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The Experimental ChallengeSTAR ONE central Au+Au

collision at RHIC

production of MANY secondary particles

PHENIX

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“hard” probes J/, (->e+e, ) and jetsvery rare, created “early” before QGP formation, penetrate hot and

dense matter, sensitive to deconfinement • color screening in partonic phase J/suppression• energy loss in dense colored matter jet quenching, absorption

electro-magnetic radiation , e+e,

rare, emitted “any time”; reach detector unperturbed by strong final state interaction

• black body radiation initial temperature• in-medium properties of mesons chiral

symmetry restoration

hadrons , K, p frequent, produced “late” when particles stop

to interact• energy density• thermal equilibrium and collective

behavior• strangeness equilibration

Schematic View of a Heavy Ion Collision

several 1000 particles produced in central collision

b ~ 0

projectile target

p

p

cc

J

qq

ee

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Space-time Evolution of Collisions

e

space

time

Hard Scattering

AuAu

Exp

ansi

on

Hadronization

Freeze-out

jet J/

QGPThermaliztion

e+e-p K

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100% 0 %

Participants

Spectators

Spectators

Collisions are not all the same

Small impact parameter (b~0)

High energy density Large volume

Large number of produced particles

Measured as: Fraction of cross section

“centrality” Number of participants Number of nucleon-nucleon

collisions

Impact parameter

b

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Experimental Determination of Geometry

5% Central

Paddles/BBCZDC ZDC

Au Au

Paddles/BBC Central

Multiplicity Detectors

Paddle signal (a.u.)

STAR

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Experimental Program

AGS at BNL Si- and Au-beams 2 to 14.6 AGeV ~ 10 large experiments

hadronic observables all experiments SPS at CERN

S- and Pb-beams 40 to 200 AGeV 15 large experiments

charmonium NA30-NA50, NA60 (3rd generation

experiment)electromagnetic probes WA80-98, HELIOS, CERES, NA60hadronic observables all other experiments

Fixed target experiments with ion beams at two accelerators during past 20 years

experimental programs basically completed

Latest results (in particular NA60) presented at Quark Matter 2008!

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Experimental Program

Relativistic Heavy Ion Collider at BNL

Started operation in with 100 GeV beams in 2000 now in 8th year of operationAu-Au, Cu-Cu, at different energies p-p (polarized beams)d-Au

2 large experimentsPHENIXSTAR

2 experiments completedBrahmsPHOBOS

Large Hadron Collider at CERN

begins operation in 2008, first physics in 2009 One dedicated heavy ion experiment ALICE HEP experiments ATLAS & CMS with heavy ion programs

New generation of experiments at Ion Colliders

focus on PHENIX results

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Center of Mass energy measured as nucleon-nucleon equivalent

Fixed target

Examples AGS Au beam of E = 11 GeV s = 4.7 GeVSPS Pb beam of E = 160 GeV s = 17.4 GeV

Collider

Examples RHIC Au beam of E = 100 GeV s = 200 GeVLHC Pb beam of E= 2750 GeV s = 5.5 TeV

Center of Mass Energy

i.e. use nucleon mass mu ~ 939 MeV/c2

E, mu

mu 2 2 2s m Em E

E,m E,m 2s E

Highest energy densities created at colliders

Center of mass energy closely related to achievable energy density

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Relativistic Heavy Ion Collider

RHIC

STARPHENIX

PHOBOSBRAHMS

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Accelerator Complex at BNL

Two concentric rings6 interaction regions3.8 km long1740 super conducting magnets

RHIC blue and yellow rings

booster

injector

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RHIC Universal QCD Laboratory

Design Performance Au + Au p + p (polarized)

Max snn 200 GeV 500 GeV

L [cm-2 s -1 ] 8 x 1026 1.4 x 1031

Interaction rates 1.4 x 103 s -1 3 x 105 s -1

Accelerate and collide ions

from A = 1 to ~ 200

(protons polarized)

pp, pA, AA, AB

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> 600 members 52 institutions:

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STAR

Silicon Vertex Tracker

Central Trigger Barrel / TOF

FTPC

Time Projection Chamber

Barrel EM Calorimeter

Vertex Position Detectors

Endcap Calorimeter

Magnet

Coils

TPC Endcap & MWPC

RICH

FTPC

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PHENIX Physics Capabilities

2 central arms: electrons, photons, hadrons

charmonium J/, ’ ee

vector meson ee high pT

direct photons open charm hadron physics

2 muon arms: muons “onium” J/, ’, vector meson open charm

combined central and muon arms: charm production DD e

global detectors

forward energy and multiplicity event characterization

designed to measure rare probes: + high rate capability & granularity+ good mass resolution and particle ID- limited acceptanceAu-Au & p-p spin

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Central Magnet

East Carriage

West Carriage

Ring Imaging CerenkovDrift Chamber

PHENIX Central

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23 USA 11 Japan 6 Korea 5 France 3 China 3 Czech R. 6 Russia 3 Hungary 1 Brazil 2 India 1 Germany 1 Sweden 1 Israel 1 Finland

~ 500 members from 64 institutions:

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West Arm tracking:

DC,PC1, PC2, PC3 electron ID:

RICH, EMCalTOF, Aerogel

photons:EMCal

East Arm tracking:

DC, PC1, TEC, PC3 electron & hadron ID:

RICH,TEC/TRD, TOF, EMC

photons:EMCal

PHENIX Setup as used in 2008

South & North Arm tracking:

MuTr muon ID:

MuID

Other Detectors Vertex & centrality:

ZDC, BBC,RxNP, MPC

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Use transverse energy production: “Highly relativistic nucleus-nucleus collisions: The central rapidity region”,

J.D. Bjorken, Phys. Rev. D27, 140 (1983).

Assumes~ longitudinal expansion ~ boost invariance “central rapidity plateau” Then

0

0 .2

0 .4

0 .6

0 .8

1

1 .2

1 .4

1 .6

-6 -4 -2 0 2 4 6

y

dy

dn

Estimating the Initial Energy Density

2 2 2

1~ ~T T TE dE dE dE

V R dz R dy R dy

Radius of nucleus R~ 6.5 fm

dz dy

Element of longitudinally expanding reaction volume:

2R

is formation time ~ 1fm

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Initial Energy Density at RHIC“Bjorken estimate” relates ET to energy density:

central 2%

PHENIX130 GeV

02j

TB

1 1 d

c dy

E

R

Phys. Rev. Lett. 87, 52301 (2001)

2%

26T39

y 0

dE578 GeV 1.19 0.01

dy

initial energy density (formation time 0=1 fm):

RHIC Au-Au i ~ 4.6 GeV/fm3 15 GeV/fm3

SPS Pb-Pb i ~ 3.0 GeV/fm3

Increase by ~1.15 from 130 GeV to 200 GeV

more realistic formation time ~0.3 fm at RHIC

~30 times normal nuclear density~1.5 to 2 times higher than at SPS (s = 17 GeV)

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one particle ratio (e.g. p/p) determines B/T

a second ratio (e.g. /p) then determines T predict all other hadron abundances and ratios

Thermal yields hadron species abundances in hadrochemical equilibrium

Final State Hadrochemistry

spin isospindegeneracy

temperature atchemical freezeout

baryochemicalpotential

final state: hadron gas close to phase boundary

1

1

2 /3

3

22

Tmp

hhBh

e

pdVgN

lesantipartic and

,.......,,,,,,,,,, DdpKKh

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Kinematic Variables for Particle Production 4-vector of particle

More practical variables:

transverse momentum Lorentz invariant

related transverse mass

Rapidity Lorentz transformation:

related pseudo rapidity

22

cosT

T T

p p

m m p

1ln

2

ln tan2

L

L

E py

E p

p m y

0 90

lab cms beam

ocms cms

y y y

y

mass m (or velocity)momentum p

polar angleazimuth

beam axis

measure:

p and not Lorentz invariant!!

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Basic Cross Sections

Inclusive particle production of particle species a (e.g. ,K,p etc.)

Invariant cross section

Typically measured as yield per event differentially in kinematic variable

And studied as function of centrality

Au Au a X

3 3 2

3 2T T T T

d d dEdp d dy p dp dy p dp

evt

and 1 1

Nevt T T

dN dN

N p dp dy

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Chemical equilibrium may imply kinetic equilibrium first guess: a thermal Boltzmann source:

However, system of interacting particles expands into vacuum System reasonably well described by hydrodynamic evolution Collective behavior, radial and “elliptic” flow Use comparison of hydrodynamic calculation with data to infer input

parameters

3 3 cosh( )

3cosh( ) ~

~

T Tm y mET T T

T TT T

d N d NE Ee m y e m e

dp m dm d dy

Particle Spectra

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mT1/m

T d

N/d

mT

light

heavyT

purely thermalsource

explosivesource

T,

mT1/m

T d

N/d

mT

light

heavy

mT = (pT2 + m2)½

different spectral shapes for particles of different mass strong collective radial flow

reasonable agreement with hydrodynamic prediction at RHIC

Tfo ~ 100 MeV <r> ~ 0.55 c

Full hydro calculation: Initial condition: eq ~ 0.6 fm, Ti ~ 350 MeV, ~ 20 GeV/fm3

RHIC Spectra - an Explosive Source

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translates into momentum anisotropy in final state Fourier expansion

elliptic flow strength

Elliptic Flow → Early Thermalization initial state of non-central Au+Au collision

spatial asymmetry asymmetric pressure gradients

x

zNon-central Collisions

in-plane

out-of-plane

y

Au nucleus

Au nucleus

3 3

R30T T

2 cosnn

d N d NE v n

d p p d dp dy

2 Rcos 2v

shape “washes out” during expansion, i.e. elliptic flow is “self quenching” v2 reflects early interactions and pressure gradients

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Hadron v2 and more Hydrodynamics observations at RHIC

v2 is large and for soft hadrons in reasonable agreement with ideal hydrodynamics (not true at lower energies)

mesons

baryons

Early thermalization in partonic phase

Hadronization (confinement) of constituent quarks!

PHENIX: nucl-ex/0608033

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Key Experimental Probes of Quark Matter

Rutherford experiment atom discovery of nucleus

SLAC electron scattering e proton discovery of quarks

penetrating beam(jets or heavy particles)

absorption or scattering pattern

QGP

Nature provides penetrating beams or “hard probes”and the QGP in A-A collisions

Penetrating beams created by parton scattering before QGP is formed High transverse momentum particles jets Heavy particles open and hidden charm or bottom Calibrated probes calculable in pQCD

Probe QGP created in A-A collisions as transient state after ~ 1 fm

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Hard Probes: Light quark/gluon jets Status

Calibrated probe Strongly modified in opaque medium

Jet quenchingReaction of medium to probe (2 particle corr. Mach cones,

etc)

AAAA

coll pp

YieldR

N Yield

hydrovacuum fragmentationreaction of medium

0-12%

STAR

trigger 2.5-4 GeV, partner 1.0-2.5 GeV

peripheral or pp central AuAu

Matter opaque to color charges Nothing comes out black hole

extreme density e ~ 20 GeV/fm3

Many open questions though!

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I. Transverse Energy

central 2%

PHENIX130 GeV

Bjorken estimate: ~ 0.3 fm

Quark Matter Produced at RHIC

initial ~ 10-20 GeV/fm3

Initial conditions: therm ~ 0.6 -1.0 fm/c

~15-25 GeV/fm3

II. Flow → Hydrodynamics

Heavy ion collisions provide the laboratory to study high T QCD!

III. Jet Quenching

dNg/dy ~ 1100

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Strongly coupled plasma < 1 fm Ti~300 MeV at energy density 5-25 GeV/fm3

“opaque black hole” thermal radiation jet quenching J/ suppression

system evolution expectations/observationscollision hard scattering jets, heavy flavor, photons

confinement at phase boundary TC ~ 170 MeV in chemical equilibrium relative hadron abundance

break down of chiral symmetry modification of meson properties

collective expansion of memory effect in hadron spectra fireball under pressure transverse flow <v/c> ~ 0.5

collective expansion of fireball under pressure

memory effect in hadron spectra elliptic flow

Quark Matter Formation in Heavy Ion Collisions

thermal freeze-out > 10 fm Tf = 100 MeV end of strong interactiontwo and one particle spectra

QGP