Particle Production, Correlations, and Jet Quenching at RHIC *

John Harris (Yale University) QCD@Work 2003, Bari, Italy

John HarrisYale University

Particle Production, Correlations, and

Jet Quenching at RHIC*

* Relativistic Heavy Ion Collider


Early Universe

National Geographic(1994)

&Michael Turner

quark-hadronphase transition2 x 1012 Kelvin


“In high-energy physics we have concentrated on experiments in which we distribute a higher and higher amount of energy into a region with smaller and smaller dimensions.

In order to study the question of ‘vacuum’, we must turn to a different direction; we should investigate some ‘bulk’ phenomena by distributing high energy over a relatively large volume.”

T.D. Lee (Nobel Laureate)Rev. Mod. Phys. 47 (1975) 267.


Lattice QCD Calculations

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Purpose of Relativistic Heavy Ion Physics

• Investigate High Density QCD Matter in Laboratory– Determine its properties

• Phase Transitions?– Deconfinement to Quark-Gluon Plasma– Chiral symmetry restoration

• Relevance?– Quark-hadron phase transition in early Universe– Cores of dense stars– High density QCD


Outline

• Introduction• Relativistic Heavy Ion Collider• Particle Production and Correlations• Hard Scattering and Jet Quenching• Conclusions & Future Expectations


Relativistic Heavy Ion Collider

RHIC

STARPHENIX

PHOBOSBRAHMS


Au on Au Event at CM Energy ~ 130 A-GeV

Central Event

color code energy loss

beamview

side view


Space-time Evolution of Collisions

e

space

time jet

Hard Scattering + Thermalization

AuAu

Exp

ansi

on

Hadronization

p K

Freeze-out

QGP

e


Motivation for Particle Production and Correlations at RHIC

• Thermalization?

– Particle yields & ratios, strangeness

chemical equilibration (T, B)

– Spectra

thermal freezeout (Tfo) + collective flow ()

• Pressure gradients particle & energy flow?

– Particle Correlations

transverse (T) & elliptic flow (v2) pressure

• Timescales?

– Bose-Einstein (HBT) Correlations

space-time evolution, system shape and size

• Deconfinement?

– Effects of medium on J/, resonances, parton propagation


Large Number of Produced Particles

dnch/d |=0 = 670

Ntotal ~ 7500

Note - at least 7500 x 2 > 15,000 q + q in final state

(also large number of gluons early)

originally 3 quarks x 2 nuclei x 197 nucleons ~1200 valence quarks

> 92% of (> 15,000) quarks in final state are produced

dN

ch/d

M. Baker (PHOBOS) QM2002

= - ln [ tan(/2)]

Au + Auat RHIC


Boost-Invariance at Mid-rapidityd

Nch

/d M. Baker (PHOBOS) QM2002

Longitudinal Flow (Bjorken expansion)Boost invariant - central rapidity plateau

1ηcosh/m)(p

/m)coshη(pη),(p

η

y :Jacobian

22

STAR


Energy Densities at RHIC

1

11

02

02 dy

dNm

Rdy

dE

R

TT

Bj Longitudinal expansion –

J.D. Bjorken, PRD27 (1983) 140.

R2

dydz 0

for Au+Au: R = 6.5 fm, R2 ~ 130 fm2

dET/d ~ 600 GeV <mT> dN/dy = 0.534 GeV (1150)

dET/d GeV/fm3 –dn/d GeV/fm3

PHENIX

30 x nuclear density > 4 x c

R2

dydz 0


General Particle Ratios Chemical Equilibrium

Statistical Model fits particle ratios for 200 GeV Au + Au:

T = 177 MeV B = 29 MeV

John Harris QCD@Work 2003, Bari, Italy

Elliptic Flow – a Probe of Early Dynamics

XZ-plane - the reaction plane

Transverse Plane

22

22

xy

xy

XY

Azimuthal anisotropy elliptic flow measures response of the system to early pressure the system’s ability to convert original spatial anisotropy into momentum anisotropy

• sensitive to early dynamics of initial system

2cos2 vx

y

p

patan

v2: 2nd Fourier harmonic coefficient of azimuthal distribution of particles with respect to the reaction plane measures elliptic flow 2cos2 v


Hydrodynamic Calculation of Elliptic Flow

P. Kolb, J. Sollfrank, and U. Heinz

Contours of equal energy density

Au+Au at b=7 fm

= 3.2 fm/c = 8 fm/c

y (f

m)

x (fm)


Charged Particle Elliptic Flow (v2)

STAR PRL87 (2001)182301

STAR

Evidence that initial spatial asymmetry is efficiently translated into momentum space anisotropy (as in hydrodynamics)Increasing pressure gradients in the system

RG + QGPResonancegas

Mass dependence of V2(pT) sensitive probe of QCD EOS P (T)Rapid pressure buildup, explosive hydrodynamic expansionHydrodynamics needs quark-gluon softening of the hadronic EOS P. Huovinen, P. Kolb, U. Heinz & indepedently D. Teaney et al. also CM Ko et al., M. Bleicher et al., J. Kapusta et al.


Characteristics of RHIC Collisions from Experiment

Summary of Soft Physics

from the > 40 refereed journal publications from RHIC experiments:

global observations:

Large produced particle multiplicities dnch/d |=0 = 670, Ntotal ~ 7500

92% of (>15,000) quarks of final state are produced quarks

Large energy densities dn/ddET/d GeV/fm3 –Large elliptic flow Large early pressure gradients and gluon densities

“chemical” equilibration:

Small net baryon density K+/K-,B/B ratios) B ~ 25 - 40 MeV

Quark coalescence B/B ratios)

Chemical Freezeout T from global particle ratios) T = 177 MeV, B = 29 MeV

“thermal” equilibration :

Thermal freezeout + large transverse flowTFO = 100-110 MeV, T = 0.5 – 0.6c

expansion dynamics:

No long-lived mixed phase (from Bose-Einstein correlations)

Short chemical-to-thermal freeze-out interval (particle spectra, resonances and particle yields, multi-strange baryons spectra, HBT correlations)


From the Quark-Gluon Quagmire Emerges Hard Scattering

hadrons

leading particle

hadrons

leading particle

New for heavy ion physics Hard Parton Scattering sNN = 200 GeV at RHIC (vs 17 GeV at SPS)

Jets and mini-jets 30 - 50 % of particle production

high pt leading particles (jets?) azimuthal correlations

Scattered partons propagateradiate energy (~ few GeV/fm) in colored medium

suppression of high pt particles

alter di-jets and azimuthal correlations


Hadron Spectra: Comparison of AA to NN

Nuclear Modification Factor RAA:AA = Nucleus-NucleusNN = Nucleon-Nucleon

ddpdT

ddpNdpR

TNN

AA

TAA

TAA /

/)(

2

2

Nuclear overlap integral:# binary NN collisions / inelastic NN cross section

NN cross section

AA cross section

AA

(pQCD)

Suppression:Parton energy loss R < 1 at large Pt


Comparison: pA and Pb+Pb to p+p at Lower s

SPS: If any parton energy loss, it is overwhelmed by initial state soft multiple scattering(Cronin effect)

Transverse Momentum (GeV/c)

RAA

CERN SPS Ions – central collisions tppA ppA FNAL fixed target

Initial state soft multiple scattering (Cronin effect)

R = 1QCD

R > 1nuclear effects(Cronin)

RHIC: RAA < 1 for central Au+Au

K. Adcox et al. , Phys. Rev. Lett. 88, 022301 (2002)

C. Adler et al. , Phys. Rev. Lett. 89, 202301 (2002)

rati

o o

f c

entr

al A

A /s

cale

dp

pSuppression of Hadron Production Observed at RHIC


Inclusive Hadron pt-spectra: s = 200 GeV AuAu

200 GeV results from all experiments

nucl-ex/0302015Submitted to Phys Lett B

nucl-ex/0305015 STAR PRL 89, 202301

Au-Au nucl-ex/0304022p+phep-ex/0304038

PHENIX


Centrality dependence of RAA in Au+Au at s = 200 GeV

nucl-ex/0304022

nucl-ex/0305015

h+/-STAR

Au-Au nucl-ex/0304022


Centrality dependence of RAA in Au+Au at s = 200 GeV

nucl-ex/0305015

h+/-STAR


Particle Species Dependence of RCP (central/peripheral)in Au+Au at s = 200 GeV

• 1.5<pT<3.5 GeV/c: baryons not suppressed p, scales ~ Nbinary

0, K

0

s suppressed

• by pT ~ 6 GeV/c: , K0s, charged hadrons scale similarly

• explanations?

Partonic flow? Quark recombination? Modified fragmentation? Cronin effect?

preliminaryAu+Au

STAR

John Harris (Yale University) PANIC02, Osaka, Japan

Jets at RHIC?

Jet event in eecollision STAR p + p jet event

Can we see jets in high energy Au+Au?

STAR Au+Au (jet?) event


Hard Scattering: Two-Particle Azimuthal Correlations

Technique:

Azimuthal correlation function

Trigger particle

pT > 4 GeV/c

Associate tracks

2 < pT < pT(trigger)

STAR

C2 () 1

N trigger

1

efficiencyd()N ( ,)

di-jets from p + p at 200 GeV


Using p+p Di-jets to Study Central Au+Au Jets -Away-side Jet Disappears

Assume:high pT triggered Au+Au event

is a superposition:high pT triggered p+p event +

elliptic flow of AuAu event

C2(Au Au) C2(p p) A*(1 2v22 cos(2))

– v2 from reaction plane analysis

– A from fit in non-jet region (0.75 < || < 2.24)

Peripheral Au + Au

Away-side jet

Central Au + Au

disappears


High Pt Particle Suppression Jet Suppression

STAR Preliminary

Hadron suppression disappearance of back-to-back ‘jet’!

STAR PRL 90, 082302


Experiment Confronts Theory

STAR nucl-ex/0305015 pQCD-I: Wang, nucl-th/0305010pQCD-II: Vitev and Gyulassy, PRL 89, 252301Saturation: KLM, Phys Lett B561, 93

pT > 5 GeV/c data described by saturation model (up to 60% central) and pQCD + jet quenching


Disentangling Initial and Final State Effects at RHIC!

RAA d 2N AA dydpT

d 2N pp dydpT NcollAA

I. Vitev & M. Gyulassy, Phys.Rev.Lett. 89 (2002) pQCD + jet-quenching

Effect of “Cronin” and nuclear shadowing

Measure d+Au (for initial state effects) compare to p+p and Au+Au

+ quenching

SPS: Cronin dominantRHIC: Cronin, shadow, quench (dNg/dy)

RAA “flat”


No Suppression Observed in d + Au at RHIC!

PHOBOS Preliminary h±

h±

o

PHENIX Preliminary

STAR

Preliminary h±


No Suppression Observed in d + Au at RHIC!

STAR

Preliminary h±


Comparing p + p, d + Au and Au + Au Jets

d + Au di-jets ~ p + p di-jetsvs

disappearance of central Au + Au away-side jet

STAR preliminary


High Pt Summary

Hadron spectra (vs binary scaling) High Pt hadrons suppressed in central Au + Au enhanced in d + AuBack-to-back Jets Di-jets in p + p, d + Au

(all centralities) Away-side jets quenched

in central Au + Au emission from surface

x


Future at RHIC – Hard Probes

RAA d 2N AA dydpT


Charmonium (cc suppression/enhancement)- PHENIX start

Open Charm (charm production rates) – PHENIX recent PRLPHENIX - K. Adcox et al., Phys. Rev. Lett. 88, 192303 (2002)

Higher Pt triggers, jets fix parton energy loss (theory…)

Quantitative answers to questions on properties

Polarized pp measurements up to s = 500 GeV

(gluon and sea-quark contribution to proton spin)

Direct Photon Radiation?

New phenomena…….


Thanks


RAA d 2N AA dydpT


STAR, PHENIX, BRAHMS, PHOBOS CollaborationsRHIC Operations Group

for contributions and/or discussions:W. BuszaA. DreesM. GyulassyD. HardtkeP. JacobsM. MillerT. UllrichF. VidebaekX.N. WangW. Zajc

And all others I forgot to mention



RAA d 2N AA dydpT


End of Presentation

Extra Slides Follow


• How can we determine the parton’s energy loss?

Energy Loss of Scattered Partons in Dense Matter

• elastic scattering of partons dE/dx ~ 0.1 GeV/fm Bjorken (1983)

• nonlinear interaction of gluons dE/dx ~ few GeV/fm Baier et al (1998)

gluesR

BDMS vLC

E ~4

22

• nonlinear interaction of gluons in thin plasma Gyulassy et al (2001)

L

ELogrdCE jet

glueSRGLV 23 2

,

Linear dep. on gluon density


Do We Know the Energy Loss in Confined Matter?Wang and Wang, hep-ph/0202105

Modification of fragmentation in e-Nucleus scattering:

10 GeV quark: dE/dx ~ 0.5 GeV/fm

F. Arleo, hep-ph/0201066

x1

Drell-Yan production in -Nucleus:

50 GeV quark: dE/dx <0.2 GeV/fm


Suppression at RHIC: Data Confronts Theory

Properties of the Medium

Parton Energy Loss : dE/dx ≈ 0.25 GeV/fm (expanding)

dE/dx|eff

≈ 7 GeV/fm (static source)

~ 15 times that in cold Au nuclei

Opacities: <n> = L/≈ 3 – 4

Gluon densities: dNg/dy ~ 900


“High” Pt Summary - Exp vs Theory

Ivan Vitev, QM2002

Preliminary sNN = 200 GeV

Wang and Wang, hep-ph/0202105Observe: strong suppression of high Pt hadrons

Requires: dE/dx = 7.3 GeV/fm ~ 10-15 times cold matter

gluon densities dngluon/dy ~ 500 – 1000

Suppression: an initial state effect?

Gluon Saturation (color glass condensate)

Wavefunction of low x gluons overlap; the self-coupling gluons fuse, saturating the density of

gluons in the initial state. (gets Nch right!)

• Multiple elastic scatterings (Cronin effect) Wang, Kopeliovich, Levai, Accardi

• Nuclear shadowing

Gribov, Levin, Ryshkin, Mueller, Qiu, Kharzeev, McLerran, Venugopalan,

Balitsky, Kovchegov, Kovner, Iancu …

probe rest frame

r/ggg

dAu AuAuR R RdAu~ 0.5D.Kharzeev et al., hep-ph/0210033

1dAuR

decreases dAuR

Broaden pT :

Particle Production, Correlations, and Jet Quenching at RHIC *

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