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
Moriond 2004 2
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 Hołyński, 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 Woźniak, Alan Wuosmaa, Bolek Wysłouch
ARGONNE NATIONAL LABORATORY BROOKHAVEN NATIONAL LABORATORYINSTITUTE OF NUCLEAR PHYSICS, KRAKOW MASSACHUSETTS INSTITUTE OF TECHNOLOGY
NATIONAL CENTRAL UNIVERSITY, TAIWAN UNIVERSITY OF ILLINOIS AT CHICAGOUNIVERSITY OF MARYLAND UNIVERSITY OF ROCHESTER
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Charged Particle Production at RHIC
670d
ch
dN@ midrapidity 200 GeV
=-ln tan /2
Pseudorapidity = = Lorentz invariant angle with
respect to the beampipe
0-1
-2
-3
+1
+2+3
dN
ch/d
Central (head-on) Collisions
Beamlinenot to scale
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A “coffee napkin” Estimate ofEnergy Density at Midrapidity.
1000~all
d
dN
GeVE 1~
32 200~)1(~ fmfmRTotal energy released in =1 is ~ 1000 GeV
Initial Energy Density Estimate, ~ 5 GeV/fm3
Max initial overlap volume
Look at all produced particles in a Central ‘Head-on’ Collision = 1
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Charged Particle Density near Midrapidity
RHIC - combined
Central Collisions (for Heavy Ion data)
SPS RHICAGS
√sNN (GeV)
“Logarithmic Rise” for AA data, above pp baseline
Gluon Saturation
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Systematic Errors not shown
‘PHOBOS’ Bulk Observables ≡ Low pT
cGeVTpmeasures
ddN / 2"" general)in yields particle (charged
arXiv:nucl-ex/0401006
PHOBOS
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Ncoll = 1
Npart/2 = 1
“Participant” Scaling
Binary “Collision” Scaling
p + p Collisions Au+Au Collisions
Npart/2 ~ A
L~A1/3
Ncoll ~ A4/3
# of participating pairs of nucleons
≡ Npart/2
# of binary NN collisions
≡ Ncoll
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Centrality Dependence of Midrapidity Charged Particle Yields
Au+Au
0 200 4000
10
20
dN/d
/(N
pa
rt/2)
<Npart>
Au+Au Centrality Dependence allows only about 10% Ncoll Scaling
200 GeV - ||<1
peripheral central
p+p
Binary Collision(Ncoll) Scaling
Participant(Npart) Scaling
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All RHIC energies show a similar Npart dependence
Charged Particle Production at Midrapidity
19.6 GeV preliminary
130 GeV200 GeV
Data is normalized by p+p value for each energy.
Energy and Centrality Dependence
Au+Au
p + p
peripheral central
Participant scaling
Binary collision scaling
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Ratios to Help Cancel Systematics
Systematics Dominated by Trigger Efficiency/Centrality Determination
Systematics
Percentile of Cross Section50 40 30 20 10 0
PHOBOS, PRC 65, 061901(R) (2002)
Ratio (200/130) = 1.14 ± 0.01 (stat) ± 0.05 (syst)
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Centrality Dependence of Total Charged Particle Production Nch
Pseudorapidity
dN
/d/
<1/
2 N
par
t>
200 GeV
19.6 GeV
central
peripheral
central
peripheral
200 GeV
130 GeV
19.6 GeV
<Nch>e+e-*(Npart/2)
Au+Au Collisions
Nch(AuAu) = (Npart/2) Nch(e+e-)
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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
arXiv:nucl-ex/0311009 andSubmitted to PRL
PHOBOS Preliminary
PHOBOS can measure down to very low multiplicities.
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d+Au Centrality Dependence of dNch/d Shape
In dAu, particle production shifts to negative rapidity with increasing Npart.
Systematic errors not shown
(4.2)
(15.5)
(2.7)
(7.2)
(10.8)
(Normalized to Nch so can compare shape change)
Npart
peripheral
Lines to Guide Eye Only
central
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Participant Scaling in d+Au
Nch(dAu) = (Npart/2) Nch(pp)
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Nch in Au-Au vs. p-p and d-Au @ 200 GeV
Difference in total charged particle production between Au+Au (e+e-) vs. d+Au (pp) at same collision energy
e+e- Au+Au
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Features of the Data at High Pseudorapidity ().
PHOBOS Au+Au
dN
ch/d
→ Move to rest frame of one nucleus: i.e. ’ = – ybeam.
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Reminder: Limiting Fragmentation in p+p
Data: UA5 (Alner et al.),Z.Phys.C33, 1 (1986)
p + p inel.
dN
/d
beamy Ansatz: At high collision energy, d2N/dy’dpT and particle mix, reach a limiting value and become independent of energy around beam rapidity.
Ansatz: Benecke, Chou, Yang, Yen, Phys. Rev. 188, 2159 (1969)
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Limiting Fragmentation in Au+Au
Growth of the Fragmentation Region with sNN
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dAu & pEmulsion per incident nucleon and approx. same Npart
Npart Selection:
p Em
1 2.4
d Au
1.6x2.41.6
Limiting Fragmentation in dAu and pEmulsion Data
Growth of the Fragmentation Region with sNN in d+Au and pEm
R. Nouicer, QM ‘04
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Reaction plane
(R)
x
z
y
x
x (defines R)
y
zy
Charged Particle “Flow”: A Bulk Collective Effect
Initial spatial anisotropy
px
py
Final momentum anisotropy
dN/d(R ) = N0 (1 + 2v1cos (R) +
2v2cos (2(R)) + ... )
Elliptic Flow: v2
Directed Flow: v1
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In target frame of reference, directed flow exhibits signal consistent
with limiting fragmentation
Directed Flow (v1) In Beam Rest Frame
Limiting Fragmentation Behavior in Directed FlowS. Manley, 20th Winter Workshop
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PHOBOS Preliminary v2200
PHOBOS v2130
Elliptic Flow (v2) In Beam Rest Frame
S. Manley, 20th Winter Workshop
v2
Limiting Fragmentation Behavior in Elliptic Flow
’
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Experimental SummaryBulk (charged particle) Observables at RHIC
• Scaling of multiplicity data with Npart/2 in Au+Au and d+Au.
• Per participant pair, Au+Au reaches e+e- total particle production level at RHIC energies. d+Au reaches p+p level (at the same collision energy).
• “Limiting fragmentation” of charged particle multiplicity yields (dN/d) observed in Au+Au and d+Au at RHIC.
• “Limiting fragmentation” of azimuthal angular distribution of charged particles (v1 and v2) observed at RHIC.