Hadronic Probes of dense matter at RHIC

From light to heavy flavors

Y. Akiba (RIKEN)

DNP/JPS ’05Kapalua, Hawaii, September 2005

The RHIC Experiments

RHIC

Probes of the evolution of the matter

Formation of dense matter

Hadronization

Thermal Freeze Out

tim

e

Chemical Freeze Out

Thermalization

Hadron spectrafemotoscopy

Hadron ratios

Quark number scaling of v2Anomalous baryonJ/Psi formation(?)

Jet quenching /jet tomographyHeavy quark energy lossJ/Psi suppression

Initial collision pQCD direct photonHeavy quark production

q(x), g(x)

DensityDeconfined(?)

EOSViscocitythermal

Tini

# of DOF

Recombination(?)

Tchem

B

Tfo

<T>

Elliptic flow (Heavy quark)Elliptic flow (light hadron)

Topics covered by this talk

Formation of dense matter

Hadronization

Thermal Freeze Out

tim

e

Chemical Freeze Out

Thermalization

Hadron spectra

Hadron ratios

Quark number scaling of v2Anomalous baryon

Heavy quark energy loss

Initial collisionHeavy quark production

q(x), g(x)

Density

EOSViscocitythermal

Recombination(?)

Tchem

B

Tfo

<T>Light flavor hadrons

Open heavy flavor

Elliptic flow (Heavy quark)Elliptic flow (light hadron)

Topics covered by the other speaker

Formation of dense matter

Hadronization

Thermal Freeze Out

tim

e

Chemical Freeze Out

Thermalization

J/Psi formation(?)

Thermal radiation

Jet quenching /jet tomography

J/Psi suppression

Initial collision pQCD direct photon q(x), g(x)

Enegy densityDeconfined(?)

thermal

Tini

# of DOF

Recombination(?)

They cover more initial stage of the evolution.

The interest of the field is moving towards the study of partonic matter using penetrating probes

Hadron spectra: Tfo and <bT>

Formation of dense matter

Hadronization

Thermal Freeze Out

tim

e

Chemical Freeze Out

Thermalization

Hadron spectra

Hadron ratios

n-quark scaling of v2Anomalous baryon

Heavy quark energy loss

Initial collisionHeavy quark production

q(x), g(x)

Enegy density

EOSViscocitythermal

Recombination(?)

Tchem

B

Tfo

<T>

Elliptic flow (Heavy quark)Elliptic flow (light hadron)

Hadron spectra – thermal freeze-out and radial flow

• Hadron spectra are well reproduced by thermal distribution with radial expansion (blast wave model)

• p/K/ spectra can be simultaneously fit with two parameters:Tfo: freezeout temp.T: expansion velocity

• Fit resultsTfo ~ 110 MeVT ~ 0.8 (<T> ~ 0.6)

Energy dependence of radial velocity

• Blast wave model fits well hadron spectra data of A+A collisions from AGS to RHIC

• The Fit results indicates that the expansion velocity increase with energy from <>~0.4 (AGS) to 0.6 (RHIC)

Exp

ansi

on v

eloc

ity

Tkin ~ 100 MeV<vT/c> ~ 0.4-0.6

RHIC

More data: strange baryon spectra

200 GeVAu+Au(STAR)

62.4 GeVAu+Au(STAR)

Thermal freeze-out of

Tch

: low hadronic cross sectionThey can freeze-out earlier

Tfo of is close to Tch. Still they have significant radial flow

Another evidence for early development of flow(?)

Particle ratios: Chemical equillibrium

• Thermal model reproduces hadron ratios.• Tch ~ 160 MeV, B ~ 30 MeV• Evidence for Chemical equillibrium

Pbar/p vs K-/K+ in wide rapidity range

In thermal model, pbar/p ratio measures baryon chemical potential B

The model descripbes pbar/p verus K-/K+ data well in wide rapidity range as well as the beam enery dependence with B= B(y) and T~170MeV only B controls the particle ratio

BRAHMS PRELIMINARY

BRAHMS

Elliptic flow

Formation of dense matter

Hadronization

Thermal Freeze Out

tim

e

Chemical Freeze Out

Thermalization

Hadron spectra

Hadron ratios

n-quark scaling of v2Anomalous baryon

Heavy quark energy loss

Initial collisionHeavy quark production

q(x), g(x)

Enegy density

EOSViscositythermal

Recombination(?)

Tchem

B

Tfo

<T>

Elliptic flow (Heavy quark)

Elliptic flow of light hadrons

Elliptic Flow: Evidence for rapid thermalization

• The matter produced at RHIC behaves like fluid. It “flows”.

• The flow is strong evidence for rapid thermalisation of the matter.

• Experimentally, the flow is measured as event anisotropy with respect to the reaction plane

• The pattern of the “flow” is described by hydrodynamic calculation of ideal fluid (no viscosity)

• Hydro-model needs very short thermalization time (<0.6 fm/c) to reproduce the data.

x

z

y

Non-central Collisions

Reaction plane

Reaction plane

Large Pressure Collective Flow

More elliptic flow data from RUN4

• More v2 data in– Wider Pt range– More identified hadrons

• At Low pT, hydro-model reproduces v2 of heavy particles (etc) well

• Strong Flow of multi-strange hadrons (small hadronic cross section) support that the flow develops at partonic stage

Elliptic Flow is stronger at RHIC

• Elliptic Flow is stronger in RHIC energy than in lower energies, and it is close to “hydrodynamic limit” of ideal fluid (no visocity) Nearly perfect fluid

Elliptic flow vs pT v2/ecc vs sqrt(s)

PHENIX(62 GeV)

PHENIX(200 GeV)

STAR(130GeV)

NA49

PHENIX200,62 GeV

NA49, CERES

But do all pictures fit together?

proton pionv2/ecc and pT spectra

Data vs Hydro-models comparison in PHENIX White Paper (NPA757(2005)184)

Summary of Hydro Summary of Hydro ResultsResults

Models forModels for

HadronHadron

PhasePhasevv22((ppTT,,mm))

ppTT

spectraspectra

YieldYield

or ratioor ratio

ViscousViscous

effecteffectCaveatCaveat

ChemicalChemical

EquilibriumEquilibrium YYeses YYeses** NNoo NNoo

* P (Pbar) yields* P (Pbar) yields

<< exp. data<< exp. data

PartialPartial

ChemicalChemical

EquilibriumEquilibriumNNoo YYeses** YYeses NNoo

*Only low p*Only low pTT for pi for pi

onsons

Hadronic Hadronic CascadeCascade YYeses YYeses YYeses YYeses**

*Kinetic approach*Kinetic approach•BoundaryBoundary

(QGP(QGPhadron)hadron)

““No-Go theorem”No-Go theorem”

Ruled out!Ruled out!

WINNER for hydro race at RHIC !Hybrid model (Ideal QGP fluid + dissipative hadron gas)by Teaney, Lauret, and Shuryak

A slide by T. Hirano (1WB6)

Possible solution (by Hirano) • The agreement between ideal hydro-model and t

he data is due to “accidental cancellation of two effect:– Perfect fluidity of sQGP core (stronger v2)– Dissipative hadronic corona (reduce v2)

• Caveat:– Detailed comparison between the hybrid model (3D h

ydro + hadron cascade) and the data is still forthcoming

• If the hybrid model can reproduce all data (hadron spectra, hadron ratios, and v2), this will be a big step forward to an “unified model” of A+A collisons at RHIC

• Will it also solve the long standing HBT puzzle?

Hadronization and recombination

Formation of dense matter

Hadronization

Thermal Freeze Out

tim

e

Chemical Freeze Out

Thermalization

Hadron spectra

Hadron ratios

Quark number scaling of v2Anomalous baryon

Heavy quark energy loss

Initial collisionHeavy quark production q(x), g(x)

Density

EOSViscocitythermal

Recombination(?)

Tchem

B

Tfo

<T>

Elliptic flow (Heavy quark)Elliptic flow (light hadron)

Anomalous p/ ratio

• A surprise: anomalous p/ ratio in intermediate pt (2 – 4 GeV/c)• The large p/ ratio can not be explained by usual fragmentation me

chanism

Large p/ ratio in 2-4 GeV/c

Recombination model

• Recombination model explains the anomalous p/p ratio by a simple idea:– pT(baryon) ~ 3 * pT(q)– pT(meson) ~ 2 * pT(q)

• For exponentially falling spectra, baryon is enhanced relative to meson

• The model well repdoduces baryon/meson ratios in intermediate pT (2<pT<5 GeV/c)

STAR Preliminary

√sNN=200 GeV 0-5% Au+Au/p+p

Baryon vs meson; multi-strange baryon

behaves like proton, while meson behaves like pion

The difference is due to baryon/meson, not due to the mass (M ~ Mp) Support for recombination

Multi-strange baryon ( show even stronger enhancement than or p.

The enhancement increases with strangnessCan this be explained?

Quark number scaling of v2(pT)

• Complicated hadron species dependence of v2(pT) is observed• Recombination models explain the pattern by a simple quark number

scaling:pT pT/n, v2 v2/n (meson: n=2, baryon: n=3)

More particles added to the scaling plot

solid: STARopen: PHENIX PRL91(03)

More data of v2 and RAA/R

CP seem to support recombination picture.

But a few questions remain- Entropy conservation- Where are gluons?- Two particle correlation with leading baryon

Also: Can recombination model be accommodated into hydro+cascade model?

EOSViscocitythermal

Heavy quark: probes of early stage

Formation of dense matter

Hadronization

Thermal Freeze Out

tim

e

Chemical Freeze Out

Thermalization

Hadron spectra

Hadron ratios

n-quark scaling of v2Anomalous baryon

Heavy quark energy loss

Initial collisionHeavy quark production q(x), g(x)

DensityEnergy lossmechanism

Recombination(?)

Tchem

B

Tfo

<T>

Elliptic flow (Heavy quark)Elliptic flow (light hadron)

thermalization

Measurement of open charm

• Direct measurement of D meson:D0KD+KD*D+ Unambiguous signal- Small S/B (~1/600 in d+Au)- Limited statistics

• Semi-leptonic method: De+X, ->X (BR~10%)+ Large signal+ High statistics- Background from light hadr

ons- Indirect measurement of D-

meson kinematics- Can not distinguish b/c sign

al

c c

0DK

0D

K

single leptonD e+X, X

DK, DK

+

D0 Signal by STAR

6

d+Au at 200 GeV (RUN3) Au+Au at 200 GeV (RUN4)

Open heavy quark measurement through leptons

• open heavy quarks are measured by the semi-leptonic (electron) decay channel.

• Lepton yield total charm yield

• Lepton pT specta charm/beauty specta

medium

g

g

s,d

e,

c

Semi-leptonic decay channel

PHENIX/STAR single lepton data

• PHENIXe (|y|<0.35) and (1.2<|y|<2.4)

p+p e, @ 200 GeVd+Au e, @ 200 GeVAu+Au e @ 200, 130 and 63 GeV

• STARe (|y|<1) by TPC(dE/dx)+TOF,EMCAL

p+p e @ 200 GeVd+Au e @ 200 GeVAu+Au e @ 200 GeV

Single lepton in p+p by PHENIX

Cross sections of e and are consistent

PHENIX p+p at 200 GeVe : y = 0 nucl-ex/508034 y = -1.65 preliminary

STAR data in p+p, d+Au

• Measured D-meson and single electron from charm in the same experiment.

• The cross section is consistent within uncertainties.

PRL94,062301

Au+Au: Binary Scaling of Electron Yield• dN/dy of “Non-photonic” electrons for pT > 0.8 GeV/c scales with Nc

oll – dN/dy ~ Ncoll

where 0.906 < < 1.042 within 90% C.L.– cc = Ncc/TAA= 622 ±57 (stat) ± 160 (sys) b

• Little nuclear modification of G(x), consistent with direct photon data.

PHENIX PRL94 082301 (2005)

Au+Au: higher statistics electron data from RUN4

• A surprise. Electrons from Heavy quark decay are suppressed at high pT!

• Non-photonic =Inclusive - Cocktail

• Curves:Binary scaled p+p reference

• Significant improvement compared to Run02 analysis

• Clear high pT suppression developing towards central collisions

Nuclear Modification Factor RAA

pp

AA

AAAA

dpd

T

dpNd

R

3

3

3

3

Large energy loss Challenge to theory

Single electron data indicates that heavy quark (charm) suffers substantial energy loss in the matter

The large suppression requires a very large parton density or large c-quark-medium cross section: a challenge to the energy loss models

Even b-quark is suppressed?

q_hat = 14 GeV2/fm (c)

q_hat = 4 GeV2/fm (c)

q_hat = 0 GeV2/fm

dNg / dy = 1000 (b+c)

dNg / dy = 1000 (c)

dNg / dy = 3500 (c)

R_AA of non-photonic electron

PHENIX STAR

Both experiments reports significant suppression at high pT.However, the p+p reference is different, and the invariant yield in Au+Au is also different by a factor ~2.The difference need to be resolved for comparison with data.

V2 of electron from Heavy quark decay

V2(pT) of electron from heavy quark decay after subtracting photonic background.

Data clearly shows substaintial v2 of electrons

v2 of D-mesons

Data at low pT favors models that charm quark itself flows

Even heavy quark flows in the matter

PHENIXPreliminary

Greco,Ko,Rapp: PLB595(2004)202

The matter is so strongly coupled that even heavy quarks flow

v2(D)=0.3 v2()

v2(D)=0.6 v2()

v2(D)=v2()

• A simple model of D-meson v2 function form (v2(D) = a*v2() is used to evaluate the strength of D-meson v2 from electron data.

• The comparison favors v2(D) ~ 0.6 * v2()

• Charm flows, but not as strong as light mesons.

• Drop of the flow strength at high pT. This can be due to b-

quark contribution.

Comparison of PHENIX and STAR data

Not shown were "30-40%" systematic errors.

STAR reported a very large v2(e) in pT= 2-5 GeV/c in QM05.PHENIX and STAR data does not agree.The difference needed to be resolved

Comparison with models

R. Rapp (reso)

AMPT =10mb

AMPT = 3 mb

The large single electron v2 requires resonances (Rapp) or large c-matter cross section (AMTP)The different results in high pT (pT>2 GeV) from the two experiments shouldbe resolved.

Summary (1)• Light hadron data provide strong evidence for

– Thermalized, expanding final state with Tfo~100 MeV and <bT>~0.6 (hadron spectra)

– Chemical equilibrium among hadrons with Tch~170 MeV and B~30 MeV (hadron ratios)

– Rapid thermalization (t<0.6 fm/c) and ideal hydro-dynamical evolution (Elliptic flow)

• Recombination model provides simple explanation of – anomolous (anti-)baryon/pion ratio– Quark number scaling of v2

• Challenge to theorists:– An unified description of all of the data is still absent. C

an hybrid model of 3D hydro+hadron cascade be the solution?

Summary (2)• New preliminary data on single electron from heavy quar

k decay bring two surprises– Large suppression at high pT: RAA~0.3-0.4– Large elliptic flow: v2(e) ~ 0.1 @ 1.5-2 GeV/c

• Charm energy loss and flow is strong evidence for very high density of the matter and rapid thermalization

• Challenge to the theorists:– The data requires very strong interaction between matter and ch

arm quark and very high parton density of the matter– Energy loss mechanism needed to be re-considered?

• Challenges to experiments:– Publish the final results of the data– PHENIX/STAR difference need to be resolved

Thank you for your attention