for the Collaboration

Charged Hadron Spectra and Ratios in d+Au and

Au+Au Collisions from PHOBOS Experiment at RHIC

Adam TrzupekThe Henryk Niewodniczański Institute of Nuclear Physics

Polish Academy of Sciences

Kraków, Poland

4th Budapest Winter School on Heavy Ion Collisions(December 1st-3rd 2004) in Budapest, Hungary

nucl-ex/0410022, 2004

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

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

Zhengwei Chai, Patrick Decowski, Edmundo García, Tomasz Gburek, Nigel George,

Kristjan Gulbrandsen, Steve Gashue, Clive Halliwell, Joshua Hamblen, Adam Harington,

Michael Hauer, George Heintzelman, Conor Henderson, David Hofman, Richard Hollis,

Roman Holynski, Burt Holzman, Aneta Iordanova, Erik Johnson, Jay Kane, Judith Katzy,

Nazim Khan, Wojtek Kucewicz, Piotr Kulinich, Chia Ming Kuo, Jang Wo Lee, Willis Lin,

Steven Manly, Don McLeod, Alice Mignerey, Rachid Nouicer , Gerrit van Nieuwenhuizen,

Andrzej Olszewski, Robert Pak, Inkyu Park, Heinz Pernegger, Corey Reed, Louis Remsberg,

Mike Reuter, Christof Roland, Gunther Roland, Leslie Rosenberg, Joe Sagerer, Pradeep Sarin,

Paweł Sawicki, Helen Seals, Iouri Sedykh, Wojtek Skulski, Chadd Smith, Maciej Stankiewicz,

Peter Steinberg, George Stephans, Andrei Sukhanov, Jaw-Luen Tang, Marguerite Belt Tonjes,

Adam Trzupek, Carla Vale, Robin Verdier, Gábor Veres, Edward Wenger, Frank Wolfs,

Barbara Wosiek, Krzysztof Wozniak, Alan Wuosmaa, Bolek Wyslouch, Jinlong Zhang

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

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

PHOBOS Collaboration

PHOBOS Detector

T0 counter

Spectrometer

SpecTOF

TOF

multiplicity, vertex and calorimeter detectors are not labeled(see Russell Betts talk)

Magnet

Paddle Trigger counter

Paddle Trigger counter

T0 counter

• pT = 0.2 - ~5 GeV/c track curvature in B field => p,charge dE/dx in Si, ToF => mass

• pT = 0.03 - 0.2 GeV/c low-p particles stop in silicon wafers => p, mass

B field negligible => no charge identification

pT and PID Measurement in PHOBOS Spectrometer

10 cm

z

-x

PHOBOS Spectrometer• dipole magnetic field of 2T at maximum• 16 layers of silicon wafers• fine/optimal pixelization, precise dE measurement• collision vertex close to spectrometer• near mid-rapidity coverage

70 cm

0 10 20 Z [cm]

X[c

m]

AB

CD

EF

Be pipe

. .

PID Measurement in PHOBOS Spectrometer<

dE

/dx>

pT > 0.2 GeV/c pT = 0.03 - 0.2 GeV/c

Etot = dEi , i=A, ... ,E

Mpi = Ei dEi/dx

Mp = < Mpi >

/K separation: pT < ~0.6 GeV/cp(p) separation: pT < ~1.2 GeV/c

Kp

Energy Dependence of Antiparticle to Particle Ratios

p/p

K–/K+

A+A central, near mid-rapidity PHOBOS 130 GeV

PRL 87 (2001) 102301

PHOBOS 200 GeV

PRC 67 (2003) 0211901

particle ratios increase with energy

net baryon density is rapidly decreasing

GOOD CONDITIONS FOR QGP FORMATION

at sNN = 200 GeV in Au+Au central collisions:

baryochemical potential: B = 27 2 MeV

energy density: = ~ 5 GeV /fm3 , 0 = 1 fm, nucl-ex/0410022

in AA collisions “BULK” of hadrons is produced at low transverse momentum “TAIL” of transverse momentum distribution at high-pT originates from hard partonic scatterings

0.2<y<1.4

Charged Hadron Transverse Momentum Distributions in Au+Au collisions at sNN = 200 GeV

centrality: 0-15%mid-rapidity

PRC RC in press nuc-ex/0401006 PLB 578 (2004) 297

PLB 578 (2004) 297

TAIL

BULK

invariant yieldsparticle density

parton

nucleus

t = - a few fm/c

parton

t = 0 fm/c

hard partonicscattering

t = + a few fm/c

hadronization

jet of hadrons

leading hadron of high pT

t = + a few fm/c

scattered partons pass throughhot and densemedium

Hard partonic scatterings occur early in AA collision. Scatteredpartons can probe the dense and hot medium created in AA collision

detector

nucleus

if scattered partons loose energy then the numberof leading hadrons will be suppressed (”jet quenching”)

High-pT Probes

RAA

„hard collisions”

„soft collisions”

pT(GeV/c)

Nuclear Modification Factor RAA

ddpNdN

ddpNdidsbpR

TNN

coll

TAA

TAA /

/,...),,,,(

2

2

RAA=1 (Ncoll scaling), lack of nuclear effects, small cross section for hard partonic scattering

Ncoll - number of binary inelastic NN interactions in AA

,m,

NN data:p+ p (UA1) at 200 GeVp+ p (ISR) at 62.4 GeV

RAuAu for Charged Hadrons in Au+Au Collisions at sNN = 200 GeV

Ncoll scaling

suppression of high-pT hadron production is observed

strongest effect is seen in most central collisions

PLB 578 (2004) 297

pT (GeV/c)

45-50% 35-45%

25-35% 15-25%

6-15% 0-6%

RAuAu

mid- peripheral

central

1 d2 NAuAu / dpTd

<Ncoll> d2 NNN / dpTd

RAuAu =

High-pT Suppression

Final state effects?

energy loss in medium

initial state effects possible in d+Auno final state effects

no suppression in d+Au collisions indicates that final state effects are responsible for suppression in Au+Au

central Au+Au:

d +Au:

Initial state effects?

gluon saturation:suppression of high parton density (g+g-> g)Color Glass Condensate

d+Au at 200 GeV is a control experiment

RdAu for Charged Hadrons, sNN = 200 GeV

d+Au control experiment indicates that suppression of particle production in central Au+Au collisions at sNN = 200 GeV

is a consequence of final state effects

PRL 91 (2003) 072302

RdAu

Au+Au

mid-rapidity, 0.2<y<1.4

medium created in Au+Au collisions is strongly interacting

no suppression in d+Au collisions

Low-pT Spectra of Identified Charged Particles in Central Au+Au at sNN = 200 GeV

12

1)/exp(1

21 BET

TT

TmAdydm

Ndm

mT = pT2+mh

2

no enhancement in low-pT yields for pions is observed flattening of (p+p) spectra down to very low pT, consistent with transverse expansion of the system

|T= 229 MeV for (++-) 293 MeV for (K++ K

-)

392 MeV for (p + p)

PRC RC in pressnucl-ex/0401006

medium created in Au+Au collisions is strongly interacting

RAuAu for Charged Hadrons at sNN = 62.4 GeV

nucl-ex/0405003 (Au+Au, 62.4 GeV)

RHIC Physics Run 2004

RAuAu at 62.4 GeV is significantly higher than at 200 GeV for all centralities within the studied pT range

RA

uA

u

Energy Dependence of RAA

nucl-ex/0405003

central Pb+Pb and Au+Au collisions, near mid-rapidity

at high-pT: RAA > 1 at sNN = 17.2 GeV

RAA < 0.2 at sNN = 200 GeV

smooth evolution of RAA with energy

pT(GeV/c)yields normalized by Npart weakly depend on centrality

Nuclear Modification Factor RAANpart

0 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4

Ncoll scaling

45-50% 25-35% 15-25% 0-6%

Npart - number of participating (wounded) nucleons in AA

<Ncoll>

<Npart>

b(fm)

Au+AuGlauber Model

Ncoll ~ Npart 4/3

nucl-ex/0405003, Au+Au: 62.4 GeV, 200 GeV

1 d2 NAA / dpTd <Npart/2> d2 NNN/ dpTdRAA

Npart =

yield per participant (or RAANpart) changes by less than 25% for both

energies in centrality range from 60 to 340 participants.

centrality evolution is the same at both energies:

RAANpart = RPC

Npart (Npart) * f(sNN )

Factorization of Energy and Centrality Dependence of RAA

Npart at sNN = 62.4 and 200 GeV

nucl-ex/0405003

SummaryAu+Au: • almost net-baryon free environment, energy density ~ 5 GeV/fm3

• strong suppression of high-pT charged hadron yields in central collisions at 200 GeV (~ 5 times at pT ~ 5 GeV)

• no evidence for enhanced production of very low-pT pions• flattening of p+p spectra at low-pT, strong radial flow in the system, • RAuAu at 62.4 GeV is significantly higher than RAuAu at 200 GeV• factorization of energy and centrality dependence of RAuAu

Npart

• approximate Npart scaling of hadron yields

d+Au:• no suppression of charged hadron yields at high-pT (at mid-rapidity)

suppression in central Au+Au is final state effect

Conclusions

STRONGLY INTERACTING, HIGH DENSITY AND ALMOST NET-BARYON FREE

MEDIUM IS CREATED AT THE HIGHEST RHIC ENERGY IN CENTRAL Au+Au COLLISIONS

particle ratios high-pT suppression low-pT spectra

Triggering on Collisions & Centrality

• Coincidence between Paddle counters at t = 0 defines a valid collision

• Paddle + ZDC timing reject background

PP

Negative

Paddles

Positive Paddles

Aux

z

PN

Positive ZDC

Negative ZDC

NegativeCerenkov

PositiveCerenkov

Au

Central Peripheral

HIJING +GEANT Glauber calculation Model of paddle trigger

Data Data+MC

RdAu as a Function of Pseudo-rapidity( = - ln tan(/2))

nucl-ex/0406017, PRC in press nucl-ex/0406017, PRC in press

positive is in deuteron direction with increasing , RAA decreasesmodel constraints: Color Glass Condensate

PRC in pressnucl-ex/0401006

d+Au

Scale uncertainty: 15%

Not feed-down corrected

Au+Au Spectra normalized at 2 GeV/c

mT Scaling in d+Au vs Au+Au

RAA at low energy (fixed target experiments)

Initial state effects

RSAu

RPbPb

RpA

Cronin effect

Elab = 200 AGeV, sNN = 19.4GeV

Pb+Pb: Elab =158 AGeV, sNN = 17.3 GeV

RSS

multiple scatterings

pT broadening => RAA

>1

Factorization of RAA(sNN,centrality)

TNNTcollNPC

NAA p,sfp,NRR collcoll For b<10.5 fm:

ddp/Nd

ddp/Nd

N

NR

TcentAA

2TAA

2

coll

centcollN

PCcoll

Centrality Ncoll

62.4 GeV200 GeV

pT (GeV/c)

nucl-ex/0405003

EPS2003 - Aachen 38

Theory Calculations

Cronin Effect:X.N. Wang, Phys. Rev C61, 064910 (2000).

Attributed to initial state multiple scattering.Implemented by Q2(pt) dependent Gaussian kt broadening

Energy loss applied:M. Gyulassy, I. Vitev, X.N Wang and B.W. Zhang; nucl-th/0302007

dE/dxo is the only free parameter.It is determined by fitting toSTAR central RAA(pt)