Transcript Document 7489535

Update on flow studies with
PHOBOS
Flow Workshop
BNL, November 2003
S. Manly
University of Rochester
Representing the
PHOBOS collaboration
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 Hołyński, 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 Wožniak, Alan Wuosmaa, Bolek Wysłouch, Jinlong Zhang
ARGONNE NATIONAL LABORATORY
INSTITUTE OF NUCLEAR PHYSICS, KRAKOW
NATIONAL CENTRAL UNIVERSITY, TAIWAN
UNIVERSITY OF MARYLAND
BROOKHAVEN NATIONAL LABORATORY
MASSACHUSETTS INSTITUTE OF TECHNOLOGY
UNIVERSITY OF ILLINOIS AT CHICAGO
UNIVERSITY OF ROCHESTER
Flow in PHOBOS
  coverage
5m
2m
1m
5
4
3
2
1
0
1
2
3
4
 coverage for vtx at z=0
5
 Data at 19.6, 130 and 200 GeV
 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
Poisson occupancy weighting
Occ ( ,  ) 

1 e

N occ
  ln( 1 
)
N unocc
Acceptance (phase space) weighting
Octagonal detector
Relative phase space weight
in annular rings = <Nocc>-1
Require circular symmetry for
equal phase space per pixel
Pixel’s azimuthal
phase space
coverage
depends on
location
 Non-flow Backgrounds
flow signal
+

Non-flow
background
z
Dilutes the flow signal
 Remove Background
 Estimate from MC and correct
Background suppression
Detector
Beampipe
Demand energy deposition be consistent with angle
dE
(keV)
Works well in Octagon
cosh 
Background!

Technique does not work in rings
because angle of incidence is ~90
Vtx holes
RingsN
Octagon

Spec holes

RingsP
Determining the collision point
High Resolution
extrapolate spectrometer tracks
Low Resolution
octagon hit density
peaks at vertex z
position
Vtx holes
RingsN
Octagon
RingsP

Spec holes

Detector symmetry
issues where SPEC
vertex efficiency
highest
Most data taken with
trigger in place to
enhance tracking
efficiency
PHOBOS flow analyses based on
subevent technique
Poskanzer and Voloshin, Phys. Rev. C58 (1998) 1671.
Azimuthal symmetry is critical
Strategies:
Hit-based analyses
 Avoid the holes – Offset vtx method
Track-based
analysis:
Avoids holes for
reaction plane
 Use the holes – Full acceptance method determination
Uses tracks passing
into spectrometer
 Use a different type of analysis, such as cumulants
Offset vtx method
Technique used
for published
130 GeV data
Octagon
RingsP

RingsN
Subevents for reaction
plane evaluation

Limited vertex range along z
 Good azimuthal symmetry
 Fewer events, no 19.6 GeV data
 Gap between subevents relatively small
Full acceptance method
Subevents for reaction plane
evaluation vary with analysis
Octagon
RingsP

RingsN

Vertex range -10<z<10
 Good statistics, 19.6 GeV data in hand
 Gap between subevents large
 Requires “hole filling”
Dealing with the holes
Inner layer of vertex detector fills
holes in top and bottom. Must map
hits from Si with different pad pattern
and radius onto a “virtual” octagon Si
layer
Octagon

RingsN

RingsP
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.)
Octagon

RingsN

RingsP
Track-based method
Subevents for reaction plane
Octagon

RingsN

 Momentum analysis
Vertex range -8<z<10
 200 GeV data
 Gap between tracks and subevents large
 Little/no background
RingsP
Track-based method – detector space
Reaction plane determined by hits in widely
separated subevent regions, symmetric in , 
Vertex measurement
Track-based method – detector space
Correlate tracks in
spectrometer to
reaction plane to
determine v2
A question to this workshop:
Are there non-flow correlations that
stretch across 3-6 units of ?
Full acceptance v1: sep=6

Full acceptance v2: sep=5.2
Offset vertex v2: sep=0.2-1.0
Track-based analysis
vz(cm)
v2 vs. centrality and energy
||<1
Preliminary v2200
Final v2130
200
130
PHOBOS Au-Au
130 GeV result: PRL 89:222301, 2002
<Npart>
v2 vs. centrality, method comparison
v2200 (hit)
v2200 (track)
hit
track
PHOBOS Preliminary
200 GeV Au-Au
<Npart>
||<1
v2 vs. pT
0<<1.5
PHOBOS preliminary
h+ + h200 GeV Au-Au
track-weighted
centrality averaging
(top 55%)
17% scale error
v2 vs.  and energy
<Npart>~190
Preliminary v2200
PHOBOS Au-Au
Final v2130
200
130
Hit-based result
v2200 & v2130 similar
130 GeV result: PRL 89:222301, 2002

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).
Directed flow: MC analysis, resolution
and background corrected, used event
plane from 1st harmonic
Input flow
Preliminary directed flow sensitivity
PHOBOS preliminary
h+ + h- Au-Au data
Flow at PHOBOS: What’s 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