Some results obtained at RHIC

1. Some results obtained at RHIC Anatoly Litvinenko litvin@moonhe.jinr.ru

2. Outline. • Introduction • RHIC. Short introdaction • Why we study nuclei-nuclei collisions? • A few definitions. • What can we expect from theory • Properties of produced hadronic matter (observables) • Energy density • equilibration time (elliptic flow) • jet qenching • Resonances melting (Debye scrinig) • Conclusions

3. Relativistic Heavy Ion Collider (RHIC)

4. 2 rings, 3.8 km circumference. Polarized p and Nucleus up to Au. Top energies (each beam): 100 GeV/nucleon Au-Au. 250 GeV polarized p-p. NIM, v.499, p. 235-880, (2003)

6. Why the collisons of heavy nuclei is interesting? Let us see on the space – time picture of collision pre-collision QGP (?) and parton production hadron reinteraction hadron production QCD phase diagram

7. The QGP in the early universe

8. The QGP in the early universe

9. What kind of transition is predicted by lattice QCD

10. Rough estimation – ideal mass less gas Bosons -- 1- degree of freedom: Fermions -- 1- degree of freedom: 2 quarks 3 quarks

11. Qualitative Lattice QCD F. Karsch, Lecture Notes in Physics 583 (2002) 209.

12. For

13. Questions to be answered (experiment) • What is the value of energy density? • If the statistical equilibration is achieved? • Observables and hadronic matter properties.

14. Rapidity Lorens boost Pseudorapidity Transverse mass

15. Stopping power Net baryons distribution

16. Stopping power 73 ± 6GeV / nucleon

17. b 2R ~ 15 fm Centrality determination Participant Region Spectators Spectators Peripheral collisoin, b  2R Central collision, b = 0

18. Centrality classification Geometrical cross section • Value of impact parameter • In percent from the geometrical cross section Centrality Corresponds to the region impact parameter

19. Spectator distribution for different centrality ZDC – Zero Degree Calorimeter

20. QUESTION I Can we achieved enough energy density in nuclei-nuclei collisions ? Can we make some conclusion about from experiment?

21. Energy density and Bjorken equation Historically energy density was estimated using final for

22. Energy density but crossing time For and Energy density is determined using final state

23. QUESTION I Can we achieved enough energy density in nuclei-nuclei collisions ? Can we make some conclusion about from experiment? Yes! Bjorken equation

24. QUESTION II Is equilibrium state of hot and dense hadronic matter achieved? What is conclusions about from experiment?

25. The answer is not evident. Asymptotic freedom Big equilibration time Small coupling constant High energy density

26. elliptic flow Elliptic flow Space eccentricity Coordinate space asymmetry  momentum space anisotropy

27. Elliptic flow • For big value of elliptic flow you need save space anisotropy for a long enough time • The value of elliptic flow is sensitive to the Equation of State (EoS) Importance of elliptic flow • Give information about equilibration time • Give information about EoS On the next slides shown how ensemble of free streaming particles lost space eccentricity

28. TIME = 0 fm/c,

29. TIME = 1 fm/c,

30. TIME = 2 fm/c,

31. TIME = 3 fm/c,

32. elliptic flow and space eccentricity

33. Sensitivity to nuclear EoS Science, Vol 298, Issue 5598, 1592-1596, 22 November 2002Determination of the Equation of State of Dense Matter Pawel Danielewicz, Roy Lacey, William G. Lynch Directed Flow: Elliptic flow:

34. QUESTION II Is equilibrium state of hot and dense hadronic matter achieved? What is conclusions about from experiment? The strong indication that YES.

35. Some designations It is not reasons to expect strong changes in observables because the transition is crossover Commonly accepted: sQGP for strongly-interacting Quark-Gluon Plasma QGP, pQGP,wQGP for weakly-interacting Quark-Gluon Plasma

36. Observables and space time structure of Heavy ion collisions

37. Observables and space time structure of Heavy ion collisions • Production of hard particles: • jets • heavy quarks • direct photons • Calculable with the tools of perturbative QCD

38. Observables and space time structure of Heavy ion collisions • Production of semi-hard particles: • gluons, light quarks • relatively small momentum: • make up for most of the multilplicity

39. Observables and space time structure of Heavy ion collisions • Thermalization • experiment suggest a fast thermalization (remember elliptic flow) • but this is still not undestood from QCD

40. Observables and space time structure of Heavy ion collisions • Quark gluon plasma

41. Observables and space time structure of Heavy ion collisions • Hot hadron gas

42. Particle ratio and statistical models • One assumes that particles are produced by a thermalizedsystem with temperature T and baryon chemical potential • The number of particles of mass mper unit volume is : These models reproduce the ratios of particle yields withonly two parameters

43. Particle ratios and statistical models

44. One more observable. Particle ratios N/p ratio shows baryons enhanced for pT < 5 GeV/c

45. JET Quenching Jet: A localized collection of hadrons which come from a fragmenting parton Modification of Jet property in AA collisions because partons propagating in colored matter lose energy. One of the possible observable The suppression of the high- hadrons In AA collisions Was predicted in a lot of works. Some of them (not all) are: • J.D.Bjorken (1982), Fermilab – PUB – 82 – 059 - THY. • M.Gyulassy and M.Palmer, Phys.Lett.,B243,432,1990. • X.-N.Wang, M.Gyulassy and M.Palmer, Phys.Rev.,D51,3436,1995. • R.Baier et al., Phys.Lett.,B243,432,1997. • R.Baier et al., Nucl.Phys.,A661,205,1999

46. High pT (> ~2.0 GeV/c) hadrons in NN h d A Parton distribution functions a b c Hard-scattering cross-section B h Fragmentation Function

47. High pT (> ~2.0 GeV/c) hadrons in NN h d A Parton distribution functions a b c Hard-scattering cross-section B h Fragmentation Function

48. Suppression of high-pt hadrons. Qualitatively. Nuclear modification factor From naive picture is what we get divided by what we expect.

49. First data in first RHIC RUN Jet Quenching ! Great! But (see the next slide)

50. Nuclear modifications to hard scattering Large Cronin effect at SPS and ISR Suppression at RHIC Is the suppression due to the medium? (initial or final state effect?)