Charged Particle FLOW measurement for ||<5.3 with

the PHOBOS detector

Inkyu Park (Univ. of Rochester)for the PHOBOS Collaboration

2000-01-17 Flow@PHOBOS - Inkyu Park 2

ARGONNE NATIONAL LABORATORY Birger Back, Nigel George, Alan Wuosmaa

BROOKHAVEN NATIONAL LABORATORYMark Baker, Donald Barton, Alan Carroll, Stephen Gushue, George Heintzelman, Robert Pak,

Louis Remsberg, Peter Steinberg, Andrei SukhanovINSTITUTE OF NUCLEAR PHYSICS, KRAKOW

Andrzej Budzanowski, Roman Holynski, Jerzy Michalowski, Andrzej Olszewski, Pawel Sawicki, Marek Stodulski, Adam Trzupek, Barbara Wosiek, Krzysztof Wozniak

MASSACHUSETTS INSTITUTE OF TECHNOLOGYWit Busza*, Patrick Decowski, Kristjan Gulbrandsen, Conor Henderson, Jay Kane, Judith Katzy,

Piotr Kulinich, Johannes Muelmenstaedt, Heinz Pernegger, Corey Reed, Christof Roland, Gunther Roland,

Leslie Rosenberg, Pradeep Sarin, Stephen Steadman, George Stephans, Gerrit van Nieuwenhuizen,

Carla Vale, Robin Verdier, Bernard Wadsworth, Bolek WyslouchNATIONAL CENTRAL UNIVERSITY, TAIWAN

Willis Lin, Jawluen TangUNIVERSITY OF ROCHESTER

Joshua Hamblen, Erik Johnson, Nazim Khan, Steven Manly, Inkyu Park, Wojtek Skulski, Ray Teng, Frank Wolfs

UNIVERSITY OF ILLINOIS AT CHICAGORussell Betts, Clive Halliwell, David Hofman, Burt Holzman, Wojtek Kucewicz, Don McLeod,

Rachid Nouicer, Michael ReuterUNIVERSITY OF MARYLAND

Richard Bindel, Edmundo Garcia-Solis, Alice Mignerey

*spokesperson

PHOBOS Collaboration

2000-01-17 Flow@PHOBOS - Inkyu Park 3

Physics Goal of RHIC & Flow

Flow

affect other physics: HBT, Spectra, etc

dN/d(R ) = N0 (1 + 2V1cos (R) + 2V2cos (2(R) + ... )

In-plane OR Out-of-plane

Elliptic flow Directed flow

Flow strength

Equation of state

Initial state anisotropy

b (reaction plane)

Degree of thermalization

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PHOBOS Detector setup 2000

Ring Counters

Paddle Trigger Counter

Spectrometer

TOF

Octagon+Vertex

See Robert Pak’s talk

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Au Aux

z

PPPN

ZDC P

ZDC N

Negative

Paddles

Positive Paddles

Paddle counters : Trigger & Centrality

Paddle Signal

Np

art

Paddle Signal

Data MC

See Judith Katzy’s talk

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Spectrometer : Vertex Reconstruction

form 3D vertex z

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octagon

Ring counter

-1.1m

1.1m2.3m

-2.3m

5.0m

-5.0m

• || < 5.3 (, 0 (

Interaction Point

Octagon and Ring detectors

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Hit Definition

Particle direction

Charged particle

deposit energy in pad

hit

event vertex 1 hit = pad with energy > 60

keV

Octagon Ring

Energy deposit (keV) Energy deposit (keV)

60keV 60keV

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Event Selectionvertex available Rings PRings N

• To cover pseudo-rapidity -2.0 to 2.0, only events with vertex -38cm to -30 cm are used

• Rings will cover 3.0 < || < 5.3

• 13K events are used finally for the analysis

-56cm -14cmOctagon

z

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Centrality Bins

Acceptance affected by various strict vertex cuts

Normalized Paddle Signal

Triggered

Accepted

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Event Plane Reconstruction

n = tan-1 ( Xn / Yn ) / n

(Xn,Yn)=w cos(n), w sin(n) )

n

Xn

Yn

(p

ixel

num

ber)

Z (pixel number)

w is weight to compensate for detector

related azimuthal asymmetries

(inverse of hit density)

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Particle distribution w.r.t. Event Plane

N V 2

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• If we know the reaction plane perfectly: Vn = < cos (n(R)) >

Flow Analysis* (Subevent correlation)

• In real experiment, R is unknown: use n

Vnobs = < cos (n(n)) >

<cos(nna,bRcos(n(n

a nb))> )1/2

• Finally, correct for event plane resolution

Vn= Vnobs / < cos (n(n R)) >

-2.0 < < -0.1

RingPRingNSubE (a) SubE (b)

na n

b

* Phys. Rev. C 58, 1671

A. M. Poskanzer,

S. A. Voloshin

0.1 < < 2.0

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Subevent Plane Correlation

Normalized Paddle Signal

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With our hit counting method, high occupancy reduces flow

signal

Occupancy Correction

V2corr = V2

raw / (1 -Occ)

V2raw = < cos (2(hit2)) >

Centrality bin

V2 = V2corr / cos (2(

a b)) > )1/2

Occupancy = fraction of hit

pads

Independent of the magnitude of flow

MC

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Centrality Dependence

midrapidity : || < 1.0

Centrality bin

V2PHOBOS Preliminary

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Centrality Dependence

Hydrodynamic model

V2

Normalized Paddle Signal Errors are statistical only

(systematic errors ~ 0.007)

midrapidity : || < 1.0

SPS

AGS

(STAR : Normalized Nch )

Preliminary

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Pseudorapidity dependence of V2

V2 Averaged over centrality

PHOBOS Preliminary

Errors are statistical only (systematic errors ~ 0.007)

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Pseudorapidity dependence of V2

V2 PHOBOS Preliminary STAR (PRL)

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0 1 2 3 4 5 6

SPS NA49 (QM99)

rapidity

PHOBOS Errors are statistical only (systematic errors ~ 0.007)

STAR : averaged over their centrality

Pion (b<11fm)

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• Elliptic Flow at midrapidity reaches 6-7% in

peripheral collisions, and drops in central

collisions

• Elliptic Flow is a strong function of

pseudorapidity

• Indication of sensitivity to V1 (we are

studying…)

Thank you!

Summary