 1.2 < |y| < 2.2 New behaviour at low p t ?

21 J/  R AA vs p t at forward rapidity Reproduced by models with regenerated J/  component

22 J/  R AA vs rapidity R AA decreases with rapidity (by 40% from y = 2.5 to y =4)

23 J/  elliptic flow: v 2 Pressure gradients in a thermalised medium convert initial spatial anisotropy in momentum anisotropy dN/d  φ  1+v 2 cos (  φ )   φ  φ-  RP, RP = reaction plane The anisotropy is quantified by the v 2 coefficient J/  flow at LHC energies may be driven by regeneration or recombination of charm quarks; low and mid p t ranges are the most interesting J/  signal extracted in 6  φ  φ-  RP bins for 4 pt bins in 20%-60% centrality Event plane determined using three different subsets of detectors with large  gaps v 2 extracted from  φ distributions

24 J/  v 2 vs p t Hint for non-zero v 2 (2.2  significance) for 2 GeV/c < p t < 4 GeV/c

25 J/  v 2 vs p t Hint for non-zero v 2 (2.2  significance) for 2 GeV/c < p t < 4 GeV/c

26 J/  v 2 vs p t Hint for non-zero v 2 (2.2  significance) for 2 GeV/c < p t < 4 GeV/c Compatible with transport model predictions

27 Conclusions and outlook ALICE results on J/  production: in pp collisions - cross section down to p t =0 - beauty feed-down contribution - weak or null polarisation - linear increase of the yield with multiplicity Looking forward to p-Pb collisions (winter 2012), to constrain shadowing of nuclear structure functions at LHC energies in Pb-Pb collisions - weak or no centrality dependence of R AA at large N part - R AA is larger at low p t - significant decrease of R AA at large rapidities - hint for non-zero elliptic flow at low p t

Backup 28

29 Non-prompt J/  and bb cross section in pp collisions

30 J/  -> e + e - R AA : systematic uncertanties Uncorrelated in centrality: Correlated in centrality: - pp reference 26%

31 J/  ->  +  - R AA : systematic uncertanties Uncorrelated in centrality: Correlated in centrality: - Trigger efficiency 6.4% - Tracking efficiency 6% - MC J/  distribution 5% - Trigger matching efficiency and relative trigger normalisation: 2.8% - pp reference 8.2%

32 J/  R AA vs N part at high p t

33 J/  R AA : more model comparisons

34 J/  R AA : more model comparisons

35 J/  R AA : more model comparisons

36 Prompt J/  R AA

37 J/  v 2 vs centrality