1

Probing Dense Partonic Matter at RHIC

Barbara Jacak

for thePHENIX Collaboration

Feb. 8, 2004

News from PHENIX

2

Outline

Characterizing plasmas with PHENIX Initial state

pQCD via direct photonsShadowing via RdA in d+AuInitial state multiple scattering in d+Au

ThermalizationElliptic flow dependence on particle type, √s productionCharm flow

Probes of the partonic stateHeavy quark energy lossAway-side jet modificationWhat baryons tell about coupling to the medium

3

Properties of plasmas

Plasma physicists always want to know (and so do we)pressure, viscosity, equation of state,thermalization time & extent

determine from collective behavior at RHIC Other useful plasma properties

radiation rate, collision frequency, conductivity, opacity, Debye screening length

what is interaction of q,g in the medum? need short wavelength strongly interacting

probe transmission probability

jet quenching via RAA high momentum q,g are our “external” probes!

4

PHENIX• Collision vertex and centrality

– Beam-Beam Counters (BBC)– Zero Degree Calorimeters (ZDC)

• Tracking of Charged particle– Drift Chambers (DC)– Pad Chambers (PC1, PC2, PC3)

• , K, p, d, ... ID by Time-Of-Flight– Start timing from BBC– Stop timing from

High resolution TOF detectors (TOF)TOF from Lead Scintillator EMCal (PbSc)

• Electron ID– Ring Image Cherenkov (RICH) detectors– EMCal (PbSc, PbGl)

• Photon (0, , ...)– EMCal (PbSc, PbGl)

• Muon– Muon Tracker (MuTr)

Cathode-strip readout chamber

– Muon Identifier (MuID)Streamer (Iarocci) tube and steel

5

Direct photons (p+p)

LO

NLO: BremsstrahlungpQCD works!

see talk of S. Bathe

6

Direct photons in Au+Au

pQCD works too (with nuclear Sa/A(xa,r) , TA(r) + observed 0

can reliably calculate rate & distribution of short wavelength probes of hot, dense partonic matter!

7

kT smearing?

data allow kT

smearing But, certainty

awaits higher statistics (currently being analyzed)

8

Charm production also calculable*

* total yield scales with Ncoll.

I will return to charm again

** there is a long-standing problem with c

nucl-ex/0409028

9

Charm via single e± in p+p

PHENIX preliminary

10

Single e± in √sNN = 62.4 GeV Au+Au

Compatible with <Ncoll> scaling

(PHENIX compared with ISR results for p+p)

PHENIX PRELIMINARY

11

Nuclear initial state effects

shadowing, saturation, multiple initial state scattering

PHENIX has a wide range of d+Au data

toolsshadowing via heavy quark or high pT hadron

productionPHENIX can probe saturation (super-shadowing…)

via rapidity dependence of hadron productionInitial state multiple scattering via dependence of

hadrons upon number of collisions per participant

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Probe cold nuclear matter by varying number of collisions.

Shadowing + initial semi-hard scatterings(Accardi, Gyulassy) reproduce the data

PRELIMINARY

Phys. Lett. B586, 244 (2004)

Very little room for additional dynamical shadowing at mid-y

Nuclear medium modifies initial state

d+Au: Cronin Effect (RdA>1): Multiple Collisions broaden pT spectrum

13

PRELIMINARY

Cronin effect for protons greater than for

would not expect this from initial state

partonic multiple scattering!

pp

AuAubinaryAuAuAA Yield

NYieldR

/

14

Need something else too…

Recombination?!

PROTON PRODUCTION IN D+AU COLLISIONS AND THE CRONIN EFFECT; HWA & YANG

Phys.Rev.C70:037901,2004

“Thermal

Thermal+Shower

Fragmentation (one jet)

Different jets.

“

15

Muon arms probe forward rapidity

Au

d

MUON ARMS

CAN DETECT:

*stopped muons from hadron decays

* hadrons which punch thru absorber and interact in arm

study central vs. peripheral in d+Au

see talk of Anuj Purwar

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d+Au central/peripheral

Aud

Au

1.5 < pT (GeV/c) < 4.0

Suppression at forward η and enhancement in the back η.

PTH = Punch Through HadronsHDM = Hadronic Decay Muon

PHENIX nucl-ex/0411054

x~0.2-0.3

x~0.2x10-3

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Compare with BRAHMS

Overall consistent.

nucl-ex/0411054

18

Color glass condensate?

Hadron Punch Through

Slightly better agreement with BRAHMS data“normal” shadowing cannot explain (R. Vogt hep-ph/0405060)

…could be sign of CGC

Kharzeev, hep-ph/0405045

Centrality, pT

dependence

~ correct

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But, recombination lurks…

shower + medium recombination → reductes soft parton density on deuteron side

Can explain fward-bward asymmetry AND RCP (protons) > RCP (mesons) at midrapidity.

Hwa, Yang and Fries nucl-th/0410111

BRAHMS data

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: does it fit with the non-strange mesons?

K+K- Au + Au @ √SNN = 200 GeV

Au+Au width & centroid as in PDG

nucl-ex/0410102

see talks of D. Pal and D. Mukhopadhyay

MixedBackground

Co

un

ts p

er 1

0 M

eV/c

2

e+e- invariant mass (GeV/c2)

e+e- @ d – Au, √s = 200 GeV

S ~ 120S/B = 1/4

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spectra & radial flow

mT – mass [GeV/c2]0 0.5 1 1.5 2 2.5 3

10-1

10-2

10-3

10-4

10-5

PHENIX preliminarysNN = 200 GeV d+Au, Min. Bias

e+e-

K+K-

Au + Au @ √sNN = 200 GeV

Au + Au @ √sNN = 200 GeV

d+Au yields & slopes: KK and ee consistent Au+Au: slopes nearly independent of Npart

but – this is at high pT

consistent with blast wave fit to , K, p

Tfo = 109 ± 2.6 MeV, T,max = 0.77 ± 0.004

nucl-ex/0410102

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v2 and scaling with nquark

stat. error onlysys. error <20% (62GeV) 15% (200GeV)

62.4 GeV Au+Au: preliminary200 GeV Au+Au, charged ,K,p PRL91, 182301 (2003) 0 : work in progress

v 2 /n

qu

ark

extend to

higher pT

pT /nquark [GeV/c]

62.4 GeV Au+Au:

scaling, v2/quark

similar to 200 GeV

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Collision energy dependence

smooth rise of v2 from AGS to SPS to RHIC energies.

v2 saturates: evidence for soft EOS? how soft?

Elliptic flow dv2/dpT vs √s

nucl-ex/0411040

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Are the v2 trends hydrodynamic?

use Buda-Lund model (nucl-th/0402036)particle emission from ellipsoidal expanding sourcev2 in terms of Bessel functions from Boltzmann distrib.

converting to transverse “rapidity”:

so v2 should have the form:

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0

( )

( )

I wv

I w

22 0 3 01 2

20 1 1

~ 1 ..T

T k Tk kv y m

T k m k m

22 0 3 01 2

20 1 1

~ 1 ..T

T k Tk kv y m

T k m k m

2fs

T m Ty k y m 2fsT m Ty k y m

we then define a “fine

structure” variable

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The data transform: 2fsT m Ty k y m 2fsT m Ty k y m

pT (GeV/c)

0.0 0.5 1.0 1.5 2.0 2.5 3.0

v 2

0.00

0.05

0.10

0.15

0.20

0.25

pK

s 200 GeVNNAu Au

0 1 2 3

v 2

0.00

0.05

0.10

0.15

0.20

s 200 GeVNNAu Au

p

fsTy

5 < Centrality < 30 %

K

(PHENIX)

(PHENIX)

(PHENIX)

0.0 0.5 1.0 1.5 2.0 2.5

v 2

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

fsTy

Kp

Hydro

Au Au data look like hydro!

(kaons a mystery, still)

scaling with also seen

supports scenario of rapid thermalizationKolb, et al

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Caveat: v2 & spectra vs. hydrodynamic models

proton pion

Hydro models:Teaney(w/ & w/oRQMD)

Hirano(3d)

Kolb

Huovinen(w/& w/oQGP)

nucl-ex/0410003

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How about heavy quarks? do they flow?

PHENIX measures v2 of non-photonic e±

electron ID in Au+Au via RICH + EMCALmeasure and subtract photonic sources using converter

nucl-ex/0502009

YES

v2 ≠ 0 at 90% confidence level

data consistent with heavy q thermalization

also “predicted” by Teaney

*but large errors; run4 will tell

Greco,Ko,Rapp.

PLB595, 202 (2004)

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Short wavelength probes of partonic matter

HOW is jet fragmentation modified by the medium? do heavy quarks lose energy as the light quarks do?

Kharzeev & Dokshitzer PLB519, 199 (2001): eloss smaller dead cone due to large mass decreases gluon radiationby ~20% at moderate pT

Djordjevic, Gyulassy, Wicks hep-ph/0410372: smallerdead cone, charm pT spectrum & B contribution cause RAA ~ 0.6-0.8 for 2.5< pT <4 GeV/cCronin effect & collective flow also important

Armesto, Dainese, Salgado, Wiedeman hep-ph/0501225 :smallerdead cone, g vs. q eloss differences → smaller RAA for c

Teaney: eloss significant if charm thermalizes!

coupling to the medium probes medium properties

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Non-photonic single electron spectra

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Use p+p single e± as reference → RAA

clear

evidence for

energy loss of

charm quarks

in central

Au + Au!

(NB likely to

also be some

e± from B decays)

RAA

pT (GeV/c)

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Consistent with light quarks?

RAA

pT (GeV/c)

q consistent w/ light quark eloss

non-pert.

effects on

“normal” g

radiation

data say:

same transport coefficient,

smaller hadron suppression

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jet probes of the medium

Hard scattered partons traverse the interesting stuff

Energy loss by induced gluon radiation

where does the energy go?

Modification of fragmentation outside the medium??

recombination with medium partons

radiated gluons nearby!

coneRFragmentation:

z hadron

parton

p

p

see talk of N. Ajitanand

33

correlation functions of two high pT hadrons

Elliptic flow component measured vs. BBC reaction plane

34

decompose to get jet pair distribution

Away-side jets broadened

non-Gaussian!

~2 dip at & peak at 1.25 rad around hard parton thru medium

integrating entire away side recovers jet partners

Casalderry, Shuryak, Teaney say 1.1 rad cone

hep-ph/0411315

35

Jet partner likely for trigger baryons as well as mesons! Same side: slight decrease with centrality for baryonsDilution from boosted thermal p, pbar?

Away side: partner rate as in p+p confirms jet source of baryons!“disappearance” of away-side jet into narrow angle for both baryons and mesons

identify triggers, count partnersnucl-ex/0408007

36

What’s going on?

Thermal quark recombination

Radiated gluons are collinear (inside jet cone)

Increases partner yield

Fries, Bass & Muellernucl-th/0407102

Meson triggerbaryon

Dilutes jet partner yield

37

Jet partner distribution on trigger side

Corrected to jet yield according to fragmentation symmetric in Partner spectrum flatter, as expected for jet sourcePartners soften in most central collisions

Jet partners

Inclusive

nucl-ex/0408007

38

Compare to hard-soft recombination

trigger & associatedHwa & Yang nucl-th/0407081

Soft-hard recomb. also explains baryon Cronin effect! No jet-correlated medium flow

39

Conclusions

Direct & hard processes in AuAu calculable in pQCDwe observe nuclear shadowing at RHICno room for saturation at mid-y; forward: could bebaryon mysteries already present in d+Au

Hadron v2 trends support rapid thermalization hypothesis

theorists have homework to see how soft is EOSheavy quarks do flow (and thermalize…)

Heavy quarks lose energy in the medium!jet fragmentation is modified; lost energy excites the mediumbaryon formation in/near medium in A+A and d+A

Opacity/collision frequency, screening length await run4 analysis completion (+ theory work!)

radiation rate (low mass leptons, soft ) → PHENIX upgrades

40

backup slides

41

Compare to Au+Au

RAA as expected in Au+Au; d+Au slightly enhanced

p RAA scales with Ncoll in Au+Au, but higher than p+p

PRELIMINARY

42

Turn to nuclear collisions: single particles

h/0 ratio shows baryons enhanced for pT < 5 GeV/c

PRELIMINARY

43

yields

0 100 200 300 0 100 200 300

dN/d

y

<Npart> <Npart>(d

N/d

y) /

(2<

Np

art>

)

200 GeV d+Au (preliminary)

200 GeV Au+Au w/ centrality cut

200GeV Au+Au Min. Bias

Hor. bar : stat. err.

Box : total sys. err.

rapid rise in /participant in peripheral collisions then ~ constant per participant - as for kaons

nucl-ex/0410102

44

Interacting Hadrons

Interacting Hadrons (tail)

Stopped muons (peak)

PH

3 GeV

1 GeV

3 GeV

MuID

Gap (Layer) 0 1 2 3 4

ste

el

Hadrons interactelectromagneticallyAND strongly.

45

Muons from Light Meson Decays

Muon event collision vertex distribution

Muondetector

absorber

Muon pT ~ 0.85 parent pT

η > 0

Det

ecto

r

• D c = 0.03 cm Decays before absorber• c = 780 cm Most are absorbed, but some decay first • K c = 371 cm Most are absorbed, but some decay firstγcτ >> 80cm → Decay Probability nearly constant between nosecones

46

FONLL Predictions

Mateo Cacciari provided a prediction using the Fixed Order Next Leading Logarithm pQCD approach

His calculation agrees perfectly with our “poor man’s” HVQLIB+PYTHIA predictions

Data exceed the central theory curve by a factor of 2-3

Possible explanations:NNLO contribution Fragmentation mechanisms

need to be studied in more details

47

centrality dependence?

need to complete analysis of run4 data… first glimpse

48

Pions in 3 detectors in PHENIX

Charged pions from TOF

Neutral pions from EMCAL

Charged pions from RICH+EMCAL

Cronin effect gone at pT ~ 8 GeV/c

49

Subtract the underlying event

CARTOON

flow

flow+jet dN

Ntrig d

includes ALL triggers(even those with no

associated particles inthe event)

jet Measure with mixed events;Collective flow causes another correlation in them:

B(1+2v2(pTtrig)v2(pT

assoc)cos(2))

associated particles with non-flow angular

correlations -> jets!

1

combinatorial background large in Au+Au!

50

2 particle correlations

Select particles with pT= 2.5-4.0GeV/c

Identify them as mesons or baryons viaTime-of-flight

Find second particle with pT = 1.7-2.5GeV/c

Plot distribution of the pair opening angles;integrate over 55°

51

Thermalization? particle ratios and spectra

consistent with strongly expanding thermalized source

observed strangeness production complete chemical equilibrium

/K/p measurement in aBroad pt range

Statistical fit:Tch~ 160MeV, s~1.0Strangeness saturation at RHIC?

stronger radial flow at RHIC?

Exp

ansi

on v

eloc

ity

Tkin ~ 100 MeV<T> ~ 0.5

Chemical freezeout

Thermal freezeout

RHIC

52

HBT vs. hydro models

Nobody gets HBT right!

Origin of the “HBT puzzle”

Generic explanation: Nobody does freezeout of final state right

Another explanation:Maybe we’re fooled by the extraction of the radius parameters somehow

NB: Rside source transverse radius!

53

Empirical energy loss from dataF

ract

iona

l ene

rgy

loss

For power-law spectrum with A/pT

n

(we find n= 8.1 in pp)

Final spectrum = initial - <fractional shift>

<shift> due to eloss of parent partonParent pT would be:pT’ = (1+S) pT(pp)

Fractional energy loss:Sloss = 1 - 1/(1+S)

10 GeV: E/x ~ 0.5 GeV/fm

54

State-of-Art; Zooming into low pT

Most realistic calculationIncluding all the contributions

We may be able to see QGP contribution in 1-3GeV/c in Run4!

Thanks to Ralf Rapp for providing theoretical points!

55

Results (RAA)

Photon RAA is consistent with unity over all the centrality compared to 0 results.Clear evidence of that the yield follows thickness-scaled hard scatteringp-p reference from NLO pQCD Calculation0 RAA decreases to ~0.2 at Npart=320

Dotted line shows uncertainty of thickness functionError bars show total error (systematics + statistical) except thickness function error

56

Centrality (in)dependence in d+Au collisions

PHENIX PRELIMINARY

PHENIX PRELIMINARYPHENIX PRELIMINARY

PHENIX PRELIMINARY

1/T A

B1/

T AB

1/T A

B1/

T AB

1/T

ABE

dN/d

p3 [m

b G

eV-2]

1/T

ABE

dN/d

p3 [m

b G

eV-2]

1/T

ABE

dN/d

p3 [m

b G

eV-2]

1/T

ABE

dN/d

p3 [m

b G

eV-2]

57

Does Cronin enhancement saturate?

A different approach:

Intrinsic momentum broadening in the excited projectile proton:

hpA: average number of collisions:

X.N.Wang, Phys.Rev.C 61 (2000): no upper limit.

Zhang, Fai, Papp, Barnafoldi & Levai, Phys.Rev.C 65 (2002): n=4 due to proton d dissociation.

58

Jets in PHENIX

Trigger:hadron with pT > 2.5 GeV/cBiased, low energy, high z jets!

Plot of associated partnersCount associated lower pT

particles for each trigger “conditional yield”

Make correlation functions→ disentangle flow and jet contributions

trigger2 particle correlationsnear side < 90°Partner from same jet

away side > 90° opposing jet

59

Initial state: p+p collisions

p-p PRL 91 (2003) 241803

Good agreementwith NLO pQCD

2

/( , )

a Nf x Q

2

/( , )ch a

D z Q

Parton distribution functions

Fragmentation functions

0

0 well described by pQCD and usual fragmentation functions

To generalize for nuclei:fa/N(xa,Q2,r) fa/N(xa,Q2) .

Sa/A(xa,r) .

tA(r)

Nuclear modification to structure function (shadowing, saturation, etc.)

Nuclear thickness function

60

pQCD in Au+Au? direct photons

[w/ the real suppression]

( pQCD x Ncoll) / background Vogelsang/CTEQ6

[if there were no suppression]

( pQCD x Ncoll) / ( background x Ncoll)

Au+Au 200 GeV/A: 10% most central collisions

[]measured / []background = measured/background

Preliminary

Probe calculation works!

pT (GeV/c)

61

USA Abilene Christian University, Abilene, TXBrookhaven National Laboratory, Upton, NYUniversity of California - Riverside, Riverside, CAUniversity of Colorado, Boulder, COColumbia University, Nevis Laboratories, Irvington, NYFlorida State University, Tallahassee, FLFlorida Technical University, Melbourne, FLGeorgia State University, Atlanta, GAUniversity of Illinois Urbana Champaign, Urbana-Champaign, ILIowa State University and Ames Laboratory, Ames, IALos Alamos National Laboratory, Los Alamos, NMLawrence Livermore National Laboratory, Livermore, CaUniversity of New Mexico, Albuquerque, NMNew Mexico State University, Las Cruces, NMDept. of Chemistry, Stony Brook Univ., Stony Brook, NYDept. Phys. and Astronomy, Stony Brook Univ., Stony Brook, NY Oak Ridge National Laboratory, Oak Ridge, TNUniversity of Tennessee, Knoxville, TNVanderbilt University, Nashville, TN

Brazil University of São Paulo, São PauloChina Academia Sinica, Taipei, Taiwan

China Institute of Atomic Energy, BeijingPeking University, Beijing

France LPC, University de Clermont-Ferrand, Clermont-FerrandDapnia, CEA Saclay, Gif-sur-YvetteIPN-Orsay, Universite Paris Sud, CNRS-IN2P3, OrsayLLR, Ecòle Polytechnique, CNRS-IN2P3, PalaiseauSUBATECH, Ecòle des Mines at Nantes, Nantes

Germany University of Münster, MünsterHungary Central Research Institute for Physics (KFKI), Budapest

Debrecen University, DebrecenEötvös Loránd University (ELTE), Budapest

India Banaras Hindu University, BanarasBhabha Atomic Research Centre, Bombay

Israel Weizmann Institute, RehovotJapan Center for Nuclear Study, University of Tokyo, Tokyo

Hiroshima University, Higashi-HiroshimaKEK, Institute for High Energy Physics, TsukubaKyoto University, KyotoNagasaki Institute of Applied Science, NagasakiRIKEN, Institute for Physical and Chemical Research, WakoRIKEN-BNL Research Center, Upton, NYRikkyo University, TokyoTokyo Institute of Technology, TokyoUniversity of Tsukuba, TsukubaWaseda University, Tokyo

S. Korea Cyclotron Application Laboratory, KAERI, SeoulKangnung National University, KangnungKorea University, SeoulMyong Ji University, Yongin CitySystem Electronics Laboratory, Seoul Nat. University, SeoulYonsei University, Seoul

Russia Institute of High Energy Physics, ProtovinoJoint Institute for Nuclear Research, DubnaKurchatov Institute, MoscowPNPI, St. Petersburg Nuclear Physics Institute, St. PetersburgSt. Petersburg State Technical University, St. Petersburg

Sweden Lund University, Lund

12 Countries; 58 Institutions; 480 Participants*

*as of January 2004