Global Observations from PHOBOS A story of scaling

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Global Observations from PHOBOSA story of
scaling
Mark D. Baker Brookhaven National Laboratory
for the Collaboration 8th
International Wigner Symposium May 28, 2003
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Collaboration (May 2003)
Birger Back, Mark Baker, Maarten Ballintijn,
Donald Barton, Bruce Becker, Russell Betts,
Abigail Bickley, Richard Bindel, Andrzej
Budzanowski, Wit Busza (Spokesperson), Alan
Carroll, Patrick Decowski, Edmundo Garcia,
Tomasz Gburek, Nigel George, Kristjan
Gulbrandsen, Stephen Gushue, Clive Halliwell,
Joshua Hamblen, Adam Harrington, Conor Henderson,
David Hofman, Richard Hollis, Roman Holynski,
Burt Holzman, Aneta Iordanova, Erik Johnson, Jay
Kane, Nazim Khan, Piotr Kulinich, Chia Ming Kuo,
Jang Woo Lee, Willis Lin, Steven Manly, Alice
Mignerey, Gerrit van Nieuwenhuizen, Aaron Noell,
Rachid Nouicer, Andrzej Olszewski, Robert Pak,
Inkyu Park, Heinz Pernegger, Corey Reed, Louis
Remsberg, Christof Roland, Gunther Roland, Joe
Sagerer, Pradeep Sarin, Pawel Sawicki, Iouri
Sedykh, Wojtek Skulski, Chadd Smith, Peter
Steinberg, George Stephans, Andrei Sukhanov, Ray
Teng, Marguerite Belt Tonjes, Adam Trzupek,
Carla Vale, Robin Verdier, Gábor Veres, Bernard
Wadsworth, Frank Wolfs, Barbara Wosiek,
Krzysztof Wozniak, Alan Wuosmaa, Bolek Wyslouch,
Jinlong Zhang ARGONNE NATIONAL
LABORATORY BROOKHAVEN NATIONAL LABORATORY INSTITU
TE 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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PHOBOS Detector in 2002
12m Be Beampipe
ZDC
ZDC
ZDC
1m
ZDC
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Extensive systematic data set
Phys. Rev. Lett. (2003), in press,
arXivnucl-ex/0210015
200 GeV
19.6 GeV
130 GeV
PHOBOS
PHOBOS
PHOBOS
dN/dh
Typical systematic band
(90C.L.)
h
h
h

• d2N/dhdf over 11 x 2p units of hx f
• AuAu at ?s19.6, (56), 130, 200 GeV
• pp and dAu on the way

f
h
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Scaling of rare (hard) processes
A
LA1/3
Ncoll of NN collisions A4/3 (formally
Glauber TAA(b)) Npart/2 of participating
nucleons A
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Midrapidity charged particle production
AuAu
200 GeV
hlt1
130 GeV
Preliminary 19.6 GeV
Collision scaling does NOT disappear at low
energy. Problem for naïve minijet based models.
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Initial state parton saturation?
QM2002 nucl-ex/0212009
200 GeV
130 GeV
Preliminary 19.6 GeV
Kharzeev, Levin, Nardi, hep-ph/0111315
l0.25 from fits to HERA data
xG(x)x-l Describes energy dependence
correctly!
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Parton Saturation describes AA
Kharzeev Levin, Phys. Lett. B523 (2001) 79
Same l (From HERA) describes dN/dh shape
correctly! ( energy centrality dep.)
PRL 87 (2001)
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Energy Dependence of Central dN/dh
Phys. Rev. Lett. (2003), in press,
arXivnucl-ex/0210015
Scale by Npart/2 shift to hh- ybeam
PHOBOS AuAu
dNch/dh
dNch/dh /ltNpartgt
6 central
PHOBOS AuAu
Systematic errors not shown
The fragmentation region extent grows with ?sNN
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xF scaling in AuAu
UA5, Z.Phys.C33, 1 (1986)
p p inel.
dNch/dh /ltNpartgt
6 central
dN/dh
PHOBOS AuAu
19.6 GeV is preliminary
Systematic errors not shown
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?Nch? scales with Npart
ee-
ee-
Error bands due to high-h extrapolation
AuAu
ee-
nucl-ex/0301017
(preliminary)
Total charged particle production Npart
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AA and ee- similar in shape as well as magnitude
200 GeV
ee- measures dN/dyT(rapidity relative
tothrust axis)
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Comparison of áNchñ vs. Energy
nucl-ex/0301017
pQCD ee- Calculation
? nucl-ex/0301017 Submitted for Publication
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Comparison of áNchñ vs. Energy
PHOBOS Preliminary Central AuAu
ee-
pp (pp) data _at_ ?seff
Central AA

• Different systems converge
• at high energy.

nucl-ex/0301017
1 10 102 103
?s (GeV)
Universality?
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PT Distribution of Charged Particles
AuAu
Phobos Preliminary
Systematic Errors not shown
? Phobos measures from pT, 0.030 5 GeV/c
beyond
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Comparing AuAu spectra to pp
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Ratio of AuAu and pp spectra at 200 GeV
mid-peripheral

• High pT hadrons dont scale like Ncoll either!

Npart 65 4
Npart 344 12
central
arXivnucl-ex/0302015
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A-dependence of Charged Spectra

• Normalize by ltNpartgt/2
• Divide by the value at Npart65

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Normalize by Npart/2. Divide by the value at
Npart65
Collision scaling would imply
PHOBOS
nucl-ex/0301017
AuAu 200 GeV
UA1 pp (200 GeV)
Particle Production Scales with Nparteven at
high pT
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Approximate Npart scaling at high pT is MAXIMAL
suppression!
Ncoll S / V Npart4/3 / L Npart
Only hadrons produced on the surface survive!
NOTE Very peripheral collisions should recover
Ncoll scaling
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Is final state jet quenching the only
explanation?
Kharzeev, Levin, McLerran hep-ph/0210332
Particle Yield/ltNpart/2gt
Initial state parton saturation works too ...
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How do we resolve this?

• Strong (maximal) final state suppression at high
  pT?
• Indication of high density strongly interacting
  matter!
• Strong initial state suppression persisting to
  moderately high pT?
• Indication of multipartonic effects in the
  nuclear wavefunction!

dAu data! Prediction Saturation RdAu 0.75
for 15 central dAu
Kharzeev, Levin, Nardi hep-ph/0212316
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Centrality determination in dAu
HIJING dAu MC
HIJING dAu MC
Centrality in dAu Handle with care!
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Preliminary Results from dAu
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Preliminary Results from dAu
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Preliminary Results from dAu
KLN Saturation
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Global Observations from PHOBOS

• Empirical Scaling Rules
• Overall particle production in AuAu (low pT)
• Hard component does not grow with energy.
• Limiting fragmentation (xF scaling) seen in
  AuAu.
• Overall particle production scales like Npart
• Particle production/participant pair looks like
  ee-
• Behavior at moderately high pT
• Maximal suppression from Ncoll scaling in AuAu.
• Ncoll scaling (or slight enhancement) in dAu
• Centrality dependence in dAu
• Ncoll scaling even for 20 most central data!
• Increasing suppression from Ncoll scaling at low
  pT

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Conclusions

• PHOBOS scaling rules provide many pieces of the
  puzzle.
• The latest news from PHOBOS
• We have compared central AuAu to central dAu.
• This data strongly disfavors the initial state
  parton saturation interpretation of high pT
  hadron suppression.

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Backup slides
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This Year PHOBOS Detector 2003
mini-pCal
SPECTRIG
? Moved TOF walls back 5 m from interaction
point
? Installed new spectrometer trigger detector
that selects on high pT tracks
pCal
? Installed new time-zero (T0) Cerenkov
detectors to provide triggering and on-line
vertexing as well as a start time for our TOF
walls.
? Proton calorimeter on Gold and Deuteron going
sides for dA run
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Initial state parton saturation?
See Iancu, Leonidov, McLerran hep-ph/0202270

• Gluon density cannot grow indefinitely.
• Non-Abelian diagram gg?g kicks in at
  low x or low k?.

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Centrality scaling in pT bins (AuAu)

• Spectra normalized to a fit at mid-peripheral
  45-50 bin.

? Over the centrality range studied, for low and
high pT, the AuAu data scale approximately with
number of participants.
? nucl-ex/0302015 Submitted for Publication
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Spectrometer Performance
Acceptance
Momentum Resolution

• Data Sample Production Run 2001(200 GeV)
• 7.8 M AuAu Events, Min. Bias Trigger
• 32 M reconstructed particles

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Centrality Determination (AuAu)
Data
HIJING GEANT Glauber calculation Model of
paddle trigger
Paddle signal
DataMC
Nparticipants
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PHOBOS Preliminary Results from dA
PHOBOSpreliminary
PHOBOS preliminary
RdAu
RdAu
PHOBOS preliminary
PHOBOS preliminary
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Remove the Leading Proton Effect
?s
?seff
Basile et al (1980-1984)
pQCD ee- Calculation
(A. Mueller, 1983)
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Many ways to slice pz
Rapidity Generalized velocity
Feynman x scaled pz
Pseudorapidity y easier to measure