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Going from NN to AA is indeed a major step

From Elementary to Nuclear Collisions: Evolution or Revolution? Helena Białkowska Institute for Nuclear Studies, Warsaw, Poland. Going from NN to AA is indeed a major step. It is usually instructive to go step-by-step Thus – look at NN, hA different centralities Will look at:

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Going from NN to AA is indeed a major step

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  1. From Elementary to Nuclear Collisions:Evolution or Revolution?Helena BiałkowskaInstitute for Nuclear Studies, Warsaw, Poland Wwa Oct 22, 2004

  2. Going from NN to AA is indeed a major step • It is usually instructive to go step-by-step • Thus – look at NN, hA different centralities • Will look at: total multiplicities baryon stopping transverse phenomena And this is NOT a comprehensive review, just some selective comments… Wwa Oct 22, 2004

  3. Multiplicitiesmidrapidity density vs predictions: AA central Pre-RHIC predictions Wwa Oct 22, 2004

  4. Total Multiplicity vs. Beam energy – compare to pp: Wwa Oct 22, 2004

  5. At midrapidity: Wwa Oct 22, 2004

  6. (dN/dyT ) e+e- scales likeAA near midrapidity Surprising comparison to e+e-: Wwa Oct 22, 2004

  7. Does it make sense to compare AA central to minbias pp? apples to oranges (or even worse: apples to appleseeds) Look at pp `central’ (high pt, old ISR data) AA central e+e- pp ‘normal’ Wwa Oct 22, 2004

  8. If not `centrality’ – perhaps `effective energy`? Old (Brenner et al., 1982, Basile 1980) observation for pp: ~half the energy goes into leading baryon pp  pX = pp  X if same effective energy `Effective energy’ ~ sqrt(s)/2 Wwa Oct 22, 2004

  9. Comparing pp at `effective energy’ to e+e-: (Caruthers et al.., on pp, e+e-, 1983 quoted by Gunther Roland) Wwa Oct 22, 2004

  10. Recall the steps: • Without any trick – AA central like e+e- • With an ‘effective energy’ trick: pp resembles e+e- • And henceforth – AA central! Wwa Oct 22, 2004

  11. So finally – ‘everything resembles everything’(although only for high energy) First shown By Peter Steinberg QM02 Wwa Oct 22, 2004

  12. Centrality dependence at fixed s: Wwa Oct 22, 2004

  13. sinel=42 mb (RHIC) sinel=33 mb (SPS) sinel=21 mb (low AGS) PHOBOS Glauber MC L~A1/3 Reminder: participants – collisions – impact patameter Ncoll Npart/2 ~ A Npart b Ncoll= # of NN collisions: ~A4/3 Wwa Oct 22, 2004

  14. More on centrality For different s For different reaction Scaling of multiplicities with number of participants Wwa Oct 22, 2004

  15. Another approach to pp vs AA:Marek Gazdzicki&Mark Gorenstein - presumed phase transition around sqrts ~ 5GeV Comparing AA central to pp (F ~ sqrt(sqrt(s))) Wwa Oct 22, 2004

  16. II. Evolution of baryon stopping/baryon number transfer • Usually ‘measured’ by p – pbar (not always justified at lower energies, because of asymmetric b bbar pair production) Wwa Oct 22, 2004

  17. How to include p-A: • Very unfriendly system – asymmetric! • Make good use of this asymmetry: separate target and projectile contributions • Caveat: this is already a model! • This model does have some support from elementary data: compare pp and p p Wwa Oct 22, 2004

  18. 200 GeV pA data from NA49(forward hemisphere) Wwa Oct 22, 2004

  19. Enter two-component model (following analysis – see Andrzej Rybicki @QM04) Wwa Oct 22, 2004

  20. How to separate projectile and targetcontributions to net baryons spectra Subtract <pA> Subtract <pp> Wwa Oct 22, 2004

  21. ‘target subtracted’ projectile component: Wwa Oct 22, 2004

  22. Forward hemisphere for centrality selected PbPb: Wwa Oct 22, 2004

  23. Can now compare: Wwa Oct 22, 2004

  24. Thus a smooth evolution, governed essentially by geometry (N of collisions) Wwa Oct 22, 2004

  25. III. Now for transverse characteristics: • This is a hot topic – because of ’jet quenching’ • Question: is the effect seen only at RHIC? • Is there a dramatic difference between hA and AA? Wwa Oct 22, 2004

  26. Nuclear modification factor: Wwa Oct 22, 2004

  27. SPS to RHIC: ’folklore’ knowledge: SPS: rise RHIC: quench Wwa Oct 22, 2004

  28. With a new analysis of pp data at SPS (D`Enterria@QM04): Onset of quench? Wwa Oct 22, 2004

  29. Jet quenching from azimuthal correlations: Central Au-Au Peripheral Au-Au Away side jet disappears Wwa Oct 22, 2004

  30. Yet from SPS CERES… Semi-central central Onset of disappearance for most central Pb-Au Wwa Oct 22, 2004

  31. What do we expect for p-A at high pT? Cronin effect a > 1 for pT > 1 Antreasyan 1979, sqrt(s) = 27.4, y ~0 Wwa Oct 22, 2004

  32. Midrapidity dAu data At RHIC: centrality More central – more enhanced Looks like Cronin Wwa Oct 22, 2004

  33. Nuclear modification factorfor p – Pb at SPS: NA49Bożena Boimska PhD thesisWarsaw Institute for Nuclear Studies, May04 Wwa Oct 22, 2004

  34. The evolution of R with x at SPS, intermediate pT (below 2 GeV/c) 200 GeV pPb (n = 5.8) Notice : at pT ~ 2 GeV/c R = 1 both at SPS and RHIC As we go forward – R decreases! Wwa Oct 22, 2004

  35. Particle species dependence at SPS pPb: Pions,pbar reach R=1 at pT ~2 GeV/c Protons already at ~1.2 Wwa Oct 22, 2004

  36. Going forward at RHIC: More forward – less enhanced, more suppressed! Remember, this is d – Au, all charged! Wwa Oct 22, 2004

  37. Evolution of R with h for dAu: Evolution of R with h for dAu: From Gabor Veres Buda `04 R up with pT down with h Wwa Oct 22, 2004

  38. Thus 2 effects observed at RHIC: suppression of high pT in central A – A (‘jet quenching’) and suppression of high pT at forward rapidities in p – A (‘gluon saturation’?, ‘color glass condensate’?) seem to appear already at SPS (interpretation pending...) Wwa Oct 22, 2004

  39. What is a Colored Glass Condensate, CGC? • ‘collective partonic state describing nuclei at small x’ • At small x for nuclear collisions – large number of gluons saturates • At forward rapidities – x very small • dense partonic state forms • Suppression ot yields for d-Au pre(post)dicted Wwa Oct 22, 2004

  40. To sum up: Multiplicities: An intriguing ‘scaling’ when compared at appropriate energy • Or a sudden jump? Wwa Oct 22, 2004

  41. Baryon stopping: • Smooth evolution , essentially governed by geometry (collisions, participants) • (more of this: see Wit Busza@PHOBOS) Wwa Oct 22, 2004

  42. Transverse spectra: • Intriguing onsets at SPS of phenomena dominant at RHIC Wwa Oct 22, 2004

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