RHIC PHENOMENOLOGY AS SEEN BY

Wit Busza

QCD in the RHIC Era

UCSB, April 2002

The PHOBOS CollaborationBirger Back, Alan Wuosmaa

Mark Baker, Donald Barton, Alan Carroll, Nigel George, StephenGushue, George Heintzelman, Burt Holzman, Robert Pak, LouisRemsberg, Peter Steinberg, Andrei Sukhanov

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

Maarten Ballintijn, Wit Busza (Spokesperson), Patrick Decowski,Kristjan Gulbrandsen, Conor Henderson, Jay Kane, Judith Katzy,Piotr Kulinich, Heinz Pernegger, CoreyReed, Christof Roland, Gunther Roland, Leslie Rosenberg, PradeepSarin, Stephen Steadman, George Stephans, Gerrit vanNieuwenhuizen, Carla Vale, Robin Verdier, Bernard Wadsworth,Bolek Wyslouch

Willis Lin, ChiaMing Kuo

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

Russell Betts, Edmundo Garcia, Clive Halliwell, David Hofman,Wojtek Kucewicz, Don McLeod, Rachid Nouicer, Michael Reuter

Richard Bindel, Edmundo Garcia, Alice Mignerey

ARGONNE NATIONAL LABORATORY

BROOKHAVEN NATIONAL LABORATORY

INSTITUTE OF NUCLEAR PHYSICS, KRAKOW

MASSACHUSETTS INSTITUTE OF TECHNOLOGY

NATIONAL CENTRAL UNIVERSITY, TAIWAN

UNIVERSITY OF ROCHESTER

UNIVERSITY OF ILLINOIS AT CHICAGO

UNIVERSITY OF MARYLAND

PHOBOS Detector

0 +3.1-3.1 +5.4-5.4

4 Multiplicity:

Two-arm Spectrometer:

Number of Participants

pA:

AA:

Participants Npart

SpectatorsNpart=+1

Estimating the Number of Participants

• Assumption:– Multiplicity is monotonic with Npart– Glauber model applicable

• Nucleons maintain same cross-section

Model

Charged Particle Multiplicity 130 GeV AuAu 200 GeV AuAu

25-35%cent

0-6%cent

45-55%cent

Ntot

= 4100 ±210 Ntot

= 4960 ±250

dN/d

d

d n

n

1

)GeV(s24 31 5345 63

2-4

5-9

10-1

415

-19

20-2

4T

otal

obs

erve

d m

ultip

licity

W. Thome et al.,Nucl. Phys. B129(1977) 365.

130 GeV AuAu 200 GeV AuAu

25-35%cent

0-6%cent

45-55%cent

dN

/d

ISR data

Compilation of p-emulsion data

Limiting fragmentation in pA, Ap and pp scattering

pA

Ap

pp

Collision Viewed in Rest Frame of One Projectile

UA5, Z.Phys.C33, 1 (1986)

Limiting Fragmentation is seen

Reduction of Target Fragments with Centrality ?200 GeV AuAu

NA5 DeMarzo, et al (1984)

From Barton et al

pA pX

pA pi-X

XF

With one exception, the pp, pA and AA data in the fragmentation region are consistent with the following picture:

1. A “wall of gluons” strips the gluons from the target nucleons. This process is independent of the energy of the incident nucleus.

2. The number of remaining quarks is only weakly dependent on the thickness of the incident nucleus.

3. The quarks fragment into the particles detected in the fragmentation region. Some rescattering occurs.

Au+Au & pp at 200 GeV

From W. Busza (1976)

From Peter Steinberg

Most central

RHIC : PHOBOS AuAu s = 200 GeV

SPS : EMU-13 PbPb s = 17 GeV RHIC : PHOBOS AuAu s = 130 GeV 200 GeV AuAu

Collision Viewed in Center of Mass Frame

AuAu normalized to equivalent number of participants

fpp(s) =(CDF/UA5)

Central Au+Au p+p

PRL 87 (2001) 11

45

1000~all

d

dN

GeVE 1~

32 200~)1(~ fmfmR

Total energy released ~2000GeV

Max. initial overlap volume

At 200 GeV initial released energy density 3/10 fmGeV

Centrality Dependence of dN/deta

• Naïve expectations:– Consider collision of two

“tubes of nucleons”

ddN

2/partNddN

1 6 or 36?

1 or 6?1

2/partbinary NNNote:

= Avg number of collision each participant makes (~6 for central AuAu)

Au+Au & pp at 200 GeV

From Peter Steinberg

Au+Au & pp at 200 GeV

Azimuthal Angular Distributions

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

b (reaction plane)

Look at emission patterns using Fourier expansion: extract V2 components from the fits.

“head on” view of colliding nuclei

y

x

Centrality Dependence of v2

Hydrodynamic model

Elli

pti

c flow

, v

2

Normalized Paddle Signal

Systematic error ~ 0.007

SPS

AGS

Preliminary

Preliminary || < 1.0 sNN=130GeV

Peripheral Collisionsb

Central Collisionsb

V2 (elliptical flow) vs

• Averaged over centrality

• V2 drops for || > 1.5

• Dependence on appears to be different than at lower energy.

V2PHOBOS Preliminary STAR (PRL)

00.010.020.030.040.050.060.070.08

0 1 2 3 4 5 6

SPS NA49 (QM99)

rapidity

Pion (b<11fm)

PHOBOS Systematic error ~ 0.007

sNN= 130 GeV sNN= 17 GeV

All Charged

Min. bias

AuAu130 GeV

Stat. Syst.

06.004.060.0

06.007.091.0

02.001.000.1

p

p

K

K

)(03.0)(02.074.0

)(04.0)(03.095.0

)(020.0)(006.0025.1

sysstatp

p

sysstatK

K

sysstat

Preliminary 200GeV AuAu

Energy Dependence of Baryo-chemical potential B

Nucl. Phy. A697: 902-912 (2002)

Baryon Stopping

From W.B and A.S.Goldhaber

•PHOBOS web-site: www.phobos.bnl.gov

•Published Physics Results

–Charged particle multiplicity near mid-rapidity in central Au+Au collisions at 56 and 130 GeV Phys. Rev. Lett. 85, 3100 (2000)

–Ratios of charged antiparticles-to-particles near mid-rapidity in Au+Au collisions at 130 GeV Phys. Rev. Lett. 87, 102301 (2001)

–Charged-particle pseudorapidity density distributions from Au+Au collisions at 130 GeV Phys. Rev. Lett. 87, 102303 (2001)  

–Energy dependence of particle multiplicities near mid-rapidity in central Au+Au collisions Phys. Rev. Lett 88, 22302(2002)

–Centrality Dependence of Charged Particle Multiplicity at | in Au+Au Collisions at 130 GeV Phys. Rev. C65, 031901(R)(2002)

–Centrality Dependence of Charged Particle Multiplicity at |<1 in Au+Au Collisions at 130 and 200 GeV Submitted to Phys. Rev. C (2002)    

Conclusions based on PHOBOS Results

• Central rapidity density increases approximately logarithmically with energy. Why?

It is lower than most pre-RHIC predictions. Initial Energy Density > 10GeV/fm3

• Eliptic Flow suggests high pressure is created.

dN/dn is boost invariant for +- 2 units of rapidity about zero, but not eliptic flow. Why?

• Fragmentation of incident states essentially as expected.

Rapidity distribution per participant for AuAu and p pbar have similar shape over entire pseudo rapidity range. The former is approximately 1.3 times the later. This scaling is not understood.

• Many features of AuAu multiparticle production are well reproduced by saturation model of Kharzeev et al.

• No surprises in particle ratios.

• To understand multiparticle production, need energy scan and species scan.