Structure and Fine Structure seen in e + e - , pp, pA and AA Multiparticle Production

1. BNL workshop, May 2004 Structure and Fine Structure seen in e+e-, pp, pA and AA Multiparticle Production Wit Busza MIT

2. In high energy heavy ion collisions a fascinating highly interacting medium is produced Aim of talk: Look at the main longitudinal features in pp, pA, dA and AA multiparticle production to see if we can get some insight into what is happening during the collision process By-product: reminder of some relevant facts seen in pA collisions

3. Bottom line, for center of mass energies >10GeV: Structure (<20% accuracy): Multiplicities and rapidity distributions in e+e-, pp, pA and AA are the same provided one takes the appropriate normalization and the appropriate energy. - the approriate normalization for symmetric collisions is Npart/2 and for asymmetric ones it is a linear function of rapidity, at each end proportional to the number of incident participants. - the appropriate energy is the same for ee and AA (√SNN ), and for pp, pA and dA it is approximately 2 √SNN . 2. The basic structure of dn/dy is approximately a gaussian, whose growth with energy is primarily determined by an ever increasing “limiting fragmentation region” (related to the increase of the rapidity of the incident particles) -

4. Fine Structure (<10% accuracy): 1. Independent of energy, increasing Npart redistributes the particles in rapidity, keeping the total per participant constant, in such a way that a). The increase in mid-rapidity dn/dy is proportional to Npart b). The number of particles at the larger values of y decrease correspondingly (note: energy conservation is presumably satisfied by changes in the transverse momentum of particles) Nuclear fragments or cascading of particles slightly increases the density of particles with rapidity close to that of incident nuclei. Hyperfine Structure ( accuracy?): Production of different types of produced particles, etc.

5. From the lowest to the highest energies studied, important changes occur in the system created in the collision yet the number of final particles produced in any element of longitudinal phase space seems to be determined by the early stages of the collision process Is the simplicity seen in the data trivial? Is nature trying to give us some important clues? I am convinced that any correct theoretical description of AA collisions will automatically contain the basic features described above. They will not be the consequence of detailed calculations or accidents.

6. SHAPE OF dN/dy

7. Warning: rapidity y  pseudorapidity  change of reference frame: ⇏ Approximation = y is good provided that p>>m and  >>

8. NA5 DeMarzo, et al (1984) E178 From D. Chaney From Whitmore review

9. Is there a boost invariant central plateau? E895 E895 E895 BRAHMS prel. NA49 NA49 dN/dh AuAu UA5 / CDF 19.6 GeV 130 GeV 200 GeV PHOBOS dN/dh  Boost-invariance? 4GeV AuAu 6GeV AuAu 8GeV AuAu 40GeV PbPb 158GeV PbPb 200GeV AuAu Compiled by Gunther Roland Compiled by Peter Steinberg

10. At first glance both pA and dA seem to be very different Preliminary E178: pA data 19.6 GeV 13.7 GeV √SNN=9.7 GeV Data for different  (=Npart-1)

11. PHOBOS Multiplicity Detector Phobos @ RHIC E178 @ Fermilab: “Phobos 1” E178: Busza, Acta Phys. Pol. B8 (1977) 333 Elias et al, Phys. Rev. D 22 (1980)13

12. Unexpected long range correlations Brick et al. pAu 200GeV(lab) 200 GeV h-Emulsion (lab)

13. ENERGYDEPENDENCE

14. PHOBOS 200 GeV Brenner et al The appropriate energy for pp, pA and dA is approximately 2√SNN In pp collisions, on average, approximately half the energy goes into the leading baryon

15. Compiled by Peter Steinberg e-e+ and AA have same energy dependence

16. Energy dependence of particle production “Limiting fragmentation” Collision viewed in rest frame of CM: PHOBOS 19.6 GeV 130 GeV PHOBOS 200 GeV PHOBOS AuAu AuAu  Collision viewed in rest frame of one nucleus: PHOBOS Au+Au p + p dNch/dh ¢/<Npart>/2 dN/dh¢ 6% central UA5

17. “Limiting Fragmentation” in pA and dA PHOBOS

18. PHOBOS Why overlap region grows with energy? Is it evidence of saturation? (imagine RHIC with asymmetric energy collisions) (Can CGC be relevant at 6.7GeV?)

19. Elliptic flow: Directed flow: Phobos preliminary NA49 Compiled by Steve Manly Flow related to particle density!

20. INCIDENT SYSTEM (CENTRALITY) DEPENDENCE

21. Amazing Npart scaling for , K, p, d-A collisions for √SNN between 10 and 200 GeV Constant Each participant pair adds Npp. Gains at low h = losses at high h

22. Compiled by Rachid Nouicer

23. Why Npart (=+1) is such a relevant parameter in all regions of rapidity and at all energies? hA, √SNN 10 to 20 GeV p K+ + E178 E178 Radius ~ A1/3 Npart= 7 Ncoll.= 10 Nquarks +gluons = ? Why the following is equivalent to the above? E178 inel ~ (R1+R2)2 ~ (A11/3 + A21/3)2 ~ A2/3 Npart ~ A2/3(A11/3+ A21/3) ~ A Ncoll ~ A2/3(A11/3 * A21/3) ~ A4/3 Hadron cross section for first collision, meson cross section subsequently

24. Fine structure of centrality dependence 200 GeV Phobos Centrality Dependence at |h| < 1 central 260GeV pp 130 GeV peripheral 130 GeV PHOBOS AuAu 19.6 GeV p + p dN/dh¢ 6% central dNch/dh ¢/<Npart>/2 UA5 PHOBOS Au+Au

25. Particle quenching in the top two units of rapidity central pA pi-X peripheral Pt=0.3GeV/c 100GeV(lab) 130 GeV PHOBOS 200GeV(lab) pA pX Pt=0.3GeV/c XF y -2 -1 0 Brick et al. From Barton et al Phys Rev 27 (1983)2580

26. A of pA hX Barton et al Skupic et al Barton et al -2 -1 0 y

27. What I see in the multiparticle production data Same features occur in e+e-, pp, pA, dA and AA from 10 to 200GeV For all systems, at all energies, the features can be described in terms of a few simple rules Npart is a key parameter Considering that we are certainly passing through very different intermediate states, the similarity of the features in e+e-, pp, pA, dA, and AA is intriguiging, it suggests that the number of final particles produced in any element of longitudinal phase space is determined by the early stages of the collision process Expanding “fragmentation region” clearly shows something is saturating Strongly interacting matter seems to be remarkably “black” to fast partons. I am convinced that any correct theoretical description of AA collisions will automatically contain the basic features described in this talk. They will not be the consequences of detailed calculations or accidents.

28. For center of mass energies >10GeV Structure (<20% accuracy): Multiplicities and rapidity distributions in e+e-, pp, pA and AA are the same provided one takes the appropriate normalization and the appropriate energy. - the approriate normalization for symmetric collisions is Npart/2 and for asymmetric ones it is a linear function of rapidity, at each end proportional to the number of incident participants. - the appropriate energy is the same for e+e- and AA (√SNN ), and for pp, pA and dA it is approximately 2 √SNN . 2. The basic structure of dn/dy is approximately a gaussian, whose growth with energy is primarily determined by an ever increasing “limiting fragmentation region” (related to the increase of the rapidity of the incident particles) - You can find a discussion of some of the data presented here on Phobos WEB-site: www.phobos.bnl.gov/Publications/Proceedings/phobos_proceedings_publications.htm

29. SPARES

30. Is the importance of Npart accidental? A: A: + Emulsion From review by Fredriksson et al

31. Mechanism of rapidity loss of baryons in AA and pA are similar: From W.B & A.S. Goldhaber AuAu In pPb and AuAu ybaryons2 units BRAHMS, nucl-ex/0312023