Transcript Charged Particle Multiplicities from Cu+Cu, Au+Au and d+Au Collisions at RHIC

Charged Particle
Multiplicities from
Cu+Cu, Au+Au and
d+Au Collisions at RHIC
Aneta Iordanova
University of Illinois at Chicago
for the
collaboration
Phobos Collaboration
Burak Alver, Birger Back, Mark Baker, Maarten Ballintijn, Donald Barton, Russell Betts, Richard Bindel,
Wit Busza (Spokesperson), Vasundhara Chetluru, Edmundo García, Tomasz Gburek, Joshua Hamblen,
Conor Henderson, David Hofman, Richard Hollis, Roman Hołyński, Burt Holzman, Aneta Iordanova,
Chia Ming Kuo, Wei Li, Willis Lin, Constantin Loizides, Steven Manly, Alice Mignerey,
Gerrit van Nieuwenhuizen, Rachid Nouicer, Andrzej Olszewski, Robert Pak, Corey Reed, Christof Roland,
Gunther Roland, Joe Sagerer, Peter Steinberg, George Stephans, Andrei Sukhanov,
Marguerite Belt Tonjes, Adam Trzupek, Sergei Vaurynovich, Robin Verdier, Gábor Veres, Peter Walters,
Edward Wenger, Frank Wolfs, Barbara Wosiek, Krzysztof Woźniak, Bolek Wysłouch
ARGONNE NATIONAL LABORATORY
INSTITUTE OF NUCLEAR PHYSICS PAN, KRAKOW
NATIONAL CENTRAL UNIVERSITY, TAIWAN
UNIVERSITY OF MARYLAND
DNP, Nashville, 28 Oct 2006
BROOKHAVEN NATIONAL LABORATORY
MASSACHUSETTS INSTITUTE OF TECHNOLOGY
UNIVERSITY OF ILLINOIS AT CHICAGO
UNIVERSITY OF ROCHESTER
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PHOBOS detector
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Outline
Control parameters of a heavy ion collision

Energy
19.6 - 200 GeV

Colliding system size
centrality Npart from 3.5 (d+Au) – 360 (Au+Au)

Species
p+p, d+Au, Cu+Cu and Au+Au
Global features of charged particle production
(observables)


dNch/dh shapes (particle distributions in h)
Mid-rapidity factorization
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Data
comparison of Au+Au and Cu+Cu
d+Au and p+p
Au+Au : PRL 91, 052303 (2003)
Au+Au : PRC 74, 021901 (2006)
d+Au : PRC 72, 031901 (2005)
dN/dh distribution
Charged hadron dNch/dh distribution
62.4 GeV
130 GeV
200 GeV
Cu+Cu data
Au+Au data
19.6 GeV
preliminary
With energy:


preliminary
d+Au
Height increases
Width increases (in h space)
With centrality(0-50% central):

Height increases
With species:
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2006
systematic trends
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dN/dh distribution
Comparison of Au+Au and Cu+Cu
200 GeV
For the same
collision system
size (Npart) dNch/dh
shape is very
similar for


Preliminary
15-25%, Npart = 61
Au+Au
45-55%, Npart = 56
central Cu+Cu with
mid-central Au+Au
collisions
mid-central Cu+Cu
with peripheral
Au+Au collisions
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midcentral
central
Cu+Cu
Cu+Cu
Preliminary
3-6%, Npart = 100
Au+Au
35-40%, Npart = 99
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dN/dh distribution
Comparison of Au+Au, d+Au and
p+p collisions at 200 GeV
Scale by Npart/2


allows for a direct
comparison to p+p
i.e. normalized to 1
participating pair
Multiplicity obtained at the
same center-of-mass
energy is similar in p+p
and d+Au
Multiplicity is larger for
Au+Au collisions at the
same energy
All at √s = 200 GeV
d+Au : PRL 93, 082301 (2004)
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d+Au : PRC 72, 031901 (2005)
p+p : 2004 J.Phys.G 30 S1133-1137
dN/dh distribution

PHOBOS d+Au and p+p
Data at √s = 200 GeV
3
Npart
More peripheral
collisions tend toward
p+p shape
2
More detailed
comparison of d+Au
and p+p shows
dNch
dη
Comparison of d+Au and p+p
2
1
0
-6
-4
-2
0
2
4
6
η
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factorization
at midrapidity
in energy and centrality
Au+Au : PRC 74, 021901 (2006)
Mid-rapidity factorization
Measured pseudorapidity density per
participant pair as a function of Npart
Mid-rapidity dNch/dh


PHOBOS
PHOBOS
Information about the
created matter
→energy density
Particle production in
A+A: interplay between
collision centrality
(geometry) and collision
energy?
balance of binary/soft
processes
Au+Au
Cu+Cu Au+Au
preliminary
0-50% cross-section
90 % C.L.
200 GeV (UA5)
19.6 and 62.4 GeV (ISR)
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Au+Au : PRC 74, 021901 (2006)
Mid-rapidity factorization
Midrapidity Ratios
Data ratio 200/X

no centrality (geometry)
dependence
HIJING
PHOBOS
Models

200/19.6
HIJING
200/62.4
disagrees with data

KLN
Saturation
Saturation Model
(KLN)
Cu+Cu
200/130
Au+Au
preliminary
flat centrality
dependence as in data
HIJING:Comput.Phys.Commun. 83 (1994) 307,v 1.35
KLN: Phys.Lett.B523 79 (2001) & arXiv:hep-ph/0111315
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factorization
at midrapidity
versus pT
pT factorization
Transverse Momentum
Factorization
So far discussed
factorization of bulk
matter

~pT<1GeV/c
Can look at
differential
factorization for pT
bins
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pT factorization
Transverse Momentum
Factorization
Ratio of charged hadron yields in 200 and 62.4 GeV

factorization up to pT ≈ 4 GeV/c for Npart > 40
<pT> = 0.25 GeV/c
<pT> = 1.25 GeV/c
<pT> = 2.5 GeV/c
<pT> = 3.38 GeV/c
<pT> = 3.88 GeV/c
Au+Au
Cu+Cu
Au+Au: PRL 94, 082304 (2005)
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Summary
PHOBOS has measured multiplicity for




large systematic dataset
-5.4<η<5.4
2 to 360 participants
√s = 19.6 to 200 GeV
Au+Au and Cu+Cu data are similar at the same Npart
Scaling and factorization properties are found in the Au+Au
data



extended longitudinal scaling
mid-rapidity factorization in bulk yield and versus pT
seem to persist into the Cu+Cu collision system
Observed factorization in energy and centrality is seen in
multiplicity and versus pT

implies that this is set at an early stage of the collision and is
connected with the geometry of the collision
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The End
pT factorization
Transverse Momentum
Factorization
Ratio of yield for 200 and 62.4 GeV is centrality
independent for all measured pT bins
Data from PRL 94, 082304 (2005)
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