Centrality Dependence of Charged Hadron Production at RHIC

d+Au vs Au+Au

Gunther Roland/MITfor the

PHOBOS Collaboration

BNL June 18, 2003

Collaboration

Birger Back, Mark Baker, Maarten Ballintijn, Donald Barton, Bruce Becker, Russell Betts,

Abigail Bickley, Richard Bindel, Andrzej Budzanowski, Wit Busza (Spokesperson), Alan Carroll,

Patrick Decowski, Edmundo Garcia, Tomasz Gburek, Nigel George, Kristjan Gulbrandsen,

Stephen Gushue, Clive Halliwell, Joshua Hamblen, Adam Harrington, Conor Henderson,

David Hofman, Richard Hollis, Roman Holynski, Burt Holzman, Aneta Iordanova, Erik Johnson,

Jay Kane, Nazim Khan, Piotr Kulinich, Chia Ming Kuo, Jang Woo Lee, Willis Lin, Steven Manly,

Alice Mignerey, Gerrit van Nieuwenhuizen, Aaron Noell, Rachid Nouicer, Andrzej Olszewski,

Robert Pak, Inkyu Park, Heinz Pernegger, Corey Reed, Louis Remsberg, Christof Roland,

Gunther Roland, Joe Sagerer, Pradeep Sarin, Pawel Sawicki, Iouri Sedykh, Wojtek Skulski,

Chadd Smith, Peter Steinberg, George Stephans, Andrei Sukhanov, Ray Teng,

Marguerite Belt Tonjes, Adam Trzupek, Carla Vale, Robin Verdier, Gábor Veres, Bernard

Wadsworth, Frank Wolfs, Barbara Wosiek, Krzysztof Wozniak, Alan Wuosmaa, Bolek Wyslouch,

Jinlong Zhang

ARGONNE NATIONAL LABORATORY BROOKHAVEN NATIONAL LABORATORYINSTITUTE OF NUCLEAR PHYSICS, KRAKOW MASSACHUSETTS INSTITUTE OF TECHNOLOGYNATIONAL CENTRAL UNIVERSITY, TAIWAN UNIVERSITY OF ILLINOIS AT CHICAGO

UNIVERSITY OF MARYLAND UNIVERSITY OF ROCHESTER

PHOBOS preliminaryAu+Au 200 GeV15% central

How to connect observedfinal state particles to theory of strong interaction?

?

Rapidity Density600 1200Compilation by K. Eskola

Particle Multiplicity at RHIC

Particle Multiplicity at RHIC

Rapidity Density600 1200

PHOBOS Central Au+Au (200 GeV)

Compilation by K. Eskola

PHOBOS multiplicity papers:

Phys. Rev. Lett. 85 , 3100 (2000)

Phys. Rev. Lett. 87, 102303 (2001)

Phys. Rev. C 65 , 31901R (2002)

Phys.Rev. Lett. 88 , 22302 (2002)Phys. Rev. C 65 , 061901R (2002) nucl-ex/0210015, PRL in Pressnucl-ex/0301017, subm. to PRL

• Multiplicity at low end of range– But: Energy density 30x nuclear matter

• Most models didn’t do so well

Parton Saturation

Low Energy

High Energy

Particle Multiplicity at RHIC

Rapidity Density600 1200

PHOBOS Central Au+Au (200 GeV)

Compilation by K. EskolaColor Glass

Rapidity Density600 1200

PHOBOS Central Au+Au (200 GeV)

Compilation by K. EskolaColor Glass

Hadron multiplicities at RHIC well

described by Parton Saturation

Particle Multiplicity at RHIC

Kharzeev & Levin, Phys. Lett. B523 (2001) 79

Data: PHOBOS,Phys. Rev. Lett. 87, 102303 (2001)

pT Spectra for Au+Au @ 200 GeV

0.2<y<1.4

Data: PHOBOS, nucl-ex/0302015Submitted to Phys Lett B

Relative to UA1 p+p

Centrality Dependence vs pT

PHOBOS, nucl-ex/0302015

Similar centrality dependence atpT = 0.5 and 4 GeV/c !

Initial StateCoherence?

Interaction in Dense Medium?

Predictions for d+Au

Vitev, nucl-th/0302002, Phys.Lett.B in press Vitev and M.Gyulassy, Phys.Rev.Lett. 89 (2002)

Central

Peripheral

Kharzeev, Levin, McLerran, hep-ph/021332

“~30%suppression of high pT particles”(central vs peripheral)

16% increase central vs peripheral

Nu

clea

r M

od

ific

atio

n F

acto

r R

dA

u

Parton Saturation pQCD

PHOBOS Detector 2003

SPECTRIG

T0

T0

mini-pCal

pCal

i. Moved TOF walls back

• 5 m from interaction point

ii. New on-line high pT Spectrometer Trigger

iii. New “time-zero” (T0) Cerenkov detectors • On-line vertexing and ToF start time

iv. Forward proton calorimeters on Gold and Deuteron sides

v. DAQ upgrade (x10)

Centrality Determination in d+Au

Multiplicity distributionPseudorapidity

Glauber Calculation•Hijing 1.383

•Hulthen w.f.•41mb inelastic cross-section

•Full GEANT Simulation

HIJING Simulation

dN

/d

Co

un

ts

d+Au pT Spectra

Compare to p+p reference…

From Glauber(HIJING 1.383)

41mb (same as for Glauber)

From UA1, usingPythia to go from|| < 2.5 to 0.2 < < 1.4

…for each centrality bin

PHOBOS d+Au: nucl-ex/0306025

central Au+Au

All syst. uncertainties: 90% C.L.

PHOBOS d+Au: nucl-ex/0306025

RdAu vs pT

Centrality dependence of RdAu

Data disfavor initial state interpretation of Au+Au high-pT suppression

N.B. Smaller ppinel would increase

RdAu central vs RdAu peripheral

PHOBOS d+Au: nucl-ex/0306025

All syst. uncertainties: 90% C.L.

Initial State ‘Final State’ Interactions

Multiplicity systematicsconnected to initial state

Consistent with parton saturation picture

Interaction of fast partonswith dense medium has been observed

Quantitative diagnostic tool now established

Connection to QCD