Bulk Observables in p-p, d-Au and Au-Au at RHIC

David Hofman

University of Illinois at Chicago

For the Collaboration

QCD and High Energy Hadronic InteractionsMarch 28 – April 4, 2004

XXXIXth Recontres de Moriond

Moriond 2004 2

Collaboration (February 2004)

Birger Back, Mark Baker, Maarten Ballintijn, Donald Barton, Russell Betts, Abigail Bickley,

Richard Bindel, Wit Busza (Spokesperson), Alan Carroll, Zhengwei Chai, Patrick Decowski,

Edmundo García, Tomasz Gburek, Nigel George, Kristjan Gulbrandsen, Clive Halliwell,

Joshua Hamblen, Adam Harrington, Michael Hauer, Conor Henderson, David Hofman, Richard Hollis,

Roman Hołyński, Burt Holzman, Aneta Iordanova, 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, Helen Seals, Iouri Sedykh, Wojtek Skulski,

Chadd Smith, Maciej Stankiewicz, 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 Woźniak, Alan Wuosmaa, Bolek Wysłouch

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

Moriond 2004 3

Charged Particle Production at RHIC

670d

ch

dN@ midrapidity 200 GeV

=-ln tan /2

Pseudorapidity = = Lorentz invariant angle with

respect to the beampipe

0-1

-2

-3

+1

+2+3

dN

ch/d

Central (head-on) Collisions

Beamlinenot to scale

Moriond 2004 4

A “coffee napkin” Estimate ofEnergy Density at Midrapidity.

1000~all

d

dN

GeVE 1~

32 200~)1(~ fmfmRTotal energy released in =1 is ~ 1000 GeV

Initial Energy Density Estimate, ~ 5 GeV/fm3

Max initial overlap volume

Look at all produced particles in a Central ‘Head-on’ Collision = 1

Moriond 2004 5

Charged Particle Density near Midrapidity

RHIC - combined

Central Collisions (for Heavy Ion data)

SPS RHICAGS

√sNN (GeV)

“Logarithmic Rise” for AA data, above pp baseline

Gluon Saturation

Moriond 2004 6

Systematic Errors not shown

‘PHOBOS’ Bulk Observables ≡ Low pT

cGeVTpmeasures

ddN / 2"" general)in yields particle (charged

arXiv:nucl-ex/0401006

PHOBOS

Moriond 2004 7

Ncoll = 1

Npart/2 = 1

“Participant” Scaling

Binary “Collision” Scaling

p + p Collisions Au+Au Collisions

Npart/2 ~ A

L~A1/3

Ncoll ~ A4/3

# of participating pairs of nucleons

≡ Npart/2

# of binary NN collisions

≡ Ncoll

Moriond 2004 8

Centrality Dependence of Midrapidity Charged Particle Yields

Au+Au

0 200 4000

10

20

dN/d

/(N

pa

rt/2)

<Npart>

Au+Au Centrality Dependence allows only about 10% Ncoll Scaling

200 GeV - ||<1

peripheral central

p+p

Binary Collision(Ncoll) Scaling

Participant(Npart) Scaling

Moriond 2004 9

All RHIC energies show a similar Npart dependence

Charged Particle Production at Midrapidity

19.6 GeV preliminary

130 GeV200 GeV

Data is normalized by p+p value for each energy.

Energy and Centrality Dependence

Au+Au

p + p

peripheral central

Participant scaling

Binary collision scaling

Moriond 2004 10

Ratios to Help Cancel Systematics

Systematics Dominated by Trigger Efficiency/Centrality Determination

Systematics

Percentile of Cross Section50 40 30 20 10 0

PHOBOS, PRC 65, 061901(R) (2002)

Ratio (200/130) = 1.14 ± 0.01 (stat) ± 0.05 (syst)

Moriond 2004 11

Centrality Dependence of Total Charged Particle Production Nch

Pseudorapidity

dN

/d/

<1/

2 N

par

t>

200 GeV

19.6 GeV

central

peripheral

central

peripheral

200 GeV

130 GeV

19.6 GeV

<Nch>e+e-*(Npart/2)

Au+Au Collisions

Nch(AuAu) = (Npart/2) Nch(e+e-)

Moriond 2004 12

Pseudorapidity Distribution of Charged Particles in d + Au and p + p Collisions at 200 GeV

• p + p at 200 GeV • d + Au at 200 GeV Min-Bias

arXiv:nucl-ex/0311009 andSubmitted to PRL

PHOBOS Preliminary

PHOBOS can measure down to very low multiplicities.

Moriond 2004 13

d+Au Centrality Dependence of dNch/d Shape

In dAu, particle production shifts to negative rapidity with increasing Npart.

Systematic errors not shown

(4.2)

(15.5)

(2.7)

(7.2)

(10.8)

(Normalized to Nch so can compare shape change)

Npart

peripheral

Lines to Guide Eye Only

central

Moriond 2004 14

Participant Scaling in d+Au

Nch(dAu) = (Npart/2) Nch(pp)

Moriond 2004 15

Nch in Au-Au vs. p-p and d-Au @ 200 GeV

Difference in total charged particle production between Au+Au (e+e-) vs. d+Au (pp) at same collision energy

e+e- Au+Au

Moriond 2004 16

Features of the Data at High Pseudorapidity ().

PHOBOS Au+Au

dN

ch/d

→ Move to rest frame of one nucleus: i.e. ’ = – ybeam.

Moriond 2004 17

Reminder: Limiting Fragmentation in p+p

Data: UA5 (Alner et al.),Z.Phys.C33, 1 (1986)

p + p inel.

dN

/d

beamy Ansatz: At high collision energy, d2N/dy’dpT and particle mix, reach a limiting value and become independent of energy around beam rapidity.

Ansatz: Benecke, Chou, Yang, Yen, Phys. Rev. 188, 2159 (1969)

Moriond 2004 18

Limiting Fragmentation in Au+Au

Growth of the Fragmentation Region with sNN

Moriond 2004 19

dAu & pEmulsion per incident nucleon and approx. same Npart

Npart Selection:

p Em

1 2.4

d Au

1.6x2.41.6

Limiting Fragmentation in dAu and pEmulsion Data

Growth of the Fragmentation Region with sNN in d+Au and pEm

R. Nouicer, QM ‘04

Moriond 2004 20

Reaction plane

(R)

x

z

y

x

x (defines R)

y

zy

Charged Particle “Flow”: A Bulk Collective Effect

Initial spatial anisotropy

px

py

Final momentum anisotropy

dN/d(R ) = N0 (1 + 2v1cos (R) +

2v2cos (2(R)) + ... )

Elliptic Flow: v2

Directed Flow: v1

Moriond 2004 21

In target frame of reference, directed flow exhibits signal consistent

with limiting fragmentation

Directed Flow (v1) In Beam Rest Frame

Limiting Fragmentation Behavior in Directed FlowS. Manley, 20th Winter Workshop

Moriond 2004 22

PHOBOS Preliminary v2200

PHOBOS v2130

Elliptic Flow (v2) In Beam Rest Frame

S. Manley, 20th Winter Workshop

v2

Limiting Fragmentation Behavior in Elliptic Flow

’

Moriond 2004 23

Experimental SummaryBulk (charged particle) Observables at RHIC

• Scaling of multiplicity data with Npart/2 in Au+Au and d+Au.

• Per participant pair, Au+Au reaches e+e- total particle production level at RHIC energies. d+Au reaches p+p level (at the same collision energy).

• “Limiting fragmentation” of charged particle multiplicity yields (dN/d) observed in Au+Au and d+Au at RHIC.

• “Limiting fragmentation” of azimuthal angular distribution of charged particles (v1 and v2) observed at RHIC.