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Charged Hadron Spectra and Ratios in d+Au and Au+Au Collisions from PHOBOS Experiment at RHIC. nucl-ex/0410022, 2004. Adam Trzupek The Henryk Niewodniczański Institute of Nuclear Physics Polish Academy of Sciences Kraków, Poland. for the Collaboration.

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Charged hadron spectra and ratios in d au and au au collisions from phobos experiment at rhic
Charged Hadron Spectra and Ratios in d+Au and Au+Au Collisions from PHOBOS Experiment at RHIC

nucl-ex/0410022, 2004

Adam Trzupek

The Henryk Niewodniczański Institute of Nuclear Physics

Polish Academy of Sciences

Kraków, Poland

for the Collaboration

4th Budapest Winter School on Heavy Ion Collisions

(December 1st-3rd 2004) in Budapest, Hungary


Phobos collaboration
PHOBOS Collaboration Collisions from PHOBOS Experiment at RHIC

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 LABORATORY

INSTITUTE OF NUCLEAR PHYSICS PAN, KRAKÓW MASSACHUSETTS INSTITUTE OF TECHNOLOGY

NATIONAL CENTRAL UNIVERSITY, TAIWAN UNIVERSITY OF ILLINOIS AT CHICAGO

UNIVERSITY OF MARYLAND UNIVERSITY OF ROCHESTER


PHOBOS Detector Collisions from PHOBOS Experiment at RHIC

TOF

SpecTOF

T0 counter

Paddle Trigger

counter

Spectrometer

Magnet

Paddle Trigger

counter

multiplicity, vertex and calorimeter

detectors are not labeled

(see Russell Betts talk)

T0 counter


P t and pid measurement in phobos spectrometer

z Collisions from PHOBOS Experiment at RHIC

-x

F

E

D

C

X[cm]

B

A

.

.

Be pipe

01020Z [cm]

.

pT and PID Measurement in PHOBOS Spectrometer

70 cm

  • 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

10 cm

  • 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-pparticles stop

  • in silicon wafers => p, mass

  • B field negligible => no charge identification


Pid measurement in phobos spectrometer
PID Measurement in PHOBOS Spectrometer Collisions from PHOBOS Experiment at RHIC

pT > 0.2 GeV/c

pT = 0.03 - 0.2 GeV/c

p

K

<dE/dx>

Etot =  dEi , i=A, ... ,E

Mpi= Ei dEi/dx

Mp = < Mpi >

/K separation: pT < ~0.6 GeV/c

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


Energy dependence of antiparticle to particle ratios

Collisions from PHOBOS Experiment at RHICPHOBOS 130 GeV

PRL 87 (2001)102301

PHOBOS 200 GeV

PRC 67 (2003) 0211901

Energy Dependence of Antiparticle to Particle Ratios

A+A central, near mid-rapidity

K–/K+

p/p

particle ratios increase with energy

net baryon density is

rapidly decreasing

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

baryochemical potential:B = 27  2 MeVenergy density:  =~ 5 GeV /fm3 , 0 = 1 fm, nucl-ex/0410022

GOOD CONDITIONS FOR QGP FORMATION


Charged Hadron Transverse Momentum Distributions Collisions from PHOBOS Experiment at RHIC

in Au+Au collisions at sNN = 200 GeV

particle density

invariant yields

BULK

centrality: 0-15%

mid-rapidity

 PRC RC in press

nuc-ex/0401006

PLB 578 (2004) 297

TAIL

0.2<yp<1.4

PLB 578 (2004) 297

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


High-p Collisions from PHOBOS Experiment at RHICT Probes

Hard partonic scatterings occur early in AA collision. Scattered

partons can probe the dense and hot medium created in AA collision

t = - a few fm/c

t = 0 fm/c

t = + a few fm/c

t = + a few fm/c

nucleus

nucleus

parton

parton

hard partonic

scattering

scattered partons

pass through

hot and dense

medium

hadronization

jet of hadrons

if scattered partons loose energy then the number

of leading hadrons will be suppressed (”jet quenching”)

leading hadron

of high pT

detector


Nuclear modification factor r aa
Nuclear Modification Factor R Collisions from PHOBOS Experiment at RHICAA

,m,

Ncoll - number of binary inelastic NN interactions in AA

NN data:

p+ p (UA1) at 200 GeV

p+ p (ISR) at 62.4 GeV

RAA

„hard collisions”

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

„soft

collisions”

pT(GeV/c)


R Collisions from PHOBOS Experiment at RHICAuAu for Charged Hadrons in Au+Au Collisions

at sNN = 200 GeV

PLB 578 (2004) 297

1 d2 NAuAu/ dpTd

RAuAu=

45-50%

35-45%

RAuAu

<Ncoll> d2 NNN/ dpTd

Ncoll scaling

mid- peripheral

25-35%

15-25%

0-6%

6-15%

central

pT (GeV/c)

suppression of high-pT hadron production is observed

strongest effect is seen in most central collisions


High p t suppression
High-p Collisions from PHOBOS Experiment at RHICT Suppression

central Au+Au:

Final state effects?

Initial state effects?

gluon saturation:

suppression of high parton density (g+g-> g)

Color Glass Condensate

energy loss in medium

d +Au:

initial state effects possible in d+Au

no final state effects

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

d+Au at 200 GeV is a control experiment


R Collisions from PHOBOS Experiment at RHICdAufor Charged Hadrons, sNN = 200 GeV

mid-rapidity, 0.2<y<1.4

PRL 91 (2003) 072302

no suppression in d+Au collisions

RdAu

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

Au+Au

medium created in Au+Au collisions is strongly interacting


Low p t spectra of identified charged particles in central au au at s nn 200 gev

m Collisions from PHOBOS Experiment at RHICT = pT2+mh2

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

PRC RC in press

nucl-ex/0401006

|T= 229 MeV for (++-)

293 MeV for (K++ K-)

392 MeV for (p + p)

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

medium created in Au+Au collisions is strongly interacting


R Collisions from PHOBOS Experiment at RHICAuAu for Charged Hadrons at sNN = 62.4 GeV

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

RHIC Physics Run 2004

RAuAu

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


Energy dependence of r aa

at high-p Collisions from PHOBOS Experiment at RHICT:

Energy Dependence of RAA

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

nucl-ex/0405003

smooth evolution of RAA with energy

RAA > 1 at sNN = 17.2 GeV

RAA < 0.2 at sNN = 200 GeV


Nuclear Modification Factor R Collisions from PHOBOS Experiment at RHICAANpart

<Ncoll>

Au+Au

Glauber Model

1 d2 NAA / dpTd

RAANpart=

<Npart/2> d2 NNN/ dpTd

Ncoll ~ Npart4/3

<Npart>

b(fm)

Npart - number of participating (wounded) nucleons in AA

nucl-ex/0405003, Au+Au: 62.4 GeV,

 200 GeV

Ncoll scaling

45-50%

25-35%

15-25%

0-6%

pT(GeV/c)

yields normalized by Npart weakly depend on centrality

0 1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4


Factorization of energy and centrality dependence of r aa npart at s nn 62 4 and 200 gev
Factorization of Energy and Centrality Dependence Collisions from PHOBOS Experiment at RHICof RAANpartat sNN = 62.4 and 200 GeV

nucl-ex/0405003

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 = RPCNpart (Npart) * f(sNN )


Summary
Summary Collisions from PHOBOS Experiment at RHIC

Au+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 RAuAuNpart

  • 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
Conclusions Collisions from PHOBOS Experiment at RHIC

particle ratios high-pT suppression low-pT spectra

STRONGLY INTERACTING, HIGH DENSITY

AND ALMOST NET-BARYON FREE

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


Triggering on collisions centrality

Positive Paddles Collisions from PHOBOS Experiment at RHIC

Negative Paddles

NegativeCerenkov

PositiveCerenkov

Negative ZDC

Positive ZDC

Au

Au

PN

PP

x

z

Triggering on Collisions & Centrality

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

  • Paddle + ZDC timing reject background

Data

Data+MC

  • HIJING +GEANT

    • Glauber calculation

    • Model of paddle trigger

Peripheral

Central


R dau as a function of pseudo rapidity ln tan 2
R Collisions from PHOBOS Experiment at RHICdAu 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 decreases

model constraints: Color Glass Condensate


M t scaling in d au vs au au
m Collisions from PHOBOS Experiment at RHICT Scaling in d+Au vs Au+Au

PRC in press

nucl-ex/0401006

Au+Au

Spectra

normalized

at 2 GeV/c

d+Au

Scale uncertainty: 15%

Not feed-down corrected


R aa at low energy fixed target experiments

E Collisions from PHOBOS Experiment at RHIClab= 200 AGeV, sNN = 19.4GeV

RSAu

RAA at low energy (fixed target experiments)

Pb+Pb: Elab=158 AGeV, sNN = 17.3 GeV

RPbPb

RSS

RpA

multiple scatterings

pT broadening => RAA >1

Cronin effect

Initial state effects


Factorization of r aa s nn centrality

62.4 GeV Collisions from PHOBOS Experiment at RHIC

200 GeV

Factorization of RAA(sNN,centrality)

For b<10.5 fm:

Centrality  Ncoll

pT (GeV/c)

nucl-ex/0405003


Theory Calculations Collisions from PHOBOS Experiment at RHIC

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 to

STAR central RAA(pt)

Cronin Effect:

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

Attributed to initial state multiple scattering.

Implemented by Q2(pt) dependent Gaussian kt broadening

EPS2003 - Aachen

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