QM2004

Flow in AuAu Collisions at RHIC

Marguerite Belt TonjesUniversity of Maryland

for the PHOBOS Collaboration

M.B.Tonjes, PHOBOS 2QM2004

The Collaboration

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

M.B.Tonjes, PHOBOS 3QM2004

PHOBOS Collaboration meeting, BNL Chemistry building, October 2002

M.B.Tonjes, PHOBOS 4QM2004

Detector 2000(2001)

Nearly 4π Coverage

0

+3-3 +5.4-5.4

Octagon

137000 Silicon Pad Channels

1m

Ring Counters

Spectrometer

M.B.Tonjes, PHOBOS 5QM2004

Why measure flow?

Flow is thought to be generated by compression in

the early stages of the collision

Flow probes the thermalization of the system

Elliptic and directed flow probe the evolution of

the system

M.B.Tonjes, PHOBOS 6QM2004

Flow

Flow measured by decomposing the azimuthal angle particle distributions into Fourier components:

v1 v2

directed flow elliptic flow

Reaction plane

x

z

y M. Kaneta

M.B.Tonjes, PHOBOS 7QM2004

Measuring flow in PHOBOS

Large coverage

Event-by-event

Uniform acceptance in

Separated subevents

Does not require large event sample

Measures pt dependence of v2

Use of tracks reduces background effects and reduces MC dependence

Subevents and tracks widely separated in

Hit-based method Track-based method

M.B.Tonjes, PHOBOS 8QM2004

v2(Npart) with two methods

Hit-based method

Track-based method

PHOBOS Preliminary 200 GeV AuAu

Good agreement

Nucl.Phys. A715 (2003) 611-614

h±

M.B.Tonjes, PHOBOS 9QM2004

Preliminary

PHOBOS 200 GeV0-55% central

STAR 130 GeV 4-cumulant

STAR 130 GeV 2-cumulant

STAR 130 GeV Reaction Plane5-53% central

Preliminary

PHOBOS 200 GeV0-55% central

v2 vs. pt AuAutrack-based method

v 2

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

h±

M.B.Tonjes, PHOBOS 10QM2004

v2 vs. at 130 and 200 GeV AuAu

() PRL 89, 222301 (2002)

Hit-based method

v2 has a strong dependence on

() PHOBOS Preliminary v2200

() PHOBOS v2130

Minimum Bias

h±

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

M.B.Tonjes, PHOBOS 11QM2004

width of bin

v2 vs. at 200 GeV AuAu - centrality dependence

PHOBOSPreliminary

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

Hit-based method

h±

M.B.Tonjes, PHOBOS 12QM2004

Track-basedHit-based

peripheral25-50%h±

v 2

PHOBOS Preliminary

Track-basedHit-based

midcentral15-25%h±

v 2

PHOBOS Preliminary

central3-15%h±

Track-basedHit-based

v 2

PHOBOS Preliminary

v2 vs. at 200 GeV AuAu - comparison of methods

M.B.Tonjes, PHOBOS 13QM2004

PHOBOS Preliminary

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

Preliminary

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

8x10-2

2x10-2

4x10-2

6x10-2

Hit-based & track-based data combined

The peripheral

data at

midrapidity is

not flat within

90% confidence

level

h±

v 2

Different centralities appear to differ only by a scale factor (within errors)

M.B.Tonjes, PHOBOS 14QM2004

v1 measurement: hit-based method

z

Ring RingOctagon

v1

Reaction plane for Octagon calculated from symmetric subevents in the Rings (and vice-versa)

M.B.Tonjes, PHOBOS 15QM2004

v1 measured at different energiesv 1

v 1

y

STAR AuAu √sNN = 200 GeV

Minimum Bias

10-70% central

nucl-ex/0310029

Phys.Rev.C68, 034903, 2003

(reflected)

±

h±

NA49 PbPb 158 GeV√sNN = 17.2 GeV

M.B.Tonjes, PHOBOS 16QM2004

v1 at 19.6 GeV AuAuv 1

PHOBOS Preliminary

PHOBOS 6-55% centralh±

M.B.Tonjes, PHOBOS 17QM2004

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±

±

v1: 19.6 GeV AuAu & 17.2 GeV PbPb

M.B.Tonjes, PHOBOS 18QM2004

v1 at 130 GeV AuAuv 1

PHOBOS Preliminary

PHOBOS 6-55% central

(different scale)

h±

M.B.Tonjes, PHOBOS 19QM2004

v1 at 200 GeV AuAuv 1

PHOBOS Preliminary

PHOBOS 6-55% central h±

M.B.Tonjes, PHOBOS 20QM2004

STAR AuAu 200 GeV 10-70% central

v1 at 200 GeV AuAu:PHOBOS & STARv 1

nucl-ex/0310029

PHOBOS Preliminary

PHOBOS 6-55% centralh±

M.B.Tonjes, PHOBOS 21QM2004

PHOBOS Preliminary

v 1

h±

6-55%central

19.6 GeV130 GeV200 GeV

v1 at different energies in AuAu

PHOBOS Preliminaryh± 6-55% central

200 GeV

PHOBOS Preliminary

19.6 GeV h± 6-55% central

v1 v1

M.B.Tonjes, PHOBOS 22QM2004

19.6 GeV130 GeV200 GeV

v 1

’=-ybeam

PHOBOS Preliminary

v1 19.6, 130, 200 GeV AuAu (’)

v1 from positive used only

h±

PHOBOS Au+Au

dN

ch/d

’/<

Np

art>

/2

6% central

PRL 91, 052303 (2003)

’

M.B.Tonjes, PHOBOS 23QM2004

Conclusions

v2 vs pt demonstrates that we do not measure significant non-flow effects

v2 has been measured as a function of and centrality over a large range in pseudorapidity

v1 has been measured over a range of energies from 19.6 to 200 GeV over a large region of in PHOBOS

v1 clearly changes behavior from low (19.6 GeV) to high (200 GeV) energy

v1 in the mid-’ region is reminiscent of limiting fragmentation

M.B.Tonjes, PHOBOS 24QM2004