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. The Phobos Collaboration. Birger Back, Mark Baker, Maarten Ballintijn, Donald Barton, Bruce Becker, Russell Betts,

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Update on flow studies with PHOBOS

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Update on flow studies with phobos

Update on flow studies with PHOBOS

Flow Workshop

BNL, November 2003

S. Manly

University of Rochester

Representing the PHOBOS collaboration


Update on flow studies with phobos

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 LABORATORYBROOKHAVEN NATIONAL LABORATORY

INSTITUTE OF NUCLEAR PHYSICS, KRAKOWMASSACHUSETTS INSTITUTE OF TECHNOLOGY

NATIONAL CENTRAL UNIVERSITY, TAIWANUNIVERSITY OF ILLINOIS AT CHICAGO

UNIVERSITY OF MARYLANDUNIVERSITY OF ROCHESTER


Update on flow studies with phobos

Flow in PHOBOS


Update on flow studies with phobos

5m

2m

5

4

3

2

1

0

1

2

3

4

5

1m

h

coverage for vtx at z=0

  •  coverage

  • Data at 19.6, 130 and 200 GeV


Update on flow studies with phobos

  • 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


Update on flow studies with phobos

Poisson occupancy weighting


Update on flow studies with phobos

Octagonal detector

Require circular symmetry for equal phase space per pixel

Pixel’sazimuthalphase space coverage depends on location

Acceptance (phase space) weighting

Relative phase space weight in annular rings = <Nocc>-1


Update on flow studies with phobos

f

z

+

Non-flow background

  • Non-flow Backgrounds

flow signal

Dilutes the flow signal

  • Remove Background

  • Estimate from MC and correct


Update on flow studies with phobos

Detector

Beampipe

dE

(keV)

cosh h

Background!

h

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


Update on flow studies with phobos

Vtx holes

RingsN OctagonRingsP

Spec holes

f

h


Update on flow studies with phobos

High Resolution

Low Resolution

Determining the collision point

octagon hit density peaks at vertex z position

extrapolate spectrometer tracks


Update on flow studies with phobos

Vtx holes

Spec holes

RingsN OctagonRingsP

f

h

Detector symmetry issues where SPEC vertex efficiency highest

Most data taken with trigger in place to enhance tracking efficiency


Update on flow studies with phobos

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


Update on flow studies with phobos

RingsN Octagon RingsP

f

h

Limited vertex range along z

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


Update on flow studies with phobos

RingsN OctagonRingsP

Vertex range -10<z<10

f

h

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”


Update on flow studies with phobos

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

RingsN Octagon RingsP

f

h

Dealing with the holes


Update on flow studies with phobos

RingsN Octagon RingsP

f

h

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.)


Update on flow studies with phobos

RingsN OctagonRingsP

Vertex range -8<z<10

f

h

Track-based method

Subevents for reaction plane

  • Momentum analysis

  • 200 GeV data

  • Gap between tracks and subevents large

  • Little/no background


Update on flow studies with phobos

Reaction plane determined by hits in widely separated subevent regions, symmetric in , 

Vertex measurement

Track-based method – detector space


Update on flow studies with phobos

Correlate tracks in spectrometer to reaction plane to determine v2

Track-based method – detector space


Update on flow studies with phobos

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

h

vz(cm)


Update on flow studies with phobos

Preliminary v2200

Final v2130

v2 vs. centrality and energy

|h|<1

v2

200

130

PHOBOS Au-Au

<Npart>

130 GeV result: PRL 89:222301, 2002


Update on flow studies with phobos

v2 vs.centrality, method comparison

v2

|h|<1

v2200 (hit)

v2200 (track)

track

hit

PHOBOS Preliminary

200 GeV Au-Au

<Npart>


Update on flow studies with phobos

v2 vs.pT

0<h<1.5

v2

PHOBOS preliminary

h+ + h-

200 GeV Au-Au

track-weighted centrality averaging

(top 55%)

17% scale error


Update on flow studies with phobos

v2 vs. and energy

<Npart>~190

v2

Preliminaryv2200

PHOBOS Au-Au

Final v2130

200

130

Hit-based result

v2200 & v2130 similar

h

130 GeV result: PRL 89:222301, 2002


Update on flow studies with phobos

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).


Update on flow studies with phobos

Input flow

Directed flow: MC analysis, resolution and background corrected, used event plane from 1st harmonic

A little Quark Matter preview


Update on flow studies with phobos

Preliminary directed flow sensitivity

PHOBOS preliminary

h+ + h-Au-Au data

A little Quark Matter preview


Update on flow studies with phobos

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


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