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Charmonium production in heavy-ion collisions: status and prespectives

Charmonium production in heavy-ion collisions: status and prespectives. E. Scomparin INFN Torino (Italy). XLVIII International Winter meeting on Nuclear Physics, Bormio (Italy) 25-29 January 2010 in Memoriam of Ileana Iori. Outline.

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Charmonium production in heavy-ion collisions: status and prespectives

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  1. Charmonium production in heavy-ion collisions: status and prespectives E. Scomparin INFN Torino (Italy) XLVIII International Winter meeting on Nuclear Physics, Bormio (Italy) 25-29 January 2010 in Memoriam of Ileana Iori

  2. Outline Charmonia suppression in AA collisions: a 25 year-long story SPS RHIC LHC 17 GeV/c 200 GeV/c 5.5 TeV/c √s 1986 year ~1990 ~2000 ~2010 Last year, new high precision data (HERA-B, NA60, PHENIX/STAR) have become available significant improvements in the overall understanding of the charmonium behavior in the hot medium

  3. T/TC J/(1S) c(1P) ’(2S) Physics motivation: AA collisions Study of charmonium production/suppression in pp, pA and AA collisions AA collisions • Sequential suppression of the resonances is a thermometer of the temperature reached in the collisions • Charmonia suppression by color screening has been proposed, more than 20 years ago, as a signature of QGP formation

  4. Physics motivation: pp,pA collisions pp collisions (not covered by this talk) provide information on production models (CSM, NRQCD, CEM…) provide a reference for nuclear collisions results pA collisions understand the J/ behaviour in the cold nuclear medium (CNM)  complicate issue, because of many competing mechanisms: Final state: cc dissociation in the medium, final energy loss μ Initial state: shadowing, parton energy loss, intrinsic charm J/ μ p reference for the study of charmonia dissociation in a hot medium  approach followed at SPS and also at RHIC (with dAu data)

  5. AA Why CNM effects are so relevant ? • The cold nuclear matter effects present in pA collisions are • of course present also in AA and can mask genuine QGP effects • Most of them (in particular final state interaction) scale with L, • the mean thickness of nuclear matter crossed by the J/ pA J//Ncoll 1 J//Ncoll/nucl. Abs. Anomalous suppression! L L • It is very important to measure cold nuclear matter effects before • any claim of an “anomalous” suppression in AA collisions • Final state break-up is very important (expected to scale • with √sN )....

  6. But... .... there are many nuclear effect at play • Initial state • Shadowing • Various parameterizations • (EKS98, EPS08,EPS09, nDS, HKN,...) • with significant uncertainties • Enhancement at SPS energy • Depletion at LHC energy • Parton energy loss • Shifts back the x1 of the incoming parton c=0.5qL2 • Reduces the effective √s of the interaction producing the cc pair • Model-dependent • Parameters can be tuned e.g. on • Drell-Yan data  q ~ 0.1 GeV2/fm F. Arleo, JHEP 0211 (2002) 044

  7. Fixed target experiments

  8. Data sets from fixed target experiments (Relatively) large amount of fixed-target data (SPS, FNAL, HERA) AA collisions NA38S-U 200 GeV/nucleon, 0<y<1 (M.C. Abreu et al., PLB449(1999)128) NA50Pb-Pb 158 GeV/nucleon, 0<y<, pT<5 GeV (B. Alessandro et al., EPJC39 (2005)335) NA60In-In 158 GeV/nucleon, 0<y<1, pT<5 GeV (R. Arnaldi et al., PRL99(2007) 132302,Nucl. Phys. A 830 (2009) 345) pA collisions HERABp-Cu (Ti) 920 GeV,-0.34<xF<0.14,pT<5 GeV (I. Abt et al., arXiv:0812.0734) E866p-Be,Fe,W 800 GeV,-0.10<xF<0.93,pT<4 GeV (M. Leitch et al., PRL84(2000) 3256) NA50p-Be,Al,Cu,Ag,W,Pb,400/450 GeV,-0.1<xF<0.1,pT<5 GeV (B. Alessandro et al., EPJC48(2006) 329) NA3p-p p-Pt, 200 GeV, 0<xF<0.6, pT<5 GeV (J. Badier et al., ZPC20 (1983) 101) NA60p-Be,Al,Cu,In,W,Pb,U 158/400 GeV,-0.1<xF<0.35,pT<3 GeV (E. Scomparin et al., Nucl. Phys. A 830 (2009) 239)

  9. In-In Pb-Pb Fixed target results (before 2009) Anomalous J/ suppression in AA is evaluated wrt to a reference obtained extrapolating, from pA to AA, the CNM effects affecting the J/ pA collisions In the NA50 approach: all initial/final CNM effects are described through an effective abs. cross section absJ/ • obtained from pA at 400/450 GeV (NA50) absJ/ = 4.2±0.5mb, (J//DY)pp =57.5±0.8 (Glauber analysis) • extrapolated to AA assuming absJ/ (158 GeV) = absJ/ (400/450 GeV) (J//DY)pp rescaled from450/400 to 158 GeV ~e−ρLσabs AA collisions Observed suppression in AA exceeds nuclear absorption • Onset of the suppression at Npart 80 • Good overlap between Pb and In (R. Arnaldi et al., PRL99(2007) 132302)

  10. I. Abt et al., arXiv:0812.0734 pA collisions: new HERA-B data To understand the J/ dissociation in the hot matter created in AA collisions, cold nuclear matter effects have to be under control These effects are quantified, in pA collisions, in two ways: • E866 vs HERAB(similar √s)  agreement in the common xF range • E866/HERAB vs NA50   decreases when decreasing √s Strong xF dependence of  Satisfactory theoretical description still unavailable! (R. Vogt, Phys. Rev. C61(2000)035203, K.G.Boreskov A.B.Kaidalov JETP Lett. D77(2003)599) Because of the  dependence onxF and energy the reference for the AA suppression must be obtained under the same kinematic/energy domain as the AA data

  11. New pA data from NA60 NA60 has collected pA data (using 7 different targets): 158 GeV:no data available up to now.  First pA data at the same energy as AA collisions 400 GeV:already investigated by NA50 (cross check) A-dependence of the relative cross sections is fitted using the Glauber model and absis extracted shadowing neglected, as usual (but not correct!) at fixed target absJ/ (158 GeV) = 7.6 ± 0.7 ± 0.6 mb absJ/ (400 GeV) = 4.3 ± 0.8 ± 0.6 mb Very good agreement with the NA50 value Using • (158 GeV) = 0.882 ± 0.009 ± 0.008  (400 GeV) = 0.927 ± 0.013 ± 0.009 E. Scomparin et al., Nucl. Phys. A 830 (2009) 227

  12. Comparison between experiments:  vs xF NA60 pA results can be compared with  values from other experiments In the region close to xF=0, increase of  with √s • NA60 400 GeV • very good agreement with NA50 NA60 158 GeV: smaller , hints of a decrease towards high xF ? Systematic error on  for the new NA60 points ~0.01

  13. Comparison between experiments:  vs x1,2  pattern vs x1 at lower energies resembles HERA-B+E866 but systematically lower shadowing effects and nuclear absorption scale with x2 (V. Tram and F. Arleo, arXiv:0612043) clearly other effects are present

  14. 158 GeV free proton pdf EKS98 158 GeV free proton pdf Kinematic dependence of nuclear effects Interpretation of results not easy  many competing effects affect J/ production/propagation in nuclei • anti-shadowing (with large uncertainties on gluon densities!) • final state absorption…  need to disentangle the different contributions Size of shadowing-related effects may be large and should be taken into account when comparing results at different energies C. Lourenco et al., arXiv:09013054 without antishadowing: 7.6± 0.7± 0.6 mb absJ/ (158 GeV) with antishadowing (EKS) = 9.3± 0.7± 0.7 mb Significantly higher than the “effective” value

  15. Kinematic dependence of nuclear effects(2) Apart from shadowing, other effects not very well known, as parton energy loss, intrinsic charm may complicate the picture even more First attempts of a systematic study recently appeared (C. Lourenco, R. Vogt and H.Woehri, JHEP 0902:014,2009, INT Seattle workshop 2009, F. Arleo and Vi-Nham Tram Eur.Phys.J.C55:449-461,2008, arXiv:0907.0043 ) Clear tendency towards stronger absorption at low √s No coherent picture from the data  no obvious scaling of  or abs with any kinematical variable

  16. B. Alessandro et al., EPJC39 (2005) 335 R. Arnaldi et al., Nucl. Phys. A (2009) 345 What about anomalous suppression ? • Cold nuclear matter effects on J/ in AA collisions can be determined • by means of an extrapolation of pA results absshows an energy/kinematical dependence reference now obtained from 158 GeV pA data (same energy/kinematical range as the AA data, contrarily to what was done in the past) AA collisions shadowing affects not only the target, but also the projectile proj. and target antishadowing taken into account in the reference determination Using the new reference: In-In 158 GeV (NA60) Pb-Pb 158 GeV (NA50) • Central Pb-Pb: still anomalously suppressed • In-In: almost no anomalous suppression? R. Arnaldi, P. Cortese, E. Scomparin Phys. Rev. C 81 (2010), 014903

  17. Collider experiments: RHIC

  18. Data sets from RHIC Experiments PHENIXJ/e+e-|y|<0.35 & J/+- |y| [1.2,2.2] STARJ/e+e-|y|<1 AA collisions Au-Au 200 GeV/nucleonPHENIX, PRL 98 232301 (2007) Nucl.Phys.A 830 (2009) 331 Cu-Cu 200 GeV/nucleonPHENIX, PRL 101 122301 (2008) STAR, Phys. Rev. C 101 041902 (2009) pp, dA collisions pp 200 GeV/nucleonPHENIX, PRL 98, 232002 (2007) STAR, Phys. Rev. C 101 041902 (2009) dAu 200 GeV/nucleonPHENIX, Phys.Rev.C 77 024912 (2008) Nucl.Phys.A 830 (2009) 227 All data have been collected at the same collision energy (√s = 200 GeV) and (for each experiment) in the same kinematic domain

  19. pp results pp results essential to • understand the J/ production mechanism • provide a reference for AA collisions (RAA) arXiv:0904.0439 C.L. da Silva, Nucl. Phys. A 830 (2009) 227 RHIC J/ results are usually provided as in terms of nuclear modification factor The pp reference, used up to now, is based on Run 5  improvement expected from new Run 6 high statistics data

  20. AA results AuAu Phys. Rev. Lett 98, 232301 (2007) PRL 101, 122301 (2008) J/ suppression is stronger at forward rapidity wrt. to midrapidity Similar Npart dependence of RAA for CuCu and AuAu How can we intepret the RAA results ?

  21. Interpretation of the results Several theoretical models have been proposed in the past, starting from the following observations • RAA at forward y is smaller than at midrapidity • RAA at RHIC and SPS are similar, in spite of the very different √s Different approaches proposed: • Only J/ from ’ and c decays are • suppressed at SPS and RHIC • same suppression at SPS and RHIC • results do not show evidence for the sequential suppression • 2) Also direct J/ are suppressed at RHIC but cc multiplicity high  J/ regeneration ( Ncc2) contributes to the J/ yield The 2 effects may balance: suppression similar to SPS

  22. Recombination • Models including J/ regeneration • from heavy quark recombination • qualitatively describe the RAA data (and in particular the larger suppression observed at forward rapidity) X. Zhao, R. Rapp arXiv:0810.4566, Z.Qu et al. Nucl. Phys. A 830 (2009) 335 • A direct way for quantitative • estimate goes through cc cross section • No accurate measurement available • Indirect way • kinematic distributions and elliptic flow should be affected by regeneration In particular the J/ should inherit the positive heavy quark elliptic flow

  23. y Statistical hadronization J/ production by statistical hadronization of charm quarks (Andronic, BraunMunzinger, Redlich and Stachel, PLB 659 (2008) 149) • charm quarks produced in primary hard collisions • survive and thermalize in QGP • charmed hadrons formed at chemical freeze-out (statistical laws) • no J/ survival in QGP A. Andronic et al. arXiv:0805.4781 Agreement between data and model Recombination should be tested on LHC data!

  24. Phys. Rev. C 77, 024912 (2008) Backward Forward Mid y dAu, first estimates of CNM effects Similarly to SPS, CNM effects are obtained from dAu data RHIC data explore different x2 regions corresponding to  shadowing(forward and midrapidity)  anti-shadowing(backward rapidity) RdAu is fitted with a theoretical calculation assuming • nuclear modifications of the PDFs • breakup as a free parameter The result is then extrapolated to AA results from dAu Run 3 do not allow to draw conclusions on AA results, because of the large error on breakup

  25. EKS98: 0,1,…4,…mb The Run8 dAu data High statistics dAu data (Run8 ~ 30x Run3) are now available Peripheral ------------------------------------------------------------ Central a single value of break-up cannot reproduce the RCP ratios Fit RCP separately for each rapidity bin, look for the y-dependence of the break-up cross section (T. Frawley ECT*,INT quarkonium,Joint Cathie-TECHQM workshop)

  26. backward y forward y midrapidity RAA/RAA (CNM) Extrapolate to AA and compare with data breakup shows a strong rapidity dependence (T. Frawley Joint Cathie-TECHQM workshop) suppression beyond CNM effects is found to be similar at y=0 and at y=1.7 trend at high y is similar to the one observed by E866 Is the highest suppression at forward rapidity a CNM effect ?

  27. Comparison with SPS vs Npart SPS results on anomalous suppression can be compared with RHIC RAA results normalized to RAA(CNM) • For central collisions more important suppression in Au-Au (RHIC) with respect to Pb-Pb (SPS) Effect related to the higher energy density reached at RHIC ? still some model dependence also in this approach: Cu results are fitted using dAu, since dCu data do not exist

  28. Comparison with SPS Results can be shown as a function of the multiplicity of charged particles (~energy density, assuming SPS~RHIC) nice scaling btw SPS and RHIC! Comparison can also be done in terms of * Bjorken energy density energy density evaluation is based on several assumptions dET/d from WA98 data for SPS data  no dET/d for CuCu, so AuAu data at the same NPart are used • comparing results from different experiments is not easy, significant systematic errors

  29. Perspectives for the LHC

  30. Quarkonium physics at the LHC New scenarios will open up, thanks to the high beam energy Factor 10 (100) increase in charmonium (bottomonium) cross section with respect to RHIC  Bottomonium physics will be accessible High charm quark multiplicity (NCC~100)  J/ regeneration (not yet firmly established at RHIC) might become dominant Pb ion beams (√s=5.5 TeV) p-p collisions will be also studied (√s=7 – 14 TeV)

  31. ALICE ATLAS ALICE(+-) ALICE(e+e-) CMS(+-) ATLAS(+-) LHCb CMS 2.5<<4 -0.9<<0.9 -2.7<<2.7 -2.4<<2.4 Acc 70 MeV 30 MeV 70 MeV 35 MeV (M) 1.2 0.15 0.13 (7) 1.2 (5) S/B pT >2 GeV/c >0 GeV/c >0 GeV/c >2 GeV/c prompt/ displ. yes? yes? indirect id. yes Measurements at the LHC Charmonium measurements will be carried out by all the LHC experiments, in different kinematical regions Some features relative to J/ measurement in central PbPb collisions (LHCb plans still not finalized)

  32. ALICE ALICE is the LHC experiment dedicated to nucleus-nucleus collisions Central Barrel: -0.9<<0.9 e+e- decay channel Forward Muon Arm 2.5<<4 +- decay channel In proton-proton collisions: Measurement of differential distributions (y,pT) and polarization  to constrain production models  to provide a reference for AA Quarkonium production will be measured in both the central barrel and in the forward muon spectrometer in p-p and Pb-Pb collisions

  33. Quarkonium in ALICE (central PbPb) Quarkonium in central Pb-Pb collisions (106 s running time, L=51026cm-2 s-1) Central rapidity Forward rapidity • e- identification in TPC+TRD • integrated J/ acceptance ~29% •  identified in a Muon Spectrometer • integrated J/ acceptance ~35% (*) requires Level-1 trigger on e- Simulations with dNch/dy~3000 Simulations with dNch/dy~8000  significance still rather high smaller statistics compensated by background reduction Worst situation for the ’statistics , but much larger background

  34. Charmonium in Pb-Pb: physics studies With the expected 1–year statistics:  J/ suppression can be studied as a function of centrality and pT (up to ~10 GeV/c)  J/ polarization study will be performed as a function of pT • A fraction of the J/ produced at LHC comes from B-hadron decays •  useful to evaluate the beauty production cross section • need to be disentangled to study prompt J/ production At midrapidity prompt and secondary J/ can be discriminated thanks to the vertexing capabilities At forward y J/ from B can be determined only indirectly • Higher charmonia states (’, c) can be measured •  cleaner signal for theory • feasible in pp, more complicate in Pb-Pb (higher background, smaller significance)

  35. First dimuons in ALICE! First dimuons have been seen in ALICE in pp collisions at √s=900GeV, even if … not yet a J/!

  36. Conclusions • J/ suppression is a good observable for QGP studies but for a correct evaluation of anomalous effects, cold nuclear matter effects have to be under control J/ behaviour in cold nuclear matter is already a complicate issue: many competing initial/final state effects Many steps forward thanks to new high precision data • An anomalous J/ suppression has been observed at both SPS and RHIC Important to understand J/ behaviour from lower to higher energy in a coherent scenario • New data at LHC energy will soon be available! They will help to discriminate among the different processes (suppression, regeneration…) affecting the J/ • In the future, the “J/ picture” will be further sharpened by the • results from CBM, exploring high baryon-density matter, and • (hopefully) also from an NA60-like experiment filling the gap • between FAIR and top SPS energy

  37. Thanks !!!

  38. Extrinsic vs intrinsic production Furthermore CNM effects may depend on the assumed J/ production mechanisms (E. Ferreiro et al. arXiv:0809.4684) • intrinsic (gg  J/) • extrinsic (gg  J/ + g) (emission of a hard gluon) J/ produced through different partonic processes involve gluons in different x2 region different shadowing corrections

  39. High-pT J/ in Cu-Cu STAR (centrality 0-20% & 0-60%) PHENIX (minimum bias) RCuCu =1.4±0.4±0.2 (pT>5GeV/c)  RAA increases from low to high pT RCuCu up to pT = 9 GeV/c  suppression looks roughly constant up to high pT NA50: Pb-Pb Difference between high pT results, but strong conclusions limited by poor statistics Both results in contradiction with AdS/CFT+Hydro Increase at high pT already seen at SPS

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