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

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

Bottom line, for center of mass energies >10GeV: Structure (<20% accuracy): 1.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 (√S NN ), and for pp, pA and dA it is approximately 2 √S NN. 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) -

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) 2. 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.

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.

SHAPE OF dN/dy

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

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

Boost-invariance? E895 BRAHMS prel. NA49 Compiled by Gunther Roland dN/d  19.6 GeV130 GeV200 GeV PHOBOS  Is there a boost invariant central plateau? UA5 / CDF dN/d  AuAu 4GeV AuAu 6GeV AuAu 8GeV AuAu 40GeV PbPb 158GeV PbPb 200GeV AuAu Compiled by Peter Steinberg

E178: pA data Data for different (=N part -1) Preliminary √S NN =9.7 GeV At first glance both pA and dA seem to be very different 13.7 GeV 19.6 GeV

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

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

ENERGY DEPENDENCE

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

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

 PHOBOS Au+Au dN ch /d  / /2 6% central p + p dN/d  UA5 Collision viewed in rest frame of CM: 19.6 GeV130 GeV200 GeVPHOBOS Collision viewed in rest frame of one nucleus: Energy dependence of particle production “Limiting fragmentation” AuAu

“Limiting Fragmentation” in pA and dA 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?) PHOBOS

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

INCIDENT SYSTEM (CENTRALITY) DEPENDENCE

Amazing N part scaling for , K, p, d-A collisions for √S NN between 10 and 200 GeV Constant Each participant pair adds N pp. Gains at low  losses at high 

Compiled by Rachid Nouicer

E178 p K+K+ ++ N part = 7 N coll. = 10 N quarks +gluons = ?  inel ~ (R 1 +R 2 ) 2 ~ (A 1 1/3 + A 2 1/3 ) 2 ~ A 2/3 N part ~ A 2/3 (A 1 1/3 + A 2 1/3 ) ~ A N coll ~ A 2/3 (A 1 1/3 * A 2 1/3 ) ~ A 4/3 Why the following is equivalent to the above? Why N part (= +1) is such a relevant parameter in all regions of rapidity and at all energies? hA, √S NN 10 to 20 GeV Radius ~ A 1/3 Hadron cross section for first collision, meson cross section subsequently

PHOBOS Au+Au dN ch /d  / /2 6% central p + p dN/d  UA5 Fine structure of centrality dependence central peripheral 130 GeV PHOBOS AuAu 260GeV pp 200 GeV 130 GeV 19.6 GeV Phobos Centrality Dependence at |  < 1

Particle quenching in the top two units of rapidity From Barton et al Phys Rev 27 (1983)2580 pA pX pA pi-X XFyXFy -20 P t =0.3GeV/c 100GeV(lab) P t =0.3GeV/c central peripheral 130 GeV PHOBOS Brick et al. 200GeV(lab)

A  of pA  hX Barton et al Skupic et al y

What I see in the multiparticle production data 1.Same features occur in e + e -, pp, pA, dA and AA from 10 to 200GeV 2.For all systems, at all energies, the features can be described in terms of a few simple rules 3.Npart is a key parameter 4.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 5.Expanding “fragmentation region” clearly shows something is saturating 6.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.

For center of mass energies >10GeV Structure (<20% accuracy): 1.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 (√S NN ), and for pp, pA and dA it is approximately 2 √S NN. 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:

SPARES

Is the importance of N part accidental?  A: A: From review by Fredriksson et al + Emulsion

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