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Quark Matter 2012, Washington, August 13 th -18 th 2012

J/  and (2S) production in Pb-Pb collisions with the ALICE Muon spectrometer at the LHC. Roberta Arnaldi INFN Torino (Italy) for the ALICE Collaboration. Quark Matter 2012, Washington, August 13 th -18 th 2012.

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Quark Matter 2012, Washington, August 13 th -18 th 2012

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  1. J/ and (2S) production in Pb-Pb collisions with the ALICE Muon spectrometer at the LHC Roberta Arnaldi INFN Torino (Italy) for the ALICE Collaboration Quark Matter 2012, Washington, August 13th-18th2012

  2. J/ and (2S) production in Pb-Pb collisions with the ALICE Muon spectrometer at the LHC Results from the 2011 Pb-Pb run on: centrality of the collisions transverse momentum (rapidity*) J/ differential RAA versus Comparison with theoretical models J/ <pT> and <pT2> (2S) production in Pb-Pb collisions * See I. Arsene, parallel 2D

  3. Quarkonia suppression Quarkonia suppression is considered, since a long time, as one of the most striking signatures for QGP formation in AA collisions Sequential quarkonia suppression: Information on the initial temperature of QGP …but many effects to be taken into account: cold nuclear matter, cc (re)combination Puzzles from SPS and RHIC • RHIC: stronger suppression at forwardrapidities • SPS vs. RHIC: similar RAA pattern versus s LHC results can give decisive inputs, investigating at higher QGP temperature, the role of • the large charm quark multiplicity • (( • other quarkonia states (bottomonium)

  4. Quarkonia measurement in ALICE Quarkonium in ALICE can be measured in two ways: Central Barrel J/e+e- (|y|<0.9) Electrons tracked using ITS and TPC Particle identification: TPC (+TOF) Forward muon arm J/+- (2.5<y<4) Muons identified and tracked in the muon spectrometer I. Arsene, parallel 2D Acceptance coverage in both y regions down to zero pT µ+ e- e+ ALICE results refer to inclusive J/ production µ-

  5. Pb-Pb collisions at sNN=2.76 TeV Results from 2011 data set, based on dimuon triggered events Integrated luminosity ~ 70 b-1 Event selection: Rejection of beam gas and electromagnetic interactions (VZER0 and ZDC) SPD used for vertex determination VZERO Centrality selection: Estimate based on a Glauber model fit of the VZERO amplitude • Muon track selection: • Muon triggermatching • -4<ημ<‐2.5 • 17.6<Rabs<89cm • (Rabs= track radial position at the absorberend) • 2.5<yμμ<4

  6. J/ +- signal • J/ yield extracted fitting the opposite sign dimuon invariant mass spectrum 0-90% centrality, pT>0 GeV/c Signal: shape described by an extended Crystal Ball function Background: several methods used (different fitting functions, event mixing) Results obtained with the different techniques are combined to extract <NJ/ψ> and to evaluate systematic uncertainties

  7. J/ +- signal • J/ yield extracted fitting the opposite sign dimuon invariant mass spectrum 0-90% centrality, pTbins Signal: shape described by an extended Crystal Ball function Background: several methods used (different fitting functions, event mixing) Results obtained with the different techniques are combined to extract <NJ/ψ> and to evaluate systematic uncertainties Thanks to the high statistics 2011 sample, J/ yields can be extracted also in narrow kinematic bins (y, pT and/or centrality)

  8. J/acceptance x efficiency Acceptance x efficiency computed embedding MC J/’s into real events Weak centrality dependence of the J/ efficiency (decreasing from 14.5% to 13.3% from peripheral to central collisions)

  9. J/RAA vs. centrality Clear J/ suppression with almost no centrality dependence above Npart~100 RAA0-90% (inclusive J/) = 0.497  0.006(stat) 0.078 (sys) J/measured inpp @s=2.76 TeV used as reference (arXiv:1203.3641) Negligible effect on RAA from non-prompt J/

  10. J/RAA vs. centrality Clear J/ suppression with almost no centrality dependence above Npart~100 RAA0-90% (inclusive J/) = 0.497  0.006(stat) 0.078 (sys) J/measured inpp @s=2.76 TeV used as reference (arXiv:1203.3641) Negligible effect on RAA from non-prompt J/ Comparison with PHENIX: weaker centrality dependence and smaller suppression for central events

  11. J/RAA vs. centrality Clear J/ suppression with almost no centrality dependence above Npart~100 RAA0-90% (inclusive J/) = 0.497  0.006(stat) 0.078 (sys) J/measured inpp @s=2.76 TeV used as reference (arXiv:1203.3641) Negligible effect on RAA from non-prompt J/ Comparison with PHENIX: weaker centrality dependence and smaller suppression for central events Comparison with models: Models including a large fraction (> 50% in central collisions) of J/ produced from (re)combination or models with all J/ produced at hadronization can describe ALICE results in central collisions. Interesting, in this context, to look also at J/ v2 H. Yang, parallel 7A

  12. J/RAA vs. centrality in pT bins J/ production via (re)combination should be important at low pT Comparison of the RAAcentrality dependence of low (0<pT<2 GeV/c) and high (5<pT<8 GeV/c) pT J/ 0<pT<2 GeV/c 5<pT<8 GeV/c Different suppression for low and high pT J/ Smaller RAA for high pT J/ • Errors: • uncorrelated (box around points) • partially correlated within and between sets ([]) • 100% correlated within a set and between sets (text)

  13. J/RAA vs. centrality in pT bins J/ production via (re)combination should be important at low pT Comparison of the RAAcentrality dependence of low (0<pT<2 GeV/c) and high (5<pT<8 GeV/c) pT J/ 0<pT<2 GeV/c primordial Different suppression for low and high pT J/ Smaller RAA for high pT J/ recombination In central collisions, these models (X. Zhao et al, Y.P. Liu et al, E. Ferreiro) predict ~50% of low pT J/ to be produced via (re)combination, while at high pT the contribution is negligible 5<pT<8 GeV/c primordial recombination

  14. J/RAA vs. pT As an alternative view, RAA is shown as a function of the J/pT for various centrality bins 0-20% vs40-90% 0-90% Splitting in centrality bins we observe that the difference low vs high pTsuppression is more important for central collisions Suppression is stronger for high pT J/ (RAA~0.6 at low pT and ~0.35 at high pT)

  15. J/RAA vs. pT As an alternative view, RAA is shown as a function of the J/pT for various centrality bins 0-20% vs40-90% 0-90% total recombination Splitting in centrality bins we observe that the difference low vs high pTsuppression is more important for central collisions Suppression is stronger for high pT J/ (RAA~0.6 at low pT and ~0.35 at high pT) Fair agreement between data and models including a large contribution from (re)combination (~50% in central and ~30% in peripheral collisions)

  16. J/pT spectra Comparison with lower energy results can be carried out by comparing <pT> and <pT2> vs centrality J/ <pT> and <pT2> values are extracted from fits to d2N/dydpT

  17. J/<pT> and <pT2> The J/ <pT> and <pT2> show a decreasing trend as a function of centrality, confirming the observation that low pT J/ are less suppressed in central collisions The trend is different wrt the one measured at lower energies, where an increase of the <pT> and <pT2> with centrality was observed

  18. (2S) in pp and Pb-Pb collisions The (2S) yield is compared to the J/ one in Pb-Pb and in pp Charmonia yields are extracted fitting the invariant mass spectrum in two pT bins: 0<pT<3 and 3<pT<8 GeV/c and, for Pb-Pb, also as a function of centrality pp@s=7TeV Pb-Pb@sNN=2.76TeV Pb-Pb: S/B (at 3  around the (2S)) varies between 0.01 and 0.3 from central to peripheral collisions

  19. (2S)/J/double ratio Reference: pp data @s=7TeV (small s- and y-dependence from [(2S)/J/]ppresults by CDF, LHCb and CMS taken into account in the syst. uncertainty). (Error on the reference is shown as dashed line) Main systematic uncertainties (some sources cancel out in the double ratio) are the signal extraction and the choice of the MC inputs for acc. calculation Large statistics and systematic errors prevent a firm conclusion on the (2S) enhancement or suppression versus centrality ALICE result, in central collisions, does not show a large (2S) enhancement

  20. Conclusions The J/ nuclear modification factor has been measured in Pb-Pb collisions at forward rapidity, down to pT=0 • RAA centrality and pT dependence have been presented • RAAvs centrality saturates (RAA~0.4) beyond Npart =100 • Less suppression at low with respect to high pT, with • stronger pT dependence for central events • Lower energy experiments show an opposite behaviour • (see pT  vs Npart) Models including J/ production via (re)combination succeed in describing ALICE results in central collisions A still deeper understanding requires a precise knowledge of cold nuclear matter effects: waiting for pA at LHC in 2013! First ALICE results on (2S) : no firm conclusions on enhancement or suppression with respect to J/, but strong enhancement for central Pb-Pb collisions is unlikely

  21. Backup

  22. Systematic uncertainties on differential RAA • Type A: • uncorrelated • (shown as filled box around points) • Type B: • partially correlated within and between sets(shown as [] around points) • Type C: • 100% correlated within a set and between sets (global quantity for all sets) For the RAA versus centrality: • Type A: • signal extraction • Type B: • uncorr. syst on pp, MC inputs, trigger, tracking, matching, TAA • Type C: • normalization, corr. syst on pp

  23. Signal extraction Signal extraction: evaluated separately for each centrality/y/ptbin J/ and (2S) yields obtained as weighted average of results from several approaches based on 1) Fit to the invariant mass spectrum 2) Fit to the signal after event mixing background subtraction Systematic uncertainties on the signal extraction are given by the RMS of the distributions Fitting procedure: • Fit with a Double CB + variable width Gaussian (case 1) • Fit with a Double CB + pol0 (case 2) • (other background functions, different CB2 tails values, different assumptions for J/ width tested and included in the systematic uncertainty extraction)

  24. J/RAA vs. centrality in pT bins

  25. J/RAA vs. pT in centrality bins

  26. J/RAA vs. centrality in y bins

  27. J/RAA vs. rapidity 2.5<y<3 3.5<y<4 Suppression increases with centrality and it is stronger in the more forward region Inclusive J/ measured also as a function of rapidity:RAA decreases by 40% from y=2.5 to y=4

  28. J/RAA vs. rapidity Suppression increases with centrality and it is stronger in the more forward region Inclusive J/ measured also as a function of rapidity:RAA decreases by 40% from y=2.5 to y=4 Suppression beyond the current shadowing estimates. Important to measure cold nuclear matter effects (incoming pA data taking) Comover+regeneration model seems to predict a weaker rapidity dependence

  29. RAA versus centrality

  30. Influence on RAA of J/ from B decay Inclusive J/ measured in ALICE Estimate of prompt J/ RAA using: • b-fraction measured by CDF, CMS and LHCb • Interpolation at s= 2.76 TeV • Different b-quenching hypothesis from RAA(B)=0.2 to RAA(B)=1 J/ from b-hadrons decays have a negligible influence on our measurements

  31. Comparison ALICE vs CMS and PHENIX

  32. Theoretical model: contributions

  33. J/<pT2> vs centrality

  34. (2S)/ J/in pp collisions

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