Update on flow studies with PHOBOS

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Update on flow studies with PHOBOS
Flow Workshop BNL, November 2003
S. Manly University of Rochester Representing the
PHOBOS collaboration
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The Phobos Collaboration
Birger Back, Mark Baker, Maarten Ballintijn,
Donald Barton, Bruce Becker, Russell Betts,
Abigail Bickley, Richard Bindel, Andrzej
Budzanowski, Wit Busza (Spokesperson), Alan
Carroll, Zhengwei Chai, 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, 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, Iouri Sedykh, Wojtek Skulski, Chadd
Smith, 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 Woniak, Alan Wuosmaa, Bolek
Wyslouch, Jinlong Zhang 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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Flow in PHOBOS
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• ? coverage

• Data at 19.6, 130 and 200 GeV

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• Pixelized detector

Hit saturation, grows with occupancy Sensitivity
to flow reduced
Can correct using analogue energy deposition
or- measure of occupied and unoccupied pads in
local region assuming Poisson statistics
Poisson occupancy correction
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Poisson occupancy weighting
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Acceptance (phase space) weighting
Relative phase space weight in annular rings
ltNoccgt-1
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• Non-flow Backgrounds

flow signal
Dilutes the flow signal

• Remove Background
• Estimate from MC and correct

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Background suppression
Demand energy deposition be consistent with angle
Works well in Octagon
Technique does not work in rings because angle of
incidence is 90?
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Determining the collision point
octagon hit density peaks at vertex z position
extrapolate spectrometer tracks
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Detector symmetry issues where SPEC vertex
efficiency highest
Most data taken with trigger in place to enhance
tracking efficiency
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PHOBOS flow analyses based on subevent
technique Poskanzer and Voloshin, Phys. Rev. C58
(1998) 1671. Azimuthal symmetry is critical
Strategies
Hit-based analyses
Track-based analysis Avoids holes for reaction
plane determination Uses tracks passing into
spectrometer

• Avoid the holes Offset vtx method

• Use the holes Full acceptance method

• Use a different type of analysis, such as
  cumulants

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Offset vtx method
Subevents for reaction plane evaluation
Technique used for published 130 GeV data

• Good azimuthal symmetry
• Fewer events, no 19.6 GeV data
• Gap between subevents relatively small

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Full acceptance method
Subevents for reaction plane evaluation vary with
analysis

• Good statistics, 19.6 GeV data in hand
• Gap between subevents large
• Requires hole filling

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Dealing with the holes
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Dealing with the holes
Fill spectrometer holes by extrapolating hit
density from adjoining detectors onto a virtual
Si layer. (Actual spec layer 1 is much smaller
than the hole in the octagon.)
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Track-based method
Subevents for reaction plane

• Momentum analysis
• 200 GeV data
• Gap between tracks and subevents large
• Little/no background

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Track-based method detector space
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Track-based method detector space
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A question to this workshop Are there non-flow
correlations that stretch across 3-6 units of ??
Full acceptance v1 ?sep6 Full acceptance v2
?sep5.2 Offset vertex v2 ?sep0.2-1.0 Track-base
d analysis
h
vz(cm)
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v2 vs. centrality and energy
hlt1
v2
200
130
PHOBOS Au-Au
ltNpartgt
130 GeV result PRL 89222301, 2002
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v2 vs. centrality, method comparison
v2
hlt1
v2200 (hit)
v2200 (track)
track
hit
PHOBOS Preliminary 200 GeV Au-Au
ltNpartgt
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v2 vs. ?pT
0lthlt1.5
v2
PHOBOS preliminary h h- 200 GeV Au-Au
track-weighted centrality averaging
(top 55)
17 scale error
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130 GeV result PRL 89222301, 2002
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A. Poskanser showed in his talk that STAR agrees
with the PHOBOS v2(?). It will be interesting to
see if it is possible to deconvolute the STAR and
BRAHMS results in the forward region to determine
what fraction of the drop in v2(?) comes from
dN/dpT and what fraction comes from v2(pT).
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Directed flow MC analysis, resolution and
background corrected, used event plane from 1st
harmonic
A little Quark Matter preview
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Preliminary directed flow sensitivity
PHOBOS preliminary h h- Au-Au data
A little Quark Matter preview
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Flow at PHOBOS Whats new?

• 200 GeV analyses
• Finalizing systematics
• Plan to release soon final results in 3 bins of
  centrality

• Directed flow (v1)
• Still optimizing analysis and working to
  understand fine points of data analysis using
  full acceptance technique
• Goal is to release preliminary v1(?) at 19.6,
  130 and 200 GeV for Quark Matter