Transcript Document 7489437
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 Ho łyński, 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 Wo žniak, 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
1m 2m 5m 5 4 3 2 1 0 1 2 3 coverage for vtx at z=0 4 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
ln( 1
N occ N unocc
)
Acceptance (phase space) weighting Octagonal detector Relative phase space weight in annular rings =
Non-flow Backgrounds
z flow signal + Non-flow background Dilutes the flow signal
Remove Background
Estimate from MC and correct
Background suppression Detector Beampipe
dE
(keV)
Demand energy deposition be consistent with angle cosh
Background!
Works well in Octagon Technique does not work in rings because angle of incidence is ~90
Spec holes
RingsN Octagon
Vtx holes
RingsP
Determining the collision point
High Resolution Low Resolution extrapolate spectrometer tracks octagon hit density peaks at vertex z position
Spec holes
RingsN Octagon
Vtx holes
RingsP
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 Track-based analysis:
Avoid the holes – Offset vtx method
Use the holes – Full acceptance method Avoids holes for reaction plane determination Uses tracks passing into spectrometer
Use a different type of analysis, such as cumulants
Offset vtx method
RingsN
Subevents for reaction plane evaluation
Octagon RingsP
Limited vertex range along z
Good azimuthal symmetry
Fewer events, no 19.6 GeV data
Gap between subevents relatively small
Full acceptance method
RingsN
Subevents for reaction plane evaluation vary with analysis
Octagon RingsP
Vertex range -10
Good statistics, 19.6 GeV data in hand
Gap between subevents large
Requires “hole filling”
Dealing with the holes
RingsN
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 RingsP
Dealing with the holes
RingsN
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 RingsP
Track-based method
RingsN
Subevents for reaction plane
Octagon RingsP
Vertex range -8
Momentum analysis
200 GeV data
Gap between subevents large
Gap between tracks and subevents large
Track-based method
Momentum analysis
200 GeV data v z (cm)
Gap between subevents large
Gap between tracks and subevents large
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 v 2
A question to this workshop: Are there non-flow correlations that stretch across 3-6 units of
?
Full acceptance v 1 :
sep =6 Full acceptance v 2 :
sep =5.2
Offset vertex v 2 :
sep =0.2-1.0
Track-based analysis v z (c m)
v
2
vs. centrality and energy
|
|<1 Preliminary v 2 200 Final v 2 130 200 130
130 GeV result: PRL 89:222301, 2002 PHOBOS Au-Au
v
2
vs.
centrality
, method comparison
v 2 200 (hit) v 2 200 (track) |
|<1 track hit
PHOBOS Preliminary 200 GeV Au-Au
PHOBOS preliminary
h + + h -
200 GeV Au-Au
v
2
vs. p
T 0<
<1.5
track-weighted centrality averaging (top 55%) 17% scale error
v
2
vs.
and energy
PHOBOS Au-Au
Can we use what is now known about the forward region to qualitatively 130 v2(eta)?
Preliminary
v 2 200 Final v 2 130 Hit-based result v 2 200 & v 2 130 similar
130 GeV result: PRL 89:222301, 2002
dN/dP T BRAHMS Collaboration, Phys. Rev. Lett 91 (2003) 072305
V 2 vs p T
0, three centrality bins STAR Collaboration, Phys.Rev.Lett. 90 (2003) 032301 Preliminary STAR data at
3.3, one centrality bin
Need data at
2.2 not 3.3
At
0, V 2 (p T )=0.1p
T . At
3.3, V 2 (p T )=0.08p
T . Assume v 2 (p T )=0.085p
T at
2.2.
Parametrize slope as function of centrality at low p T and scale values at
2.2 by (0.085/0.1)value at
0 Then choose coefficients corresponding to PHOBOS centrality bins and convolute with dN/dp T with a 200 MeV momentum cutoff.
Finally, integrate.
PHOBOS result overlayed with plausible expectation given Brahms dN/dp T and STAR FTPC v 2 (p T )
(Plausible expectation)
Plausible that change in slope of v 2 (p T ) leads to drop in v 2 (
)
Directed flow: MC analysis, resolution and background corrected, used event plane from 1 st 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 mid-z technique
Goal is to release preliminary v 1 (
) at 19.6, 130 and 200 GeV for Quark Matter