Axel Drees, University Stony BrookEINN, Milos Greece, Sep. 23 2005

Energy Loss in Dense Media“Jet Quenching”

PHENIX

PRL 88 (2002) 22301One of the first discoveries at RHIC!

Axel Drees

Outline of My Talk

Introduction Quark Gluon Plasma at RHIC Jets and how they probe the QGP

Jet quenching in heavy ion collisions pp baseline High pt particle suppression in Au-Au d-Au control experiment Suppression of jet-jet correlations

New experimental results Medium modification of jet-correlations Medium modifications of charm spectra

Summary & Outlook

Axel Drees

RHIC Relativistic Heavy Ion Collisions

The Phase Diagram of Nuclear Matter

Color super-conductor

Color-flavorlocking

Critical point

baryon or nucleon density

Tem

per

atur

e

nuclei

Quark-Gluon Plasma

Hadron Gas“frozen Quarks”

Early Universe

Neutron Stars?

QGP in Astrophysics early universe:

time < 106 seconds possibly in the interior

of neutron stars

Quest of heavy ion collisions create QGP as transient

state in heavy ion collisions verify existence of QGP study properties of QGP

170 MeV1Gev/fm3

Overwhelming evidence for strongly interacting plasma produced at RHIC

Axel Drees

I. Transverse Energy

central 2%

PHENIX130 GeV

Bjorken estimate: ~ 0.3 fm

02j

TB

1 1 d

c dy

E

R

Matter at RHIC has 15 GeV/fm3

~15 GeV/fm3

III. Jet Quenching

dNg/dy ~ 1100

Initial conditions: therm ~ 0.6 -1.0 fm/c

~15-25 GeV/fm3

II. HydrodynamicsPHENIXHuovinen et al

V2

Pt GeV/c

Axel Drees

Ideal Experiment to Probe the QGP

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 needs to provide penetrating beams and the QGP in Au-Au collisions

QGP created in Au-Au collisions as transient state for 10 fm penetrating beams created by parton scattering before QGP is formed

high transverse momentum particles jets Heavy particles charm and bottom

Axel Drees

hadrons

leading particle

hadronsleading particle

q

q

hadrons

leadingparticle

leading particle

schematic view of jet production

hadrons

Jets: A Penetrating Probe for Dense Matter

In a gold gold collision Scattered partons travel through dense matter Expected to loose a lot of their energy

Energy loss observed as suppression of high pT leading particles suppression of angular correlation Depending on path length, i.e. centrality and angle to reaction plane

What is a jet? Incoming partons may carry large fraction x of beam

momentum These partons can scatter with large momentum transfer Results in large pT of scattered partons appears in laboratory as “jet” of particles

Jet production can be observed as high pT leading particles angular correlation

reaction plane

Axel Drees

Jet production measured indirectly by transverse momentum (pT) spectrum

Identified particles (0) Charged particles (h = , K, p, .. )

At RHIC energies different mechanisms are responsible for different regions of particle production

Thermally produced “soft” particles “hard” particles from jet production

Hard component can be calculated with QCD

Data agrees with QCD calculation “calibrated” reference

Particle Spectra from p-p Collisions

0 from p-p collisions

soft

hard

( )T

evt T T

dNyield p

N p dp

1

QCD calculation

Axel Drees

Hard-scattering processes in p-p quarks and gluons are point-like objects small probability for scattering in p-p p-p independent superposition of partons

Minimum bias A-A collision assume small medium effects on parton density superposition of independent p,n collisions collision probability increases by A 2

cross section scales by number of binary collisions

Impact parameter selected A-A collisions superposition of p,n collisions among participants calculable analytically by nuclear overlap integral or by MC simulation of geometry “Glauber Model”

Scaling from p-p to Heavy Ion Collisions

hard hard NN hardAA NN NNbinary AA inelN T

Participants

Axel Drees

( )

( )coll

AA T

yield AuAu NR p

yield ppHard processes in Au-Au

scale with Nbinary

Binary Scaling in Au-Au tested with Direct Photons

pp collisions: qg-Compton scattering Direct production described by NLO pQCD

q

qg

Au-Au collisions: Direct rates scale with Nbinary Similar scaling observed for charm quark

production

Axel Drees

Suppression of in Central AuAu Collisions

High pT suppressed by factor ~ 5 pp to central AuAu and peripheral to central Au-Au

PHENIX preliminary

Nuclear modification factor:

PHENIX

PRL 91 (2003) 72301

( )

( )coll

AA T

yield AuAu NR p

yield pp

Axel Drees

Control Experiment with d-Au

Final state effect: no suppressionInitial state effect: suppression

gold-goldcollision

deuteron gold collision

Final state effect “jet quenching” Medium created in d-Au has small volume Jets easily penetrate short distance No suppression of jet yield expected in d-Au

Initial state saturation effect Gluon density saturated in incoming gold nucleus Deuteron shows no or little saturation Expect suppression of jet yield, but with reduced magnitude

.dA AAR R 0 7

dAR 1

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Suppression at Parton Level No suppression for direct photons Hadron suppression persists up to >20 GeV jets Common suppression for 0 and it is at partonic level Typical model calculation: > 15 GeV/fm3; dNg/dy > 1100

Hot opaque partonic medium: > 15 GeV/fm3

Axel Drees

Centrality Dependence of Suppression

Convolute jet absorption or energy loss with nuclear geometry

(many publications)

Centrality dependence characteristic for jet absorption in extremely opaque medium!

Insensitive to details of energy loss mechanism

Hard region: pT > 7 GeV/c Suppression depends on centrality but not on pT Characteristic features of jet fragmentation independent

of centralitypQCD spectral shape h/0 constantxT scaling

Axel Drees

Azimuthal Correlations from Jets

pp jet+jet STAR

Trigger particle with high pT > pT cut 1

to all other particles with pT > pT cut-2

Au+Au ???

0 /2 0

yiel

d/t

rig

ger p+p

yiel

d/t

rig

ger

0 /2 0

Au+Au

random backgroundelliptic flow

0 /2

0

yiel

d/t

rig

ger Au-Au

statistical background subtraction

suppression?

Jet correlations in Au-Au viastatistical background subtraction

Axel Drees

Disappearance of the “Away-Side” Jet

pedestal and flow subtracted

Near-side: p+p, d+Au, Au+Au similarBack-to-back: Au+Au strongly suppressed relative to p+p and d+Au

Suppression of the away side jet in central Au+Au

trigger 6 <pt< 8 GeVpartner 2 < pt < 6 GeV

Integrate yields in some window on near and away side

Axel Drees

Suppression of Back-to-Back Pairs

Away side jets are suppressedconsistent with jet absorption in

opaque medium

Jet correlation strength:

AA

yield(AuAu) backgroundI =

expected

Compared to jet absorption model(J.Jia et al.)

Near side

Away side

“Mono jets” point outward

Axel Drees

Remaining Jets from Matter Surface

8 < pT(trig) < 15 GeV/c

STAR Preliminary

pT(assoc)>6 GeV

D. Magestro, QM2005

Surviving “Di jets”tangential

Qualitatively consistent with

surface emission

Decreased surface/volume

“Mono jets” point outward

~factor 5

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Where Does the Energy Go?

Trigger > 2.5 GeVpartner > 1 GeV

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Modification of Jet Shape at Lower pT

PHENIX preliminary

Near side

Away side

Can jet shape be related toproperties of matter?

Axel Drees

Sound velocity? Dielectric Constant?Jet Tomography will be power tool to probe matter!

Energy loss of jet results in conical shock wave in strongly interacting plasma

Hydrodynamic mach cone? Longitudinal modes ? Cherenkov radiation ?

Momentum conservation “multiple scattering” with meduium

Medium evolution of radiated gluons

Theoretical Speculation:

Wake effect or “sonic boom”

Shuryak et al.

Axel Drees

How opaque is the medium? Check Charm Production!

p+p

Default PYTHIA parameterization PDF – CTEQ5L; mC = 1.25 GeV; mB = 4.1 GeV <kT> = 1.5 GeV; K = 3.5

Parameterization tuned to describe s < 63 GeV p+N world data Spectral shape is “harder” than PYTHIA expectation

pp PHENIX preliminary

background subtracted electron spectrum

Signal:

Background:

D p

e,

p

X

e

e

Axel Drees

Open Charm in Au+Au at sNN=200 GeV

Total yield scales with number of binary collisions

No indication of strong medium modification of

charm production

Axel Drees

Heavy Quark Energy Loss: Nuclear Modification Factor

pp

3

3

AA

AA

3

3

AA

dpσd

T

dpNd

R

Strong modification of the spectral shape

Suppression by factor 2-5, similar to pion suppression

Large bottom contribution above 4 GeV?

Production of charm scales like hard process

Spectral shape modifiedwhile propagating in medium

Axel Drees

Elliptic Flow: A Collective Effect

Initial spatial anisotropy is converted

into momentum anisotropy

x

yz

dn/d ~ 1 + 2 v2(pT) cos (2 ) + ...

Axel Drees

Greco,Ko,Rapp: PLB595(2004)202

Charm Quarks flow with light quarks

Charm flows, strength ~ 60% of light quarks ()

Drop of the flow strength at high pT

due to b-quark contribution? The data favor the model that

charm quark itself flows at low pT.

High parton density and

strong coupling in the matter

Axel Drees

Strongly interacting QGP produced at RHICState of unprecedented energy density ~ 15 GeV/fm3

Opaque to colored “hard” probes, jets and heavy flavor Hard probes will be critical to study properties of QGP

Discovery of jet quenching

On tape; analysis ongoing

Most data seen today

4x larger Au-Au data sample in 2006

Factor 10 luminosity increase with electron coolingafter 2010

Summary & Outlook

2004

20022001

Axel Drees

Backup Slides

Axel Drees

Outlook into the “Away” Future

Quark gluon Compton scattering:

-energy fixes jet energy & Jet direction fix kinematics

measure E as function of: E, “L”, flavor

q

qg

-jet: the golden channel for jet tomography

pQCD direct + jet quenching PHENIX Preliminary

AuAu 200 GeV 0-10%

pQCD direct

70% of photons are prompt photons

Promising measurement at RHIC:every low cross section; pT< 8-10 GeV on tapeluminosity and detector upgrades:

extend range to pT~25 GeV and |y|<3