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

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 (√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)

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 >>

€

′y ⇒ y + Δyrelative

€

′

€

+Δyrelative

€

−y = tanh−1 cosϑ − tanh−1 β

η − y = tanh−1 pl

p− tanh−1 pl

E

€

1

γ

NA5 DeMarzo, et al (1984)

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

E178

From D. ChaneyFrom 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

Boost-invariance?E895 E895 E895

BRAHMS

prel.

NA49 NA49

Compiled by Gunther Roland

dN/d

19.6 GeV 130 GeV 200 GeVPHOBOS

Is there a boost invariant central plateau?

UA5 / CDF

dN/d

€

p p

AuAu

4GeV AuAu

6GeV AuAu

8GeV AuAu

40GeV PbPb

158GeV PbPb

200GeV AuAu



Compiled by Peter Steinberg



E178: pA data

Data for different (=Npart-1)

Preliminary

√SNN=9.7 GeV

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

13.7 GeV 19.6 GeV

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



200 GeV€

R η( ) ≡

dn

dηpA or dA( )

dn

dηpp( )

(lab)

pAu 200GeV(lab)

Brick et al.

h-Emulsion

€

= Npart − 1( ) = 2.4

Unexpected long range correlations

ENERGYDEPENDENCE

PHOBOS 200 GeVPHOBOS 200 GeV

€

pp → pX ≡ pp → X

provided Mx2 is the same

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



)/exp( sBsch CAN αα=

Compiled by Peter Steinberg

e-e+ and AA have same energy dependence

PHOBOS Au+Au

dN

ch/d

′/

<N

par

t>/2 6% central

beamy−≡′

p + p

dN

/d′

UA5

beamy−≡′

Collision viewed in rest frame of CM:19.6 GeV 130 GeV 200 GeVPHOBOS PHOBOS PHOBOS

Collision viewed in rest frame of one nucleus:

Energy dependence of particle production“Limiting fragmentation”

AuAu AuAu

“Limiting Fragmentation” in pA and dAPHOBOS

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

€

Nch

N part

2 ⎛

⎝ ⎜

⎞

⎠ ⎟= Constant

€

Nchpp

Each participant pair adds Npp .

Gains at low losses at high

€

N chpp

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

Compiled by Rachid Nouicer

Phobos and E178 data

E178

E178

E178

p

K+

+

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

inel ~ (R1+R2)2 ~ (A11/3 + A2

1/3)2 ~ A2/3

Npart ~ A2/3(A11/3+ A2

1/3) ~ ANcoll ~ A2/3(A1

1/3 * 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

PHOBOS Au+Au

dN

ch/d

′/<

Np

art>

/2

6% central

beamy−≡′

p + p

dN

/d′

UA5

beamy−≡′

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

pA pX

pA pi-X

XF

y-2 -1 0

Pt=0.3GeV/c

100GeV(lab)

Pt=0.3GeV/c

central

peripheral

130 GeV PHOBOS

€

XF =Pl

Pinc



Brick et al.

200GeV(lab)



Aα of pA hXBarton et al Skupic et al

-2 -1 0 y

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

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 (√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

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

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