Charged Particle Multiplicities from Cu+Cu, Au+Au and d+Au Collisions at RHIC

Charged Particle Charged Particle Multiplicities from Multiplicities from

Cu+Cu, Au+Au and Cu+Cu, Au+Au and d+Au Collisions at RHICd+Au Collisions at RHIC

Aneta IordanovaAneta Iordanova

University of Illinois at ChicagoUniversity of Illinois at Chicago

for the collaborationfor the collaboration

22DNP, Nashville, 28 Oct 200DNP, Nashville, 28 Oct 20066

Aneta Iordanova Aneta Iordanova

Phobos CollaborationPhobos Collaboration

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

Bindel,

Wit Busza (Spokesperson), Vasundhara Chetluru, Edmundo García, Tomasz Gburek, Joshua

Hamblen, Conor Henderson, David Hofman, Richard Hollis, Roman Hołyński, Burt Holzman, Aneta

Iordanova, Chia Ming Kuo, Wei Li, Willis Lin, Constantin Loizides, Steven Manly, Alice Mignerey,

Gerrit van Nieuwenhuizen, Rachid Nouicer, Andrzej Olszewski, Robert Pak, Corey Reed, Christof

Roland, Gunther Roland, Joe Sagerer, Peter Steinberg, George Stephans, Andrei Sukhanov,

Marguerite Belt Tonjes, Adam Trzupek, Sergei Vaurynovich, Robin Verdier, Gábor Veres, Peter

Walters, Edward Wenger, Frank Wolfs, Barbara Wosiek, Krzysztof Woźniak, 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 detector



OutlineOutline

Control parameters of a heavy ion collisionControl parameters of a heavy ion collision EnergyEnergy

19.6 - 200 GeV19.6 - 200 GeV Colliding system sizeColliding system size

centrality Ncentrality Npartpart from 3.5 (d+Au) – 360 (Au+Au) from 3.5 (d+Au) – 360 (Au+Au) SpeciesSpecies

p+p, d+Au, Cu+Cu and Au+Aup+p, d+Au, Cu+Cu and Au+Au

Global features of charged particle production Global features of charged particle production (observables)(observables) dNdNchch/d/d shapes (particle distributions in shapes (particle distributions in )) Mid-rapidity factorizationMid-rapidity factorization

DataData

comparison of Au+Au and Cu+Cucomparison of Au+Au and Cu+Cu

d+Au and p+pd+Au and p+p



d+Au

Charged hadron dNCharged hadron dNchch/d/d distribution distribution

centrality

Au+Au : PRL 91, 052303 (2003) Au+Au : PRC 74, 021901 (2006) d+Au : PRC 72, 031901 (2005)

19.6 GeV 62.4 GeV 130 GeV 200 GeV

dN/d distribution

preliminary preliminary

Au

+A

u d

ata

Cu

+C

u d

ata

With energy:With energy: Height increasesHeight increases Width increases (in Width increases (in space) space)

With centrality(0-50% central):With centrality(0-50% central): Height increasesHeight increases

With species:With species: Same systematic trendsSame systematic trends



Comparison of Au+Au and Cu+CuComparison of Au+Au and Cu+Cu

For the same For the same collision system collision system size (Nsize (Npartpart) dN) dNchch/d/d

shape is very shape is very similar forsimilar for central Cu+Cu with central Cu+Cu with

mid-central Au+Au mid-central Au+Au collisionscollisions

mid-central Cu+Cu mid-central Cu+Cu with peripheral with peripheral Au+Au collisionsAu+Au collisions

200 GeV

Cu+CuPreliminary

3-6%, Npart = 100

central

Au+Au35-40%, Npart = 99

dN/d distribution

Cu+CuPreliminary

15-25%, Npart = 61Au+Au45-55%, Npart = 56

midcentral



Comparison of Au+Au, d+Au and Comparison of Au+Au, d+Au and p+p collisions at 200 GeVp+p collisions at 200 GeV

Scale by NScale by Npartpart/2/2 allows for a direct allows for a direct

comparison to p+pcomparison to p+p i.e. normalized to 1 i.e. normalized to 1

participating pairparticipating pair

Multiplicity obtained at the Multiplicity obtained at the same center-of-mass same center-of-mass energy is similar in p+p energy is similar in p+p and d+Auand d+Au

Multiplicity is larger for Multiplicity is larger for Au+Au collisions at the Au+Au collisions at the same energysame energy

All at √s = 200 GeV

dN/d distribution

d+Au : PRL 93, 082301 (2004)



Comparison of d+Au and p+pComparison of d+Au and p+p

More detailed More detailed comparison of d+Au comparison of d+Au and p+p showsand p+p shows More peripheral More peripheral

collisions tend toward collisions tend toward p+p shapep+p shape

dN/d distribution

2

dN

ch

Npa

rt

dη

-6 -4 -2 0 2 4 6 η

PHOBOS d+Au and p+pData at √s = 200 GeV

0

1

2

3

d+Au : PRC 72, 031901 (2005)p+p : 2004 J.Phys.G 30 S1133-1137

factorizationfactorization

at midrapidityat midrapidity

in energy and centralityin energy and centrality



Au+Au

PHOBOS

Cu+Cupreliminary

Au+Au

PHOBOS

200 GeV (UA5)

90 % C.L.

19.6 and 62.4 GeV (ISR)

Mid-rapidity factorization

Measured pseudorapidity density per Measured pseudorapidity density per participant pair as a function of Nparticipant pair as a function of Npartpart

0-50% cross-section0-50% cross-section

Mid-rapidity dNMid-rapidity dNchch/d/d Information about the Information about the

created matter →energy created matter →energy densitydensity

Particle production in Particle production in A+A: interplay between A+A: interplay between collision centrality collision centrality (geometry) and collision (geometry) and collision energy?energy?

balance of binary/soft balance of binary/soft processesprocesses

Au+Au : PRC 74, 021901 (2006)



Midrapidity RatiosMidrapidity Ratios

200/19.6

200/62.4

200/130Cu+Cupreliminary

Au+Au

PHOBOS

HIJING

Saturation

Data ratio 200/X Data ratio 200/X no centrality (geometry) no centrality (geometry)

dependencedependence

Models Models HIJING HIJING

disagrees with datadisagrees with data

Saturation Model Saturation Model (KLN) (KLN)

flat centrality flat centrality dependence as in datadependence as in data

Mid-rapidity factorization

KLN

HIJING:Comput.Phys.Commun. 83 (1994) 307,v 1.35KLN: Phys.Lett.B523 79 (2001) & arXiv:hep-ph/0111315

Au+Au : PRC 74, 021901 (2006)

factorizationfactorization

at midrapidityat midrapidity

versus pversus pTT



Transverse Momentum Transverse Momentum FactorizationFactorization

So far discussed So far discussed factorization of bulk factorization of bulk mattermatter ~p~pTT<1GeV/c<1GeV/c

Can look at Can look at differential differential factorization for pfactorization for pTT

binsbins

pT factorization



Au+AuCu+Cu

Au+Au: PRL 94, 082304 (2005)

<pT> = 0.25 GeV/c <pT> = 1.25 GeV/c <pT> = 2.5 GeV/c <pT> = 3.38 GeV/c <pT> = 3.88 GeV/c

Ratio of charged hadron yields inRatio of charged hadron yields in 200 and 62.4 GeV 200 and 62.4 GeV factorization up to pfactorization up to pTT ≈ 4 GeV/c for N ≈ 4 GeV/c for Npartpart > 40 > 40

pT factorization




SummarySummaryPHOBOS has measured multiplicity forPHOBOS has measured multiplicity for

large systematic dataset large systematic dataset -5.4<η<5.4-5.4<η<5.4 2 to 360 participants2 to 360 participants √√s = 19.6 to 200 GeVs = 19.6 to 200 GeV

Au+Au and Cu+Cu data are similar at the same NAu+Au and Cu+Cu data are similar at the same Npartpart

Scaling and factorization properties are found in the Au+Au Scaling and factorization properties are found in the Au+Au datadata

extended longitudinal scalingextended longitudinal scaling mid-rapidity factorization in bulk yield and versus pmid-rapidity factorization in bulk yield and versus pTT seem to persist into the Cu+Cu collision systemseem to persist into the Cu+Cu collision system

Observed factorization in energy and centrality is seen in Observed factorization in energy and centrality is seen in multiplicity and versus pmultiplicity and versus pTT

implies that this is set at an early stage of the collision and is implies that this is set at an early stage of the collision and is connected with the geometry of the collisionconnected with the geometry of the collision

The EndThe End



Ratio of yield forRatio of yield for 200 and 62.4 GeV is centrality 200 and 62.4 GeV is centrality independent for all measured pindependent for all measured pTT bins bins


pT factorization

Data from PRL 94, 082304 (2005)

Documents

Charged Particle Multiplicities from Cu+Cu, Au+Au and d+Au Collisions at RHIC