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

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Structure and Fine Structure seen in ee-, pp,
pA and AA Multiparticle Production
BNL workshop, May 2004

• Wit Busza
• MIT

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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
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Bottom line, for center of mass energies gt10GeV
Structure (lt20 accuracy)

• Multiplicities and rapidity distributions in
  ee-, 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 (vSNN ), and for pp, pA and dA
  it is approximately 2 vSNN .
• 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)
• -

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Fine Structure (lt10 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.
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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.
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SHAPE OF dN/dy
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Warning rapidity y ? pseudorapidity ? change
of reference frame ?
?Approximation ? y is good provided
that pgtgtm and ?? gtgt
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NA5 DeMarzo, et al (1984)
E178
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
From D. Chaney
From Whitmore review, NAL-Pub 73/70 (1973)
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Is there a boost invariant central plateau?
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
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At first glance both pA and dA seem to be very
different
E178 pA data
19.6 GeV
13.7 GeV
vSNN9.7 GeV
Data for different ? (Npart-1)
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PHOBOS Multiplicity Detector
Phobos _at_ RHIC
E178 _at_ Fermilab Phobos 1
E178 Busza, Acta Phys. Pol. B8 (1977) 333
Elias et al, Phys. Rev. D 22 (1980)13
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Unexpected long range correlations
Brick et al.
pAu 200GeV(lab)
200 GeV
h-Emulsion
(lab)
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ENERGYDEPENDENCE
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The appropriate energy for pp, pA and dA is
approximately 2vSNN
In pp collisions, on average, approximately half
the energy goes into the leading baryon
A.Brenner et a., Phys.Rev.D26 (1982) 1497l
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e-e and AA have same energy dependence
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Energy dependence of particle production Limiting
fragmentation

Collision viewed in rest frame of CM
19.6 GeV
130 GeV
200 GeV
PHOBOS
PHOBOS
PHOBOS
AuAu
AuAu
?
Collision viewed in rest frame of one nucleus
PHOBOS AuAu
p p
dNch/dh /ltNpartgt/2
dN/dh
6 central
UA5

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Limiting Fragmentation in pA and dA
PHOBOS
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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?)
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Directed flow
Elliptic flow
Phobos preliminary
NA49
Compiled by Steve Manly
Flow related to particle density!
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INCIDENT SYSTEM (CENTRALITY) DEPENDENCE
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Amazing Npart scaling for ?, K, p, d-A collisions
for vSNN between 10 and 200 GeV
Constant
Each participant pair adds Npp . Gains at low h
losses at high h
E178 W.Busza, Acta Phys. Pol. B8 (1977) 333
J.E.Elias et al, Phys. Rev. D 22 (1980)13
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Compiled by Rachid Nouicer
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Why Npart (?1) is such a relevant parameter in
all regions of rapidity and at all energies?
hA, vSNN 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 (R1R2)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
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Fine structure of centrality dependence
p p
dN/dh
6 central
dNch/dh /ltNpartgt/2
UA5

PHOBOS AuAu
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Particle quenching in the top two units of
rapidity
central
pA pi-X
peripheral
Pt0.3GeV/c 100GeV(lab)
130 GeV PHOBOS
200GeV(lab)
pA pX
Pt0.3GeV/c
XF y
-2
-1
0
Brick et al.
From E451Barton et al Phys Rev 27 (1983)2580
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A? of pA ?hX
Barton et al
Skupic et al
From E451Barton et al Phys Rev 27 (1983) 2580
-2 -1
0 y
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• What I see in the multiparticle production data
• Same features occur in ee-, 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 ee-, 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.

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For center of mass energies gt10GeV
Structure (lt20 accuracy)

• Multiplicities and rapidity distributions in
  ee-, 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 (vSNN ), and for pp, pA and
  dA it is approximately 2 vSNN .
• 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