winter workshop in nuclear physics trelawny beach, jamaica march , 2003 steven.manly@rochester

March, 2004Winter Workshop - Jamaica - S. Manly 1

Winter Workshop in Nuclear Physics

Trelawny Beach, JamaicaMarch , 2003

[email protected]://hertz.pas.rochester.edu/smanly/

The view from my office webcam: while I’m here working, my group is enjoying spring break in Rochester

Why yes, this is a frisbee!

Collective flow with PHOBOSSteven Manly

University of Rochesterrepresenting

PHOBOS


Collaboration meeting, BNL October 2002

Birger Back, Mark Baker, Maarten Ballintijn, Donald Barton, Russell Betts, Abigail Bickley,

Richard Bindel, 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 BROOKHAVEN NATIONAL LABORATORYINSTITUTE OF NUCLEAR PHYSICS, KRAKOW MASSACHUSETTS INSTITUTE OF TECHNOLOGY

NATIONAL CENTRAL UNIVERSITY, TAIWAN UNIVERSITY OF ILLINOIS AT CHICAGOUNIVERSITY OF MARYLAND UNIVERSITY OF ROCHESTER


Flow in PHOBOSFlow in PHOBOS


coverage

Data at 19.6, 130 and 200 GeV

1m2m

5m

0 1 2 3 4 512345

coverage for vtx at z=0


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 Poisson occupancy correctioncorrection


Acceptance (phase space) weighting

Octagonal detector

Require circular symmetry for equal phase space per pixel

Pixel’s azimuthal phase space coverage depends on location

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


z

Dilutes the flow signal

Remove Background

Estimate from MC and correct

flow signal

Non-flow background

+

Non-flow Backgrounds


Background suppression

Works well in Octagon

dE

(keV)

cosh

Background!

Technique does not work in rings because angle of incidence is ~90

Beampipe

Detector

Demand energy deposition be consistent with angle


RingsN Octagon RingsP

Spec holes

Vtx holes


Determining the collision point

High Resolution

extrapolate spectrometer tracks

Low Resolution

octagon hit density peaks at vertex z

position



Spec holes

Vtx holes

Detector symmetry issues where SPEC vertex efficiency highest

Most data taken with trigger in place to enhance tracking efficiency



Offset vtx method

Limited vertex range along z

Subevents for reaction plane evaluation

Good azimuthal symmetry

Fewer events, no 19.6 GeV data

Gap between subevents relatively small

Technique used for published elliptic flow signal at 130 GeV



Full acceptance method

Vertex range -10<z<10

Subevents for reaction plane evaluation vary with analysis

Good statistics, 19.6 GeV data available

Gap between subevents large

Requires “hole filling”

Technique used for elliptic and directed flow signal at all energies (only directed flow released to date, elliptic flow coming soon)


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


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.)



Track-based method

Vertex range -8<z<10

Subevents for reaction plane

Momentum analysis

200 GeV data

Gap between tracks and subevents large

Little/no background


Directed flow

Charged hadrons

6-55% central AuAu


v 1

PHOBOS Preliminary

PHOBOS AuAu √sNN=19.6 GeV

NA49 PbPb √sNN=17.2 GeV

Phys.Rev.C68, 034903, 2003

6-55%

MinimumBias

h±

±

19.6 GeV AuAu & 17.2 GeV PbPb


STAR AuAu 200 GeV 10-70% central

v1 at 200 GeV AuAu:PHOBOS & STARv 1

STAR, PRL 92 (2004) 062301

PHOBOS Preliminary

PHOBOS 6-55% centralh±


In target frame of reference, directed flow exhibits signal consistent

with limiting fragmentation


() PHOBOS Preliminary v2200

() PHOBOS v2130

Minimum Bias

h±

v2 vs. at 130 and 200 GeV AuAu

() PRL 89, 222301 (2002)

Hit-based method

() Nucl.Phys. A715 (2003) 611-614


width of bin

v2 vs. 200 GeV centrality dependence

PHOBOSPreliminary

central 3-15%midcentral 15-25%peripheral 25-50%

Hit-based method

h±


Track-basedHit-based

peripheral25-50%h±

v 2

PHOBOS Preliminary


midcentral15-25%h±

v 2

PHOBOS Preliminary

central3-15%h±


v 2

PHOBOS Preliminary

v2 vs. 200 GeV method comparison


Combined hit (offset vertex) and track based

results for v2 vs. || at 200 GeV (Au-Au)


Preliminary

PHOBOS 200 GeV0-55% central

track-based methodv 2

pt (GeV/c)• Nucl.Phys. A715 (2003) 611-614

h± STAR 130 GeV 4-cumulant

STAR 130 GeV 2-cumulant

STAR 130 GeV Reaction Plane5-53% central

Preliminary


pt (GeV/c)

v 2v2 vs. pt AuAu




STAR 130 GeV Reaction Plane5-53% central

Preliminary


pt (GeV/c)

v 2PHOBOS signal not pt weighted, thus dominated by low pt

hits where STAR 2- and 4-particle cumulants have small absolute difference


y vs.

Get a suppression in the spectra which is largest at low pt and small ||. It vanishes at large || and high pt.

Gives the famous dip in multiplicity distribution.

If integrating v2 over pt, get suppression of the lower pt part (where v2 is small) and the signal should rise.


Transformation of spectra from to y leads to

suppression of multiplicity at low pt and low ||

This leads to an enhancement of inclusive v2

at mid-

P. Kolb, Proc. of 17th Winter Workshop on Nuclear Dynamics (2001)

T. Hirano, BNL-Riken Workshop on Collective Flow and the QGP (Nov. 2003)

~10%


Limiting fragmentation of elliptic flow

PHOBOS Preliminary v2200

PHOBOS v2130


Scaled by “Kolb factor”

Limiting fragmentation of elliptic flow

PHOBOS Preliminary v2200

PHOBOS v2130


Conclusions Directed flow measured at 19.6, 130 and 200 GeV

Mild disagreement with STAR about || where v1 kicks in, but both see flat slope at mid-

v1 shows a limiting fragmentation behavior similar to the multiplicity

v2() hit and track results agree. Likely there is very little non-flow correlations. Expect only small difference between v2() and v2(y).

Hint of limiting fragmentation behavior in v2. Expect better results on this soon

winter workshop in nuclear physics trelawny beach, jamaica march , 2003 steven.manly@rochester

Documents

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