Measurement of J/ production in Pb-Pb and pp collisions at the LHC with the ALICE experiment M. Gagliardi (Universit 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 ( ) 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 , ) 1 + cos 2 + sin 2 cos2 + sin2 cos 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] 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 ( r 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| contribution from B estimated via the pseudo-proper decay length Fraction of J/ from B decay in p t > 1.3 GeV/c, |y| 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 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