Charmonia in Heavy Ion Collisions

1. Charmonia in Heavy Ion Collisions Roberta Arnaldi INFN Torino (Italy) Strongly Interacting Matter Under Extreme Conditions Hirschegg, 17-23 January 2010

2. Outline Charmonia suppression in AA collisions is already a 25 years long story SPS RHIC LHC 17 GeV/c 200 GeV/c 5.5 TeV/c √s 1986 years 1990 ~2000 2010 Last year, new high precision data (HERA-B, NA60, PHENIX/STAR) have been presented improvements in the understanding of the charmonium behavior, taking advantage of the different energy and kinematics exploited domains

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 has been proposed, more than 20 years ago, as a signature for QGP formation

4. μ J/ μ p 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 allow the understanding the J/ behaviour in the cold nuclear medium  complicate issue, because of many competing mechanisms: Final state: cc dissociation in the medium, final energy loss Initial state: shadowing, parton energy loss, intrinsic charm provide a reference for the study of charmonia dissociation in a hot medium  approach followed at SPS and similarly at RHIC (with dAu data)

5. Fixed target experiments

6. Fixed target experimental landscape (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 HERAB p-Cu (Ti) 920 GeV,-0.34<xF<0.14,pT<5 GeV (I. Abt et al., arXiv:0812.0734) E866 p-Be,Fe,W 800 GeV,-0.10<xF<0.93,pT<4 GeV (M. Leitch et al., PRL84(2000) 3256) NA50 p-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) NA60 p-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)

7. In-In Pb-Pb Fixed target experimental results 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 at 158 GeV 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)

8. I. Abt et al., arXiv:0812.0734 Cold nuclear matter effects To understand the J/ dissociation in the hot matter created in AA collisions, cold nuclear matter effects have to be under control These effects can be 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

9. New NA60 pA data 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

10. 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

11. 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

12. 158 GeV free proton pdf EKS98 158 GeV free proton pdf Kinematical 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

13. 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

14. B. Alessandro et al., EPJC39 (2005) 335 R. Arnaldi et al., Nucl. Phys. A (2009) 345 Reference for AA data a precise reference for the J/ behavior in AA collisions can be determined 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 In-In 158 GeV (NA60) Pb-Pb 158 GeV (NA50) Using the new reference: • Central Pb-Pb: still anomalously suppressed • In-In: almost no anomalous suppression? In-In analysis based on another centrality estimator (number of tracks) ongoing, to check the observed pattern R.A., P. Cortese, E. Scomparin Phys. Rev. C 81, 014903

15. Collider experiments

16. Collider experimental landscape Data from RHIC, waiting for high energy LHC collisions… Experiments PHENIXJ/e+e-|y|<0.35 & J/+- |y| [1.2,2.2] STAR J/e+e-|y|<1 AA collisions Au-Au 200 GeV/nucleon PHENIX, PRL 98 232301 (2007) Nucl.Phys.A 830 (2009) 331 Cu-Cu 200 GeV/nucleon PHENIX, PRL 101 122301 (2008) STAR, Phys. Rev. C 101 041902 (2009) pp, dA collisions pp 200 GeV/nucleon PHENIX, PRL 98, 232002 (2007) STAR, Phys. Rev. C 101 041902 (2009) dAu 200 GeV/nucleon PHENIX, Phys.Rev.C 77 024912 (2008) Nucl.Phys.A 830 (2009) 227 All data have been collected with the same collision energy (√s = 200 GeV) and kinematics

17. pp experimental results pp results should help 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

18. AA experimental results AuAu Phys. Rev. Lett 98, 232301 (2007) PRL 101, 122301 (2008) J/ suppression is stronger at forward rapidity wrt. to midrapidity The Npart dependence of RAA for CuCu and AuAu is consistent

19. Phys. Rev. C 77, 024912 (2008) Backward Forward Mid y CNM effects from dAu In a similar way as at SPS, CNM effects are obtained from dAu data RHIC data exploit different x2 regions corresponding to  shadowing (forward and midrapidity)  anti-shadowing (backward rapidity) RdAu is fitted with a theoretical calculation assuming • nuclear modified PDF distibutions • breakup The result is the extrapolated to AA results from dAu Run 3 do not allow to draw conclusions on AA results, because of the large breakup error

20. CNM effects from dAu (2) Furthermore CNM effects may depend on the assumed J/ production mechanisms (E. Ferreiro et al. arXiv:0809.4684) • intrinisic (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

21. EKS98: 0,1,…4,…mb The Run8 dAu data Now high statistics dAu data (Run8 ~ 30x Run3) are available • a single value of break-up cannot reproduce the RCP ratios RCP flat vs centrality at backward rapidity, but falls at forward y A new approach has been proposed, to evaluate CNM effects (T. Frawley ECT*,INT quarkonium,Joint Cathie-TECHQM workshop) a breakup for each y range • a shadowing parameterization RCP vs. centrality is fitted for each y bin with

22. backward y forward y midrapidity RAA/RAA (CNM) Result is then extrapolated to AA breakup shows a strong rapidity dependence the trend at high y is similar to the one observed by E866 the suppression beyond CNM effects is found to be similar at y=0 and at y=1.7 There is essentially no dependence of these results on the shadowing model used to parameterize the dAu RCP (T. Frawley Joint Cathie-TECHQM workshop)

23. Comparison with SPS results vs NPart Measured/Expected SPS results are compared with RHIC RAA results normalized to RAA(CNM) • Both Pb-Pb and Au-Au seem to depart from the reference curve at NPart~200 • For central collisions more important suppression in Au-Au with respect to Pb-Pb Systematic errors on the CNM reference are shown for all points still some model dependence also in this approach: Cu results are fitted using breakup from dAu, since dCu data do not exist

24. Comparison with SPS results Results are shown as a function of the multiplicity of charged particles (~energy density, assuming SPS~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 complicate issue, in particular when comparing results from different experiments

25. 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: 1) Only J/ from ’ and c decays are suppressed at SPS and RHIC same suppression is expected at SPS and RHIC  results do not seem to reflect 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

26. Recombination Models including J/ regeneration qualitatively describe the RAA data (X. Zhao, R. Rapp arXiv:0810.4566, Z.Qu et al. Nucl. Phys. A 830 (2009) 335) Direct way for quantitative estimate  accurate measurement of charm  Indirect way some distributions should be affected by regeneration J/ elliptic flow  J/ should inherit the positive heavy quark flow J/ y distribution  should be narrower wrt pp J/ pT distribution  should be softer (<pT2>) wrt pp Results are not precise enough to assess the amount of regeneration

27. 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

28. 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 Good agreement between data and model Recombination should be tested on LHC data!

29. LHC perspectives

30. Quarkonium physics at LHC New scenarios will be accessible, thanks to the high beam energy Factor 10 (100) increase in charmonia (bottomonia)  with respect to RHIC  Bottomonium physics will be accessible High charm quark multiplicity (NCC~100) J/ regeneration (not yet well defined at RHIC) might become dominant Pb ions will be accelerated (√s=5.5 TeV) 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 Charmonium performances @ LHC Charmonia measurements will be carried out by all the LHC experiments under different kinematical conditions Comparison of J/ measurement in central PbPb collisions Simulations with dNch/d~2500-5000

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 Quarkonium physics that will be addressed: • Suppression of in AA collisions • to study the created medium • Differential distributions • (y,pT,polarization) •  to constrain production models •  to provide a reference for AA Quarkonium production will be measured in the central barrel and in the forward muon spectrometer in p-p and Pb-Pb collisions

33. Quarkonium in central Pb-Pb 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 ~4.6% Simulations with dNch/dy~3000 Simulations with dNch/dy~8000 J/ and  significances not so differentsmaller statistics compensated by background reduction Worst situation for the ’ statistics , but much larger background

34. Quarkonium in Pb-Pb With the expected statistics (~7 105 J/ in 1 month of data taking): J/ suppression can be studied as a function of centrality and pT (up to ~10GeV/c), allowing the discrimination between the different theoretical scenarios J/ polarization study will be performed as a function of pT • A fraction of the J/ produced at LHC comes from the B hadron decay •  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, much more complicate in Pb-Pb because of the lower significance

35. First ALICE dimuons! First dimuons seen in ALICE in pp at √s=900GeV, even if out of the ~20 observed dimuons… not yet a J/!

36. Conclusions J/ suppression is a good signature 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 Signal of anomalous suppression has been observed at SPS and RHIC Important to understand J/ behaviour from lower to higher energy in a coherent scenario New LHC data 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 enriched by the results from CBM, exploring a baryon rich matter, and maybe from a NA60-like experiment filling the gap between FAIR and top SPS energy

37. Backup

38. NA60 pA data NA60 has collected pA data: 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)  3-day long data taking, largely motivated by the need of a reference sample taken in the same conditions of In-In (NA60) and Pb-Pb (NA50) data  useful to enlarge the  vs xF systematics 158 GeV •  bulk of the NA60 p-A data taking •  results released up to now • sub-sample with same exp. set-up used at 158 GeV • useful as a cross-check (same energy/kinematic domain • of the large statistics data sample collected by NA50) 400 GeV 0.28 < ycm < 0.78 (158 GeV) Kinematical window where acceptance is >0 for all targets • 3.2 < ylab < 3.7 -0.17 < ycm < 0.33 (400 GeV) • | cos CS | <0.5

39. NJ/  2  103 DY J/, ’ DD Comb.bck. p-Pb New NA60 pA results Not enough DY statistics to extract (as in NA50) B J//DY target by target Estimate of nuclear effects through relative cross sections: • all targets simultaneously on the beam • beam luminosity factors Niinc cancel out (apart from a small beam attenuation factor)  no systematic errors • each target sees the vertex spectrometer under a (slightly) different angle • acceptance and reconstruction efficiencies do not completely cancel out Efficiency map (4th plane, sensor 0) These quantities, and their time evolution, are computed for each target separately

40. Comparison between experiments: abs vs xF absJ/ calculated from cross section ratios for HERA-B, E866,NA3 As already observed for , there is: • a strong xF dependence • a √s dependence…butNA3 shows values closer to the high energy experiments (E866/HERA-B)

41. B. Alessandro et al., EPJC39 (2005) 335 R. Arnaldi et al., PRL99 (2007) 132302 new reference Results with old and new reference absJ/ (158 GeV) > absJ/ (400 GeV) smaller anomalous suppression expected with respect to previous results In-In 158 GeV (NA60) Pb-Pb 158 GeV (NA50) published results Anomalous suppression in In-In is quite small ( 10%) Anomalous suppression in Pb-Pb up to 30% In-In analysis based on another centrality estimator (number of tracks) ongoing, to check the observed pattern

42. Antishadowing contribution In AA collisions the initial state effects (shadowing) affect not only the target, but also the projectile proj. and target antishadowing taken into account in the reference determination Even in absence of anomalous suppression, the use of the standard reference (no shadowing) induces a 5-10% suppression signal  sizeable effect Using the new reference (shadowing in the projectile and target) • Central Pb-Pb: still anomalously suppressed • In-In: almost no anomalous suppression? R.A., P. Cortese, E. Scomparin Phys. Rev. C 81, 014903

43. Phys. Rev. C 77, 024912 (2008) y CNM effects from dAu As discussed for SPS data, a good knowledge of the initial/final state effects in nuclear matter helps to understand the J/ behaviour in AA CNM effects at RHIC energies can be inferred from dAu data, using different approaches 1st method • RdAu is fitted with a theoretical calculation assuming a shadowing parameterization and a breakup common to the whole y range. • The result is the extrapolated to AA • Since breakup iscommon, results in the two y ranges strongly depend on nPDF

44. PRL 101, 122301 (2008) Npart CNM effects from dAu 2nd method • RdAu data are fitted with a theoretical model including a breakup for each y range and shadowing parameterization • Results are limited by the low Run 3 statistics 3rd method • The approach is based on a combination of RdAu data at different y, to predict CNM RAA for AuAu J. Phys. G34, S955 (2007) • The method works only for AuAu, since RdAu is used directly • Results at different y are independent, but they again suffer the Run 3 low statistics

45. abs vs. y

46. 0-1.5% RCP pT (GeV/c) 33-47% RCP pT (GeV/c) High pT J/ @ SPS NA60: In-In @ 158 GeV pT dependence of the J/ suppression already investigated at SPS energies:  strong pT dependence of RCP only the low pT J/ψ are suppressed ! NA50: Pb-Pb @ 158 GeV

47. PHENIX First Upsilon results @ RHIC STAR dAu @√s=200GeV PHENIX, STAR pp @ √s=200GeV Cross section follows CEM expectations RdAu = 0.98 ± 0.32 ± 0.28 PHENIX Au-Au @ √s=200GeV consistent with Nbin scaling • Upsilons suppressed: very low statistics RAuAu [8.5,11.5] < 0.64 at 90% C.L. in the future: • as expected from CNM + sequential melting • Upcoming 50 pb-1 200 GeV p+p run (5.6 pb-1 in run6 p+p) • RHIC II: high luminosity → separation of 1S, 2S, 3S states

48. …and more results on… STAR pp @ √s=200GeV Small bck contribution allows the study of high pT J/ - hadron azimuthal correlations • from the comparison with model calculations BJ/ fraction = 13% ±5% STAR: arXiv:0904.0439 PHENIX pp @ √s=200GeV J/ azimuthal flow measurement limited by statistics • v2 = –10 ± 10 %@ |y|<0.35 & –9.3 ± 9.2 %@1.2<|y|<2.2 • does not allow to differentiate between different models in the measure pT range PHENIX AuAu@√s=200GeV First measurement of J/ψ photoproduction in ultraperipheral collisions  cross section (7633(stat)11(syst) b) consistent with theoretical predictions N(J/) = 9.9  4.1  1.0

49. Sequential melting In a color screening suppression scenario, a sequential melting, starting from the most loosely bound charmonia state, is expected are the SPS and RHIC J/ suppression in the hot medium similar enough to justify this assumption? can the c and ’ feed down account for the observed J/ suppression? are other mechanisms (e.g. color glass condensate) needed to explain the different suppression at midrapidity vs forward rapidity?

50. Thews Eur.Phys.J C43, 97 (2005) Grandchamp, Rapp, Brown PRL 92, 212301 (2004) Recombination In a dense medium, J/ may be formed by a c and a c belonging to a different initial cc pair regeneration is expected to be more important at midrapidity A good accuracy in the open charm cross section measurement should help to quantify the importance of this process RHIC patterns are qualitatively reproduced