Phobos data on dNdh

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Latest PHOBOS Results Bjorken is AWOL! Mark D.
Baker(BNL)for the Collaboration

• Phobos data on dN/dh
• New Phobos data on dN/dh
• Particle production in ppAA collisions
• The source isnt boost invariant
• dN/dh may teach us about QCD

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The PHOBOS Collaboration
Birger Back, Alan Wuosmaa Mark
Baker, Donald Barton, Alan Carroll, Nigel George,
Stephen Gushue, George Heintzelman, Burt Holzman,
Robert Pak, Louis Remsberg, Peter Steinberg,
Andrei Sukhanov Andrzej Budzanowski,
Roman Holynski, Jerzy Michalowski, Andrzej
Olszewski, Pawel Sawicki , Marek Stodulski, Adam
Trzupek, Barbara Wosiek, Krzysztof Wozniak
Wit Busza (Spokesperson), Patrick Decowski,
Kristjan Gulbrandsen, Conor Henderson, Jay Kane ,
Judith Katzy, Piotr Kulinich, Johannes
Muelmenstaedt, Heinz Pernegger, Corey Reed,
Christof Roland, Gunther Roland, Leslie
Rosenberg, Pradeep Sarin, Stephen Steadman,
George Stephans, Gerrit van Nieuwenhuizen, Carla
Vale, Robin Verdier, Bernard Wadsworth, Bolek
Wyslouch Chia Ming Kuo, Willis Lin, Jaw-Luen
Tang Joshua Hamblen , Erik Johnson, Nazim
Khan, Steven Manly,Inkyu Park, Wojtek Skulski,
Ray Teng, Frank Wolfs Russell Betts,
Edmundo Garcia, Clive Halliwell, David Hofman,
Richard Hollis, Aneta Iordanova, Wojtek Kucewicz,
Don McLeod, Rachid Nouicer, Michael Reuter, Joe
Sagerer Richard Bindel, Alice Mignerey
ARGONNE NATIONAL LABORATORY BROOKHAVEN NATIONAL
LABORATORY INSTITUTE OF NUCLEAR PHYSICS,
KRAKOW MASSACHUSETTS INSTITUTE OF
TECHNOLOGY NATIONAL CENTRAL UNIVERSITY,
TAIWAN UNIVERSITY OF ROCHESTER UNIVERSITY OF
ILLINOIS AT CHICAGO UNIVERSITY OF MARYLAND
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What do I mean Bjorken?
Boost-invariant
Increasing E
y
y
dN/dy
Inside-out 1 dimensional
0
yy-ybeam
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Impact of Bjorken
X

• dN/dy distribution is flat over a large region
  except near the target.
• v2 is independent of y over a large region except
  near the target. (2d-hydro.)
• pT(y) described by 1d or 2d-hydro.
• Usual HBT interpretation starts from a
  boost-invariant source.
• T(t) described by 1d-hydro.
• Simple energy density formula

X
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PHOBOS Apparatus
135,000 Silicon Pad channels
12 meters of Beryllium beampipe
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PHOBOS Silicon Detector
Octagon Detector
Vertex Detector
Octagon Detector 2.7 x 8.8 mm2 Vertex Detector
0.4 x 12 mm2
Ring Counter
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Many ways to slice pz
Rapidity Generalized velocity
Feynman x scaled pz
Pseudorapidity y easier to measure
Away from mid-rapidity
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Single Event in PHOBOS
An event in PHOBOS
Unrolled
tracklets
f
h
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PHOBOS results at 200 GeV
Theory 1999
Theory 2000
PHOBOS 2001
PHOBOS 2000
PRL 85 (2000) 3100
PRL 88 (2002) 022302
Total Ncharged 5000 particles
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RHIC results so far
PHOBOS, PRL 88 (2002) 022302
Brahms 200 GeV nucl-ex/0112001
Phenix 200 GeV preliminary
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Centrality Dependence
h lt 1
PRC 65, 031901(2002) submitted to PRC
Saturation Model Kharzeev,Levin nucl-th/0108006
Peripheral
Central
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Implications

• Particle production on the low side.
• Limited entropy production in late stages.
• dN/dh is a window to QCD

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2
3
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Colliding Nuclei
Parton Cascade
Hadron Gas Freeze-out
HardCollisions
QGP? / Fragmentation
Gentle Freeze-out
Geometry/Saturation
QCD
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Analog and Digital Hit-Counting
f
h
Analog
Digital

• Sum energy
• Divide by E/particle
• Correct for material

• Count hits
• Correct for multi-hits
• Correct for material

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Latest PHOBOS results
Typical Systematic Errors
200 GeV
130 GeV
dN/dh
dN/dh
dN/dh
Peripheral
h
h
h
dN/dh
dN/dh
dN/dh
Central
h
h
h
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Collider Kinematics
Beam rest frame S
Lab cm frame S
ybeam
-ybeam
y-2ybeam
y0
Fragmenting Target
p
ygt0
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Results Limiting Fragmentation
Latest PHOBOS results (vs pp)
UA5, Z.Phys.C33, 1 (1986)
p p inelastic
AA
PHOBOS 200 0-6 PHOBOS 130 0-6 EMU-13 17
0-9.4 (different frame)
Systematic errors not shown
AuAu and pp show the same behavior, the extent of
the fragmentation region grows with collision
energy
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Results Limiting Fragmentation vs Centrality
Centrality dependence.

• Each centrality exhibits limiting fragmentation
  (E-independence)
• but the shape in this region depends on
  centrality !

200 GeV
200 GeV
130 GeV
130 GeV
Fragmentation
Fragmentation
Systematic errors not shown
200 GeV Data
130 GeV Data
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Fragmentation Energy dependence
Low energy
ANY High energy
Confusion
Fragmenting Target
For EgtEthresh, dN/dy(y0) reaches a limiting
value.
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Lets pick a different frame...
Beam rest frame S
Arbitrary frame S
y-2ybeam
y0
y3
y3-2ybeam

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Makes sense for pp
p etc.
Limiting fragmentation could just be local
string fragmentation
Also works in ee-
But how about AA??
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Can we see the Limit Curves.
UA5, Z.Phys.C33, 1 (1986)
AA
p p inel.
Systematic errors not included
Line p to guide the eye
1.45 x line p
Systematic errors not shown
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Boost-invariance vs. Outside-in evolution
McLerran, Venugopolan Kharzeev, Nardi,
Levin Kovchegov...
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Can we calculate the limit curves?

• Saturated initial state gives predictions about
  final state.
• Nh c x Ng

Saturation Model Kharzeev,Levin
nucl-th/0108006 Not really designed for
frag.region...
l.25 from HERA F2 data
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Saturation model in h space...
900
546
Kharzeev, Levin nucl-th/0108006 (code from
P.Steinberg) More work needed...
200
130
53
h
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Energy Dependence Comparison to pp
Results
Its the central AA that agrees best w/ pp shape
!?

• Despite
• Hard processes
• stopping
• Rescattering
• Saturation

Systematic errors not shown
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Peripheral AA is NOT pp
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Results Limiting Fragmentation vs Centrality
Centrality dependence again.

• Each centrality exhibits limiting fragmentation
  (E-independence)
• but the shape in this region depends on
  centrality !

200 GeV
200 GeV
130 GeV
130 GeV
Fragmentation
Fragmentation
Systematic errors not shown
200 GeV Data
130 GeV Data
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Elliptic Flow A collective effect
Beams eye view of a non-central collision
Asymmetric particle distribution
f
Particles prefer to be in-plane
dN/d(f -YR ) N0 (1 2V1cos (f-YR) 2V2cos
(2(f-YR)) ... )
Elliptic flow
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Elliptic Flow
PRL 86 (2001) 402
Particle asymmetry
midrapidity h lt 1.0
V2
Hydrodynamic model
Preliminary
Normalized Multiplicity
Central
Peripheral
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Pseudorapidity dependence of V2
V2
Averaged over centrality
PHOBOS Preliminary
h
Errors are statistical only (systematic errors
0.007)
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Summary

• The source is not boost invariant
• Limiting fragmentation works over a broad
  growing region of h.
• Elliptic Flow is strongly dependent on h (y)
• AA at 200 GeV is NOT very boost-invariant!
• AA vs. pp
• Central AA pp shape very similar (?!)
• Peripheral data shows high h excess.
• Outlook
• Compare AA pp WELL at a few energies...
• QCD understanding of dN/dh in AA pp?

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For AA How about boost invariance?

Stronger different ansatz global state
between two irrelevant black walls