3 Remarks on Fluctuations in Hadron Production at RHIC

Gunther Roland - MITPHOBOS ISMD’05

3 Remarks on Fluctuations in

Hadron Production at RHIC

Gunther Roland Massachusetts Institute of Technology

New Results from the PHOBOS Collaboration

Gunther Roland - MITPHOBOS ISMD’05 2

Burak Alver, Birger Back, Mark Baker, Maarten Ballintijn, Donald Barton, Russell Betts, Richard

Bindel,

Wit Busza (Spokesperson), Zhengwei Chai, Vasundhara Chetluru, Edmundo García, Tomasz

Gburek, Kristjan Gulbrandsen, Clive Halliwell, Joshua Hamblen, Ian Harnarine, Conor Henderson,

David Hofman, Richard Hollis, Roman Hołyński, Burt Holzman, Aneta Iordanova, Jay Kane,Piotr

Kulinich, Chia Ming Kuo,

Wei Li, Willis Lin, Constantin Loizides, Steven Manly, Alice Mignerey, Gerrit van Nieuwenhuizen,

Rachid Nouicer, Andrzej Olszewski, Robert Pak, Corey Reed, Eric Richardson, Christof Roland,

Gunther Roland, Joe Sagerer, Iouri Sedykh, Chadd Smith, Maciej Stankiewicz, Peter Steinberg,

George Stephans, Andrei Sukhanov, Artur Szostak, Marguerite Belt Tonjes, Adam Trzupek,

Sergei Vaurynovich, Robin Verdier, Gábor Veres, Peter Walters, Edward Wenger, Donald

Willhelm,

Frank Wolfs, Barbara Wosiek, Krzysztof Woźniak, Shaun Wyngaardt, Bolek Wysłouch

ARGONNE NATIONAL LABORATORY BROOKHAVEN NATIONAL LABORATORYINSTITUTE OF NUCLEAR PHYSICS PAN, KRAKOW MASSACHUSETTS INSTITUTE OF TECHNOLOGY

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

PHOBOS Collaboration


RHIC

Heavy Ion Collision


PHOBOS Experiment


centrality

Au+Au : PRL 91, 052303 (2003)d+Au : PRL 93, 082301 (2004)

19.6 GeV 62.4 GeV 130 GeV 200 GeVpreliminary

preliminary preliminary

Cu+Cu

d+Au

Au+Au

PHOBOS

Charged Hadron dN/d


1st Remark

To good approximation ( 10-4), all events are “the same”


Raw dN/d seen by PHOBOS

Search for unusual events:I. Multiplicity Fluctuations Integral II. Shape Fluctuation 2 of single-event vs average


Unusual Events in Au+Au

Multiplicity distribution and 2 (shape) distribution shows distinct tails - O(10-4)

200 Events

Total Multiplicity Fluctuations Shape Fluctuations

2M Events

Fre

qu

enc

y o

f ev

ents


Possible Explanation

Rate of unusual events correlates with ‘luminosity’ - Consistent with collision-pileup as source of rare events

Shape FluctuationsTotal Multiplicity Fluctuations


2nd Remark

Hadrons are not produced one-by-one, but in “clusters”


Analysis Concept

RMS used to determine σC

P-N

P

NP+N

(Impact parameter)

(Partitioning)

PN

Forward/backward multiplicity fluctuations


Clusters and σ2C

PN

Forward/backward correlations give access to cluster structure of particle production


Cluster-size from F/B fluctuations

40-60% peripheral 0-20% central

PHOBOS 200 GeVAu+Au preliminary

PHOBOS 200 GeVAu+Au preliminary

Forward/backward correlations suggest effective cluster size of 2-2.5 for 200 GeV Au+Au


Clusters in p+p

546 GeV

P+N

UA5: Phys.Lett.B123:361,1983

Keff

Reminiscent of results from p+p


3rd Remark

Initial state shape fluctuations drive expansion dynamics


“Elliptic Flow”

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

Non-central collision:

Initial state eccentricity


“Elliptic Flow”

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

TimeTransverse Plane

Azimuthal Angle (rad)

Non-central collision:

Initial state eccentricity

Elliptic Flow:

Final state anisoptropy

2*v2


preliminary

PHOBOS 200 GeV h±

Statistical errors only

Cu+Cupreliminary

Au+Au

PHOBOS 200 GeV Statistical errors only

v2 for Au+Au follows initial state eccentricity

v2 near mid-rapidity

Elliptic Flow vs Npart


preliminary

PHOBOS 200 GeV h±

Statistical errors only

Cu+Cupreliminary

Au+Au

PHOBOS 200 GeV Statistical errors only

Substantial v2 even for most central bin in Cu+Cu

v2 near mid-rapidity

Elliptic Flow vs Npart


Standard Eccentricity

x

y Nucleus 2Nucleus 1

ParticipantRegion

b

Au+AuCu+Cu

Au+Au

Eccentricity Calculation



x


ParticipantRegion

b

Au+AuCu+Cu

Au+Au

Nucleus 1

Nucleus 2

Participant Region

x

y

Participant Eccentricity

b

Au+AuCu+Cu

Au+Au

Eccentricity Calculation



Cu+Cu

Au+Au

Low Density Limit:STAR, PRC 66 034904 (2002)Voloshin, Poskanzer, PLB 474 27 (2000)Heiselberg, Levy, PRC 59 2716, (1999)

Density Scaling



Cu+Cu

Au+Au

Participant Eccentricity

Cu+Cu

Au+Au

Low Density Limit:STAR, PRC 66 034904 (2002)Voloshin, Poskanzer, PLB 474 27 (2000)Heiselberg, Levy, PRC 59 2716, (1999)

Density Scaling

“Participant Eccentricity” allows v2 scaling from

Cu+Cu to Au+Au


Summary

Initial state shape fluctuations drive expansion dynamics

To good approximation ( 10-4), all events are “the same”

Hadrons are not produced one-by-one, but in “clusters”


Backup

Raw data


Backup


Cu+Cupreliminary

Au+Au

PHOBOS 200 GeV

“Participant Eccentricity” allows v2 scaling from

Cu+Cu to Au+Au

Participant Eccentricity PHOBOS 200 GeV

Au+AuCu+Cupreliminary


L~A1/3

Ncoll= # of NN collisions: ~A4/3

Npart/2 ~ A

“Participants”

“Collisions”

PHOBOS Glauber MC

Au+Au

Cu+Cu

Au+Au

Cu+Cu

Backup


Backup

PHOBOS Glauber MC

• Au+Au vs Cu+Cu– Interplay of initial geometry and initial density– Test ideas of early thermalization and collectivity

wrt reaction plane

22

22

xy

xy

σσσσ

ε+

−=

x


ParticipantRegion

Au+Au

Cu+Cu


Backup

Eccentricity difference is important for same centrality selection.

V2(pT) for Cu-Cu is similar v2(pT) for Au-Au when scaled by εpart

PHOBOS preliminary h±

0-50% centralityPHOBOS preliminary h±

0-50% centrality

PHOBOS preliminary h±

0-50% centrality


Au+Au: PRL 94, 082304 (2005), PLB 578, 297 (2004)

Cu+Cupreliminary

Au+Au

Backup

3 Remarks on Fluctuations in Hadron Production at RHIC

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