Bulk Observables in p-p, d-Au and Au-Au at RHIC

1
Bulk Observables in p-p, d-Au and Au-Au at RHIC

• David Hofman
• University of Illinois at Chicago
• For the Collaboration

QCD and High Energy Hadronic InteractionsMarch
28 April 4, 2004 XXXIXth Recontres de Moriond
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Collaboration (February 2004)
Birger Back, Mark Baker, Maarten Ballintijn,
Donald Barton, Russell Betts, Abigail Bickley,
Richard Bindel, Wit Busza (Spokesperson), Alan
Carroll, Zhengwei Chai, Patrick Decowski,
Edmundo García, Tomasz Gburek, Nigel George,
Kristjan Gulbrandsen, Clive Halliwell, Joshua
Hamblen, Adam Harrington, Michael Hauer, Conor
Henderson, David Hofman, Richard Hollis, Roman
Holynski, Burt Holzman, Aneta Iordanova, Jay
Kane, Nazim Khan, Piotr Kulinich, Chia Ming Kuo,
Willis Lin, Steven Manly, Alice Mignerey, Gerrit
van Nieuwenhuizen, Rachid Nouicer, Andrzej
Olszewski, Robert Pak, Inkyu Park, Heinz
Pernegger, Corey Reed, Michael Ricci, Christof
Roland, Gunther Roland, Joe Sagerer, Helen Seals,
Iouri Sedykh, Wojtek Skulski, Chadd Smith,
Maciej Stankiewicz, Peter Steinberg, George
Stephans, Andrei Sukhanov, Marguerite Belt
Tonjes, Adam Trzupek, Carla Vale, Siarhei
Vaurynovich, Robin Verdier, Gábor Veres, Edward
Wenger, Frank Wolfs, Barbara Wosiek, Krzysztof
Wozniak, Alan Wuosmaa, Bolek Wyslouch ARGONNE
NATIONAL LABORATORY BROOKHAVEN NATIONAL
LABORATORY INSTITUTE OF NUCLEAR PHYSICS,
KRAKOW MASSACHUSETTS INSTITUTE OF
TECHNOLOGY NATIONAL CENTRAL UNIVERSITY,
TAIWAN UNIVERSITY OF ILLINOIS AT
CHICAGO UNIVERSITY OF MARYLAND UNIVERSITY OF
ROCHESTER
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Charged Particle Production at RHIC
Pseudorapidity ? Lorentz invariant angle with
respect to the beampipe
h-ln tan q/2
0
-1
1
-2
2
3
-3
Beamline
not to scale
4
A coffee napkin Estimate ofEnergy Density at
Midrapidity.
Look at all produced particles in a Central
Head-on Collision
Dh 1
Total energy released in Dh1 is 1000 GeV
Max initial overlap volume
? Initial Energy Density Estimate, e 5 GeV/fm3
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Charged Particle Density near Midrapidity
Central Collisions (for Heavy Ion data)
RHIC - combined
vsNN (GeV)
? Logarithmic Rise for AA data, above pp
baseline
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PHOBOS Bulk Observables Low pT
PHOBOS
arXivnucl-ex/0401006
Systematic Errors not shown
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Participant Scaling
AuAu Collisions
p p Collisions
of participating pairs of nucleons Npart/2
Npart/2 1
Npart/2 A
Binary Collision Scaling
of binary NN collisions Ncoll
LA1/3
Ncoll 1
Ncoll A4/3
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Centrality Dependence of Midrapidity Charged
Particle Yields
20
200 GeV - hlt1
Binary Collision(Ncoll) Scaling
dN/dh/(Npart/2)
10
AuAu
pp
Participant (Npart) Scaling
0
0
200
400
ltNpartgt
peripheral
central
? AuAu Centrality Dependence allows only about
10 Ncoll Scaling
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Charged Particle Production at Midrapidity
Energy and Centrality Dependence
Data is normalized by pp value for each energy.
Binary collision scaling
200 GeV
AuAu
130 GeV
19.6 GeV preliminary
Participant scaling
peripheral
central
? All RHIC energies show a similar Npart
dependence
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Ratios to Help Cancel Systematics
Systematics
PHOBOS, PRC 65, 061901(R) (2002)
50
40
30
20
10
0
Percentile of Cross Section

• Systematics Dominated by Trigger
  Efficiency/Centrality Determination

Ratio (200/130) 1.14 0.01 (stat) 0.05 (syst)
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Centrality Dependence of Total Charged Particle
Production ?Nch?
AuAu Collisions
central
200 GeV
dN/dh/lt1/2 Npartgt
peripheral
central
peripheral
19.6 GeV
Pseudorapidity

• Nch(AuAu) (Npart/2) Nch(ee-)

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Pseudorapidity Distribution of Charged Particles
in d Au and p p Collisions at 200 GeV

• p p at 200 GeV

• d Au at 200 GeV Min-Bias

arXivnucl-ex/0311009 andSubmitted to PRL
PHOBOS Preliminary

• PHOBOS can measure down to very low
  multiplicities.

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dAu Centrality Dependence of dNch/dh Shape
(Normalized to Nch so can compare shape change)
?Npart?
(15.5)
(10.8)
(7.2)
(4.2)
Lines to Guide Eye Only
Systematic errors not shown
(2.7)

• In dAu, particle production shifts to negative
  rapidity with increasing Npart.

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Participant Scaling in dAu

• Nch(dAu) (Npart/2) Nch(pp)

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?Nch? in Au-Au vs. p-p and d-Au _at_ 200 GeV
AuAu
ee-
? Difference in total charged particle production
between AuAu (ee-) vs. dAu (pp) at same
collision energy
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Features of the Data at High Pseudorapidity (h).
? Move to rest frame of one nucleus i.e. h h
ybeam.
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Reminder Limiting Fragmentation in pp
Ansatz Benecke, Chou, Yang, Yen, Phys. Rev.
188, 2159 (1969)
Data UA5 (Alner et al.), Z.Phys.C33, 1 (1986)
? Ansatz At high collision energy, d2N/dydpT
and particle mix, reach a limiting value and
become independent of energy around beam rapidity.
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Limiting Fragmentation in AuAu
? Growth of the Fragmentation Region with ?sNN
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Limiting Fragmentation in dAu and pEmulsion Data
dAu pEmulsion per incident nucleon and approx.
same Npart
Npart Selection
p
Em
1
2.4
d
Au
1.6x2.4
1.6
? Growth of the Fragmentation Region with ?sNN in
dAu and pEm
R. Nouicer, QM 04
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Charged Particle Flow A Bulk Collective Effect
Initial spatial anisotropy
z
z
Reaction plane (YR)
y
f
x
y
y
x
x (defines YR)
Final momentum anisotropy
py
dN/d(f -YR ) N0 (1 2v1cos (f-YR)
2v2cos (2(f-YR)) ... )
px
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Directed Flow (v1) In Beam Rest Frame
In target frame of reference, directed flow
exhibits signal consistent with limiting
fragmentation
? Limiting Fragmentation Behavior in Directed Flow
S. Manley, 20th Winter Workshop
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Elliptic Flow (v2) In Beam Rest Frame
v2
PHOBOS Preliminary v2200
PHOBOS v2130
h
? Limiting Fragmentation Behavior in Elliptic Flow
S. Manley, 20th Winter Workshop
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Experimental SummaryBulk (charged particle)
Observables at RHIC

• Scaling of multiplicity data with Npart/2 in
  AuAu and dAu.
• Per participant pair, AuAu reaches ee- total
  particle production level at RHIC energies. dAu
  reaches pp level (at the same collision energy).
• Limiting fragmentation of charged particle
  multiplicity yields (dN/dh) observed in AuAu and
  dAu at RHIC.
• Limiting fragmentation of azimuthal angular
  distribution of charged particles (v1 and v2)
  observed at RHIC.