# Presentation: 369582

## 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

## Structure (<20% accuracy):

**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)
-               -

## 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.

## 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  >>

## E178

- NA5 DeMarzo, et al (1984)

- From D. Chaney

- From Whitmore review, NAL-Pub 73/70 (1973)

- E178 see:
- W.Busza, Acta Phys. Pol. B8 (1977) 333
- J.E.Elias et al., Phys.Rev.D22(1980) 13
- W.Busza Nuclear Physics A418 (1984)635c-645c

**Notes:**
J Whitmore December 1973
Busza Nuclear Physics A418 (1984)635c-645c
Busza, Acta Phys. Pol. B8 (1977) 333

## Boost-invariance?

- Compiled by Gunther Roland

- dN/d

**19.6 GeV**

**130 GeV**

**200 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

**Notes:**
UA5, ZPC 33 (1986) / CDF, PRD 41 (1990)

## At first glance both pA and dA seem to be very different

- E178: pA data

- Data for different  (=Npart-1)

- √SNN=9.7 GeV

- 13.7 GeV

- 19.6 GeV

**Notes:**
E178: Busza Acta Physica Polonica B8 (1977) 333

## PHOBOS Multiplicity Detector

- E178 @ Fermilab: “Phobos 1”

- Phobos @ RHIC

- E178: Busza, Acta Phys. Pol. B8 (1977) 333
-           Elias et al, Phys. Rev. D 22 (1980)13

## Unexpected long range correlations

- 200 GeV

- (lab)

- pAu 200GeV(lab)

- Brick et al.

- h-Emulsion

**Unexpected long range correlations**

**Notes:**
Brick et al
Proton+Emulsion data
W. Busza review 1976(Acta Phys. Pol. B8, 333)

##      ENERGYDEPENDENCE

## The appropriate energy for pp, pA and dA is approximately 2√SNN

- A.Brenner et a., Phys.Rev.D26 (1982) 1497l

- 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**

##  e-e+ and AA have same energy dependence

-  e-e+ and AA have same energy dependence

- 

** **

**PHOBOS Au+Au**

**dN****ch****/d********/<N****part****>/2**

**6% central**

**p + p  **

**dN/d******

- UA5

- Collision viewed in rest frame of CM:

**19.6 GeV**

**130 GeV**

**200 GeV**

**PHOBOS**

**PHOBOS**

**PHOBOS**

- Collision viewed in rest frame of one nucleus:

- Energy dependence of particle production
- “Limiting fragmentation”

**AuAu**

**AuAu**

## “Limiting Fragmentation” in pA and dA

- “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 Npart scaling for , K, p, d-A collisions for √SNN between 10 and 200 GeV

- 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 losses at high 

- E178:  W.Busza, Acta Phys. Pol. B8 (1977) 333
-           J.E.Elias et al, Phys. Rev. D 22 (1980)13

## Compiled by Rachid Nouicer

## Why Npart (=+1) is such a relevant parameter in all regions of rapidity and at all energies?

- E178

- E178

- E178

- p

- K+

- +

- Npart= 7
- Ncoll.= 10
- Nquarks +gluons = ?

-  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

- Why the following is equivalent to the above?

- Why Npart (=+1) is such a relevant parameter in all regions of rapidity and at all energies?

- hA, √SNN 10 to 20 GeV

- Radius ~ A1/3

- Hadron cross section for first collision, meson cross section subsequently

**Notes:**
E178 :Busza et al., PRL 41(1978).285

** **

**PHOBOS Au+Au**

**dN****ch****/d********/<N****part****>/2**

**6% central**

**p + p  **

**dN/d******

- UA5

- Fine structure of centrality dependence

**Notes:**
Au+Au nucl-ex/0301017d+Au & p+p preliminary

## Particle quenching in the top two units of rapidity

- From E451:Barton et al Phys Rev 27 (1983)2580

**pA      pX **

**pA     pi-X**

**X****F**
**y**

- -2

- -1

- 0

- Pt=0.3GeV/c
- 100GeV(lab)

- Pt=0.3GeV/c

**central**

**peripheral**

- 130 GeV  PHOBOS** **

- Brick et al.

- 200GeV(lab)

## A   of pA hX

- A   of pA hX

- Barton et al

- Skupic et al

-                   -2      -1                         0    y

- From E451:Barton et al Phys Rev 27 (1983) 2580

**Notes:**
Busza Nuclear Physics A544(1992)49c-64c
Busza Nuclear Physics A544(1992)49c-64c
PHOBOS, nucl-ex/0302015
Skupic et al Phys Rev D 18 (1978)3115

## 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.

- 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.

## Structure (<20% accuracy):

**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