Bulk properties of QCD from the hard sector at RHIC

Institut de Physique – Université de Liège

Liège, Belgique, Feb. 25, 2004

David d’Enterria

Nevis Labs, Columbia University, NY

Overview

1. Introduction:

The goal: study Quantum Chromo many-body Dynamics: QGP, CGC.

The means: compare hard scattering production in diff. colliding systems.

2. “QCD vacuum” production – high pT spectra in p+p:

Baseline reference data of hard scattering in free space.

3. “Hot QCD medium” production – high pT spectra in central A+A:

Light-flavour (u,d,s): Suppressed (compared to free space).

ronic (g): Unsuppressed.

4. “Cold QCD medium” production – high pT spectra in d+Au:

 Light-flavour (u,d,s) production: Enhanced at y ≤ 0 (mid&forward)

Suppressed at y ≥ 1 (backwards

5. What have we learnt ? Data vs. theory.

6. Summary

Suppressed hadron production (compared to free space):

s, pT, y, centrality, and particle species dependence.

 Enhanced hadron production at y ≤ 0 (mid-rapidity & high x2 in Au):

pT, centrality, and particle species dependence.

 Suppressed at y ≥ 1 (small x2 in Au).

CGC ?

QGP ?

}

Review of QCD properties

The QCD Lagrangian:

- Degrees of freedom: quarks and gluons

- Non-abelian gauge theory

- Internal symmetry group: SU(3)color

Properties of the strong interaction:

1. Confinement: Quarks do not occur isolated in nature: only in hadronic (colorless) bound-states as mesons [qq] & baryons [qqq]. as(Q2) strong at large distances (low Q2).

2. Asymptotic freedom: At short distances (high Q2), as(Q2) decreases logarithmically: quarks & gluons weakly coupled. Perturbative methods applicable (pQCD).

3. Chiral symmetry breaking:

Quarks acquire dynamically a mass in a confined medium:

Current mq (5-10 MeV) << Constituent mq (~300 MeV)

Non-zero QCD ground-state (non-perturbative vacuum, "sea") filled with quark-antiquark and gluon-gluon virtual pairs :

quark & gluon condensates: <YY>»-(235 MeV)3, <asGmnGmn>»-(500 MeV)4

_

_

as(Q2) ~1/ln(Q2/L2), L~200 MeV

(as=g2/4p)

QCD at finite T and 

New state of matter

QCD color

potential:

QCD

vacuum:

Quark

masses:

u/d quarks:

s quark :

mq~m0+C<YY>

(NJL model)

_

}

V = s r

(multi-gluon

exchange)

Bag

pressure:

B1/4 ~ 0.2 GeV

“empty” vacuum

q&g can roam freely

over large volume

“true” non-perturbative vacuum

perturbative vacuum

V ~ s r [1-exp(-m r) /m r] , m = rD-1

Yukawa-like potential:

V ~ -aeff / r

(1-gluon

exchange)

String tension

s ~ 1GeV/fm

Debye Screening

High T & r

T= 0

High T

Nuclear matter at high temperatures and densities exhibits:

Color deconfinement: aeff (T) ~1/ln(T,r) ®0

Chiral symmetry restoration: mq(T,r) ® 0

QGP

(*) At zero baryon number density (B=0)

QCD thermodynamics on the lattice (*)

QCD critical temperature:

Tc = (173 ±10) MeV [nf =2]

Tc = (154 ±10) MeV [nf =3]

Critical energy density:

ec=(6 ± 2)Tc4 Þ ec=(0.7±0.3) GeV/fm3

HG

QGP

Phases of strongly interacting matter

color super

conductor



Hadron

gas

HG

QCD Equation of State

Pressure

Energy density

Insights into the cosmology and phase transitions of the early universe

Time duration of the

phase transition: O (ms)

Cosmological QCD transition

The universe was in the QGP state ~10 μs after the “Big Bang”

log (time)

Small-x and saturation physics

Initial conditions at RHIC: high-energies + large nuclei

Values of small-x: xBj= 2pT/√s <<1

Large gluon densities

Colliding nuclei described

via a colored highly saturated

gluonic wave-function

(“Color Glass Condensate”):

RHIC ~ HERA x A1/ 3

Study regime of non-linear (high density)

many-body parton dynamics @ small-x (CGC).

The "Little Bang" in the lab.

High-energy nucleus-nucleus collisions: in fixed-target reactions (s~17 GeV, SPS) or at colliders (s~200 GeV, RHIC)

QGP expected to be formed in a tiny region (~10-14 m) and to last very short times (~10-23 s).

Collision dynamics: Diff. observables probe diff. reaction stages

Time

Penetrating

probes

t~0.1 fm/c

t ~ 10 fm/c

t ~ 107 fm/c

Penetrating probes

Final state probes

Hard QCD probes. Motivation (I)

Hard probes: High-pT, jets, direct , heavy-quarks (D, B), ...

[1] Early production ( ~ 1/pT< 0.1 fm/c) in parton-parton scatterings with large Q2:

Closest experimental probes to underlying QCD (q,g) degrees of freedom.

[2] Direct probes of partonic phase(s)  Sensitive to QCD medium properties:

[3] Incoherent processes: Direct comparison A+A to p+p yields via “ Ncoll scaling” :

dAB → hard = A·B·dpp → hard

At impact parameter b: dAB(hard) = TAB(b) dpp(hard)

Nuclear overlap:TAB (b)  Ncoll(b) : number of inel. NN collisions.

q: fast color triplet

g: fast color octet

Q: slow color triplet

QQbar: slow color

singlet/octet

Virtual photon: colorless

Real photon: colorless

Unknown QCD Medium

Induced

gluon

radiation ?

Energy

Loss ?

Dissociation ?

Controls

QCD probe in

QCD medium

(possible quark-gluon plasma?)

Modification?

QCD probe out

Hard QCD probes. Motivation (I)

[4] Production yields theoretically calculable via:

perturbative-QCD or ...	classical-field QCD:

A

B

A

B

at small-x ...

Mueller diagram for

classical glue radiation

Hard scattering in A+A collisions

Hard scattering in A+A collisions

Leading-twist shadowing

or

Gluon saturation (CGC)

pT broadening

(Cronin enhancement)

[Experimental handle: p,d+A]

[Experiment. handle: e+A, p,d+A]

Initial-state effects

Hard scattering in A+A collisions

Leading-twist shadowing

or

Gluon saturation (CGC)

pT broadening

(Cronin enhancement)

medium-induced

parton energy loss:

“jet quenching” in QGP

possible hadronic

rescattering

[Experimental handle: p,d+A]

[Experiment. handle: e+A, p,d+A]

[Experimental handle: A+A]

Initial-state effects

Final-state effects

Hard scattering in A+A collisions

Leading-twist shadowing

or

Gluon saturation (CGC)

pT broadening

(Cronin enhancement)

medium-induced

parton energy loss:

“jet quenching” in QGP

possible hadronic

rescattering

Approach: Study modifs. (incl. spectra, partic. composition) of high pT production in A+A with respect to p+p, p+A to learn about QCD many-body dynamics:

“Quark Gluon Plasma” (final-state A+A) and/or

“Color Glass Condensate" (initial-state A).

Initial-state effects:	Final-state effects

[Experimental handle: p,d+A]

[Experiment. handle: e+A, p,d+A]

[Experimental handle: A+A]

Hard scatt. in A+A (large soft backgd) studied via high pT (leading) hadron = jet tag.

Initial-state effects

Final-state effects

Final-state QGP effects

Multiple final-state gluon radiation off the produced

hard parton induced by the traversed dense

colored medium:

Mean parton energy loss probes medium

properties:

DEloss ~ gluon (gluon density)

DEloss ~ DL2 (medium length)

Energy is carried away by gluonstrahlung

outside jet cone: dE/dx ~ s k2T

Formalisms: BDMPS (thick plasma), GLV (thin plasma),

Correction for expanding plasma (1-D):

E1-D =(20/RA) · Estatic ~ 15·Estatic (0=0.2 fm/c, RA=6 fm)

Expected result: Suppression of high pT leading hadrons due to non-abelian final-state gluon radiation.

g

Jet

High- pT hadron

Gluon

bremsstrahlung

QGP

~ 1.5 GeV2/c2 @ RHIC

Initial-state CGC effects

Nucleus-nucleus collisions described as a

collision of two “classical” gluonic wave-functions

(“Color Glass Condensate”).

Approximation valid around “saturation scale”:

Q2s >> L2QCD  as<<1 (weak coupling)

"Classical" (Chromo-Dynamics) methods applicable

Particle production via glue-glue collisions:

Extension to pT > Qs (“geometric scaling”)

via quantum evolution.

Expected result: gluon fusion at low x leads to an effective depletion of the number of partonic scattering centers in the initial state.

Relativistic Heavy-Ion Collider (RHIC) @ BNL

STAR

PHOBOS

PHENIX

Specifications:

3.83 km circumference

2 independent rings:

120 bunches/ring

106 ns crossing time

A + A collisions @ √s = 200 GeV

Luminosity: 2·1026 cm-2 s-1 (~1.4 kHz)

p+p collisions @ 500 GeV

p+A collisions @ 200 GeV

4 experiments:

BRAHMS, PHENIX, PHOBOS, STAR

Run-1 (2000): Au+Au @ 130 GeV

Run-2 (2001-2): Au+Au, p+p @ 200 GeV

Run-3 (2002-3): d+Au, p+p @ 200 GeV

Run-4 (2004): Au+Au, p+p @ 200 GeV

BRAHMS

The PHENIX collaboration

11 countries

51 institutions

400+ collaborators

Pioneering High-Energy Ion eXperiment

PHENIX @ RHIC

11 detector sub-systems

2 Arm central spectrometers:

|h|< 0.35, Df = p (e, g, hadrons)

Open geometry axial field

2 forward spectrometers:

1.2 < |h|< 2.5, Df = 2p (muons)

Radial magnetic field

3 global (inner) dets.: trigger, centrality

Designed to measure rare probes:

+ high rate capability & granularity

+ good mass resolution and PID

- limited acceptance

PHENIX run history

2000

2001/2002

2002/2003

Run Year Species s1/2 [GeV ]  Ldt Ntot tot. data

01 2000 Au - Au 130 1 μb-1 10M 3 TB

02 2001/2002 Au - Au 200 24 μb-1 170M ~20 TB

p- p 200 0.15 pb-1 3.7G ~10 TB

03 2002/2003 d - Au 200 2.74 nb-1 5.5 G 46 TB

p - p 200 0.35 pb-1 4.0G 35 TB

Au+Au @ 200 GeV in PHENIX

~ 600 charged particles per unit rapidity at midrapidity (top 10% central)

Foreword: central rapidity densities in Au+Au

dNch/dy constraints mechanisms of initial multi-particle production:

dNch/dy (per participant pair) increases faster than linearly with Npart :

Particle density at y=0 well described by pQCD- & CGC- based models alike:

 "Soft + hard" (string + pQCD “minijet”): increased hard contribution (Ncoll )

 Initial-state gluon saturation (CGC): dNch/dy ~ dNgluon/dy ~ 1/as ~ Npartln(Npart )

Au+Au 200 GeV

PHENIX

N.Armesto et al.

Int.J.Mod.Phys. A15, 2019

dNch/dy

centrality dependence:

Au+Au: high pT spectra

PRL 88, 022301(2002)

π0

PRL 88, 242301 (2002)

PRL 91, 172301 (2003)

nucl-ex/0304022

Neutral pions up to pT~10 GeV/c in 9 centrality bins

p,pbar up to

pT~4.5 GeV/c in

5 centrality bins

PRL 91, 241803

nucl-ex/0304022

π0

PLB 561, 82 (2003)

PHENIX

PRC to appear

(h++h-)/2

Au+Au: latest p0 high pT spectra ...

large amount of

high quality high pT data

10 centralities

8 orders of magnitude

pTmax = 15 GeV/c

High pT p+p @ 200 GeV: “baseline” data

p+p  p0 X	p+p  h± X (Non Singly Diffractive)

Good theoretical (NLO pQCD) description

STAR Collab.

PRL91, 172302

nucl-ex/0305015

KKP FF

Kretzer FF

(PDF: CTEQ6M)

PHENIX Collab.

PRL91, 241803

hep-ex/0304038

Well calibrated (experimentally &

theoretically) p+p references at hand !

Parenthesis (1): p+p physics @ high pT

p+p di-X	p+p,pbar  h± X (Singly Diffractive)

Intrinsic <kT> = 725 ± 34 MeV/c

Jet characterization (kT,jT ...)

STAR

UA1

UA5

Adapted from K.Goulianos

hep-ph/0308183

J. Rak (PHENIX Coll.)

hep-ph/0306031

Dihadron

(PHENIX preliminary)

sSD(STAR) ~ 9 ± 3.5 mb

sSD(UA1) = 7 ± 1 mb

sSD(UA5) = 4.8 ± 0.9 mb

Diffractive physics

Au+Au vs. p+p @ 200 GeV (p0)

Au+Au p0 X (peripheral) Au+Au p0 X (central)

Peripheral data agree well with Strong suppression in

p+p (data&pQCD) plus Ncoll scaling central Au+Au collisions

D.d'E. nucl-ex/0309015

Nuclear modification factor (p0)

Discovery of

high pT suppression

(one of most significant

results @ RHIC so far)

PHENIX Collab.

PRL 91, 072303 (2003)

nucl-ex/0304022

Ncoll scaling

(“hard” production)

x4-5 suppression

Npart scaling

(“soft” production)

Nuclear modification factor: √sNN dependence

A.L.S.Angelis, PLB 185, 213 (1987)

WA98, EPJ C 23, 225 (2002)

PHENIX, PRL 88 022301 (2002)

PHENIX, PRL 91, 072303 (2003)

CERN: Pb+Pb (√sNN = 17.3 GeV), a+a (√sNN = 31 GeV): Cronin enhancement.

RHIC: Au+Au (√sNN = 130, 200 GeV): x 4-5 suppression.

Ncoll scaling

(“hard” production)

Npart scaling

(“soft” production)

RAA ~ 0.4

RAA (p0) compilation in nucleus-nucleus collisions:

RAA ~ 2.0

RAA ~ 1.5

RAA~0.2

High pT suppression: centrality dependence (I)

peripheral	central

Smooth evolution of suppression w.r.t. Ncoll scaling

(in agreement with pQCD+parton energy loss expectations):

pQCD+partonic ΔEloss

(1+1D expansion)

PHENIX Collab.

to appear in PRC

nucl-ex/0308006

X.N.Wang,

nucl-th/0307036

back to RHIC energies ....

pQCD expectation

(w/o energy loss)

CGC prediction

RAANpart

Npart

High pT suppression: centrality dependence (II)

Let's change the A+A/p+p scaling factor now: Ncoll(hard) Npart(soft)

Approx. Npart scaling: high pT production per participant pair ~const. in wide range of centralities

In accord with Color Glass Condensate predictions too

D.Kharzeev, E.Levin, L.McLerran

PLB 561, 93 (2003)

PHENIX Collab.

to appear in PRC

nucl-ex/0308006

High pT suppression. Particle dependence (I): h± vs. π0

Inclusive charged hadrons suppressed a factor ~ 4 – 5 at pT> 5 GeV/c

... but less suppressed than π0 within pT = 2 – 5 GeV/c.

Universal (PID-wise) suppression above pT = 5 GeV/c

~15% overall normalization

errors not included

High pT suppression - Particle depend. (II): baryons vs. mesons

Rc p (ratio central/peripheral) at intermediate pT = 2 – 4 GeV/c:

1. Baryons: p, p, Λ, Λ NOT suppressed in central Au+Au.

2. Mesons: p0, k0s, η equally suppressed.

Particle composition inconsistent with known fragmentation functions.

Different production mechanism for baryons and mesons in the intermediate pT range (recombination vs. fragmentation ?).

STAR Collab.

subm. to PRL,

nucl-ex/0306007

PHENIX Collab.

PRL91:172301(2003)

_ _

High pT suppression - Particle dependence (III): p/π, h±/π

Central colls.: p/π ~ 0.8 (at pT = 2 - 4 GeV/c) at variance with perturbative production mechanisms (favour lightest meson).

Periph. colls.: p/π ~ 0.2 as in p+p,p (ISR,FNAL) & in e+e- jet fragmentation

Baryon enhancement limited to pT < 4.5 GeV/c: Charged hadron (h± = π± + p(pbar) + K± ) and π0 equally suppressed above pT ~ 5 GeV/c:

h / π ~ 1.6 as in p+p (perturbative ratio)

PHENIX Collab.

PRL91:172301(2003)

nucl-ex/0305036

High pT in d+Au (“control” experiment)

hot & dense medium	cold medium

(initial+final-state effects)	(initial- state effects only)

A+Au collision

p,d+Au collision

d+Au nuclear modification factor (at y=0)

d+Au @ √sNN = 200 GeV	p+A @ √sNN = 20 - 40 GeV

High pT d+Au unquenched ! RdAu > 1.

Reminiscent of p+A “Cronin enhancement” (initial-state soft & semihard scattering).

No Au gluon saturation effects in kinematic region probed (y = 0).

d+Au nuclear modification factor

RAA vs. RdA (y = 0) : centrality dependence

PERIPHERAL Au+Au & d+Au

preliminary

RAA vs. RdA (y = 0) : centrality dependence

MID-PERIPHERAL Au+Au & d+Au

preliminary

RAA vs. RdA (y = 0) : centrality dependence

MID-CENTRAL Au+Au & d+Au

preliminary

RAA vs. RdA (y = 0) : centrality dependence

CENTRAL Au+Au & d+Au

preliminary

RAA vs. RdA (y = 0) : centrality dependence

Opposite centrality dependence of d+Au nuclear enhancement compared to Au+Au nuclear suppression.

(Model-independent) conclusion: Au+Au suppression at y = 0 not due to a “cold” (initial-state) nuclear matter effect: gluon saturation effects not relevant, final-state (QGP) interpretation favoured.

preliminary

The quest for gluon saturation effects @ RHIC ...

RHIC kinematical regime:

High pT @ midrapidity:

y = 0, Q2 = 1-100 GeV2/c2

- pQCD collinear factorization

- DGLAP evolution (g splitting)

- small (~20%) nuclear effects

in PDFs (LT shadowing).

Moderate pT, rapidities:

y ≈ 1-3, Q2 ≈ 10 GeV2/c2

- kT factorization

- linear BFKL evolution (g splitt.)

- “moderate” nuclear effects.

Low pT @ large rapidities:

y > 3, Q2 < Qs2 ≈ 5 GeV2/c2

- pQCD factorization breakdown

- non-linear evolution (g fusion)

- strong nuclear effects in the

initial-state

xT = pT /√s (e-y+ey)

(2 → 2)

d+Au nuclear modification factor (η = 3.2)

Significant suppression (factor ~2-3) of moderately high pT hadro- production at η = 3.2 (small x2 in Au).

First time a large suppression is seen at small-x and high pT

Qualitative agreement with gluon saturation / strong shadowing effects.

BRAHMS preliminary

η = 0. (x ≈ 10-2)

η = 3.2 (x ≈ 5∙10-4)

xT = pT /√s (e-y+ey)

for pT=2 GeV/c:

why the excitement in some circles...

Take the predictions of a standard “leading twist” approach ...

NLO DGLAP global analysis of nuclear PDFs (fit to ~450 experimental points from e,μ+A, p+A Drell-Yann data):

Maximum gluon shadowing at x~10-4 (indirectly) constrained by all available DIS data on nuclear targets is ~0.8

IF indeed RG(x=10-4) ≈ 0.4 (as suggested by BRAHMS), this could be an evidence of breakdown of QCD factorization at high pT (due to high twist effects at small-x).

D. de Florian & R.Sassot

hep-ph/0311227

Q2=10 GeV2

RG(x)

but (1) ... soft production is also suppressed in d+Au

Particle multiplicities (low pT) in d+Au well below expectations from Npart tot scaling compared to p+p at forward rapidities (d fragmentation) !

Well known from p+A at lower sqrt(s). How this affect high pT production?

Bottom line: Be careful with blind application of “usual” scaling laws for particle production at forward rapidities in asymmetric systems !

p+p

d+Au

but (2) ... valence q (not g) dominate BRAHMS data

h+ > h- : deuteron valence quarks (high x1) dominate over “wee” gluons from Au (small x2).

(Personal) Conclusion: It's premature to claim RGluon(x=10-4) ≈ 0.4

It's premature to claim CGC effects at RHIC.

BRAHMS preliminary

What hard scattering data at RHIC
tell us(*) about the properties of the
underlying QCD matter ...

Summary of possible physical scenarios:

1. Dense final-state partonic medium: Parton energy loss +

quark recombination.

2. Dense initial-state partonic medium: Gluon saturation.

3. Dense final-state hadronic medium: hadronic energy loss.

(*) via confronting data to theory

Final-state “QGP” effects vs. data (I)

Dense medium properties according to “jet quenching” models:

Initial gluon densities:

dNg/dy ~ 1100 [Vitev & Gyulassy]

Opacities:

<n> = L/≈ 3 – 4 [Levai et al.]

Transport coefficients:

<q 0> ~ 3.5 GeV/fm2 [BDMPS, F.Arleo ]

Plasma temperatures:

T ~ 0.4 GeV [G. Moore]

Medium-induced radiative

energy losses:

dE/dx ≈ 0.25 GeV/fm (expanding)

dE/dx|eff ≈ 14 GeV/fm (static source) [X.N.Wang]

Large opacities imply fast thermalization.

All these values imply energy densities well above εcrit QCD in thermalized syst.

Final-state “QGP” effects vs. data (II)

Hwa & Yang

PRC 67, 034902

Greco, Ko, Levai

PRL 90, 202302

Fries, Mueller, Nonaka, Bass

PRL 90, 202303

Quark recombination (coalescence) mechanisms provide a simple explanation of anomalous chemistry at intermediate pT's (2-5 GeV/c):

By quark momenta addition, recombination

dominates for pT ~ 1- 4 GeV/c:

pT(baryons)> pT(mesons)> pT(quarks)

Fragmentation dominates for pT > 5 GeV/c:

pT(hadrons)= z pT(partons) , with z<1

High parton densities in a thermal medium

are required.

However... is recomb. consistent with

(p+p-like) Au+Au dN/dφ near-side widths ?

Final-state effects in a dense hadronic medium ?

Energy loss of “pre-hadrons” inside a dense expanding hadronic fireball.

Nuclear modification factor for a expanding system with εinit≈1 GeV/fm3

State-of-the-art hadronic models (HSD, UrQMD) produce suppression but not enough to explain the observed suppression factor at high pT

Cassing, Gallmeister, Bratkovskaya,

Greiner, Stoecker, nucl-th/0312049

Summary

 High pT central Au+Au vs p+p at midrapidity at RHIC:

 Observation 1: Light-flavor (u,d,s) spectra suppressed by a factor 4-5.

(possible suppression already at √s ≈ 20 GeV).

 Observation 2: Intermediate pT light-flavor composition inconsistent	with known fragmentation functions in free space.

 High pT d+Au vs p+p at midrapidity at RHIC:

 Observation 5: Spectra enhanced by a factor ~1.3

 “Explanation” (1,2 via 4,5): pQCD hard scattering + final-state parton	energy loss + parton recombination:

 Dense thermal QCD medium.

 QGP ? (Run-4 @ RHIC): thermal γ from plasma ?, J/Ψ suppression ?

 High pT in d+Au at forward rapidities at RHIC:

 Observation 6: Spectra suppressed by a factor ~2.

 “Explanation” (6): possible evidence of high twist effects at small-x.

backup slides ...

High pT @ CERN-SPS: “Cronin” or “quenching” ?

New nuclear modification factor (better p+p → π0 ref. @ √sNN = 17.3 GeV)

[D.d'E. to be submitted]

No “Cronin” effect in central collisions (RAA ~ 1).

“Cronin” enhancement in peripheral ... and suppression in top central ?

Look for onset of suppression at RHIC Au+Au, p+p @ √sNN≈ 20 GeV ?

0-8% central

Peripheral

1% top central

High pT azimuthal correlations: Elliptic flow (I)

Elliptic flow = v2 second Fourier coefficient

Large v2 signal (saturating @ high pT):

Exhausting hydro limit for pT<1.5 GeV/c

 Strong (collective) pressure grads.

 Large and fast (t<1.0 fm/c) parton	rescattering: early thermalization.

Initial anisotropy in coord. space (overlap) in non-central collisions translates into final azimuthal asymmetry in momemtum space (transverse to react. plane)

1. Truly collective effect (absent in p+p colls.).

2. “Hard” probe: develops exclusively in first instants of the reaction (t<3 fm/c).

High pT azimuthal correlations: Elliptic flow (II)

Particle species

hierarchy of flow values:

v2meson > v2baryon at low pT

v2meson ≈ v2baryon at pT≈2. GeV/c

v2meson < v2baryon at higher pT

Simple v2 scaling behaviour

predicted by quark

recombination models:

v2 and pT normalized by #

of constituent quarks:

n = 2 mesons

n = 3 baryons

PHENIX Collab.

to appear in PRL

nucl-ex/0305013

High pT azimuthal correlations: Jet signals in Au+Au & p+p

dNpair/d for “trigger” (pT > 4GeV/c) & associated (pT = 2- 4 GeV/c) charg. hadrons:

Near-side peak: Au+Au = p+p.

Trigger hadrons (pT > 4GeV/c)

come from jets.

Away-side peak: Au+Au << p+p.

Back-to-back jets suppressed

in central Au+Au !

Periph.:

Central:

Red histogram: p+p (+flow)

Black points: Au+Au

Blue curve: flow contribution

High pT azimuthal correlations: Au+Au dijet signal disappearance

Ratio of Au+Au (- flow) over p+p azimuthal correlation “strengths”:

Increasing dissapearance of back-to-back correlation as a function of centrality.

Near-side peak: IAA~ 1

Away-side peak: IAA~ 0

Issue (8): IAA(periph)<1 ... is this physics ? an experimental bias ?

(Other independent measurements of correlation functions needed !)

High pT azimuthal correlations: jets in d+Au and p+p

Near- side: d+Au correlation strength and width similar to p+p (and Au+Au)

Increasing “underlying event”: p+p < d+Au(min.bias) < d+Au(central)

Away-side: d+Au peak broadens but small centrality dependence

Back-to-back jets do not disappear in central d+Au !

Unsuppressed (?) hard heavy-quark production

Indirect measurement via semileptonic open-charm decays: D e± X .

Within uncertainties, single electron Au+Au central spectra and x-section(*) consistent with Ncoll scaled p+p charm production:

Strong(*) medium effects on heavy flavor production precluded so far.

(*) at least as strong as for light-quark mesons.

(*) Charm production is intrinsically hard:

Ncoll scaling expected down to low pT

Possible reduction (1σ) at high pT ?

factor ~2 less suppression expected

for D than for p (RAA=0.2) in models of

medium-induced energy loss

Wait for results from hi-stat. Run-4.

[ Sean Kelly QM'04 ]

D.Kharzeev, E.Levin, L.McLerran

PLB 561, 93 (2003)

pQCD expectation

CGC prediction

RAANpart

Centrality dependence of suppression (I): Npart scaling ?

Suppression (w.r.t. Ncoll scaling) increases smoothly with centrality:

peripheral	central

PHENIX

nucl-ex/0304022,

submitted to PRL

Approximate Npart scaling in

semiquantitative agreement with

Color Glass Condensate prediction

High-energy heavy-ion physics program (in 4 plots)

1. Learn about 2 (so far unexplained) properties of the strong interaction: confinement, chiral symmetry breaking

as(Q2) ~1/ln(Q2/L2), L~200 MeV

3. Probe the properties

of the primordial

Universe (few μsec

after the Big Bang).

2. Study the phase diagram of QCD

matter (esp. produce & study the QGP)

4. Study the regime of non-linear (high density)

many-body parton dynamics at small-x (CGC).

(as=g2/4p)

Unsuppressed hard colorless production

“Control” observable: direct photons are clean, penetrating (directly coupled to partonic vertex, no fragmentation) non-hadronic hard probes.

Probes insensitive to colored final-state do show collision scaling at high pT:

pQCD incoherent parton scattering holds for hard processes in central Au+Au !

g NLO pQCD x Ncoll Vogelsang/CTEQ6 (M = 0.5 - 2.0 pT)

preliminary AuAu 200 GeV 0-10%

[ J.Frantz QM'04 ]

“ g (direct+decay) / g decay ”

The solutions of the theory must exhibit 2 “properties” observed in Nature (but not in the Lagrangian):

Confinement: quarks and gluons do not exist as isolated particles The elementary degrees of freedom are not observed free in Nature. the color electric field energy generated by an isolated quark is calculated to be truly infinite, due to the energy it creates in distant fields

Chiral symmetry breaking: The constituent quark masses are different of the current masses (~0 MeV).

David d'Enterria

2004-01-14T06:23:12