Some results obtained at RHIC

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A.Litvinenko July 2008,

Some results obtained at RHICSome results obtained at RHIC

Anatoly Litvinenko

litvin@moonhe.jinr.ru

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Outline.Outline.

Introduction RHIC. Short introdaction Why we study nuclei-nuclei collisions?

A few definitions. What can we expect from theory Properties of produced hadronic matter (observables)

Energy density equilibration time (elliptic flow) jet qenching Resonances melting (Debye scrinig)

Conclusions

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RRelativistic elativistic HHeavy eavy IIon on CCollider (ollider (RHICRHIC))

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2 rings, 3.8 km circumference.2 rings, 3.8 km circumference.Polarized p and Nucleus up to Au.Polarized p and Nucleus up to Au.

Top energies (each beam):Top energies (each beam):100 GeV/nucleon Au-Au. 250 GeV polarized p-p.100 GeV/nucleon Au-Au. 250 GeV polarized p-p.

NIM, v.499, p. 235-880, (2003)

GeV200SNN

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Why the collisons of heavy nuclei is interesting?

Let us see on the space – time picture of collision

pre-collision QGP (?) and parton production

hadron production

hadron reinteraction

QCD phase diagram

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The QGP in the early universe

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The QGP in the early universe

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What kind of transition is predicted by lattice QCD

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Rough estimation – ideal mass less gas

Bosons -- 1- degree of freedom:

423

02

4B T

301)T/exp(d

1).Fm(

8

7T

301)T/exp(d

1).Fm( 4

23

02

4F

Fermions -- 1- degree of freedom:

2 quarks

3 quarks

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Lattice QCDQualitative

GeV17.0Tc

F. Karsch, Lecture Notes in Physics 583 (2002) 209.

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42

42

3037

30}82

87

3222{ TTcscqsfSB

42

42

305.47

30}82

87

3223{ TTcscqsfSB

For

GeVTc 17.0

3/ 26.12 fmGeVN SBf 3/ 6.13 fmGeVN SBf

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Questions to be answered (experiment)

1.What is the value of energy density?2. If the statistical equilibration is achieved? 3.Observables and hadronic matter properties.

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Rapidity

Lorens boost

) (

) (

z

zz

pEE

Epp

zp -

ln 21

E

pEy z

0zz

y y -1 1

ln 21

p -

ln 21

p -

ln 21

EpE

EpE

y zz

Pseudorapidity

2)/ln(21

- )cos-p(1)cos1(

ln 21

pcos -

cosln

21

tgp

EpE

y

Transverse mass 22TT pmm

)(

)(

yshmp

ychmE

TL

T

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Stopping power

Net baryons distribution

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73 ± 6GeV / nucleon

Stopping power

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b2R ~ 15 fm

Centrality determination

Participant Region Spectators

Spectators

Central collision, b = 0 Peripheral collisoin, b 2R

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R

geo Rbdb2

0

2)2(2

Centrality classification

Value of impact parameter

Geometrical cross section

fm 42 b

In percent from the geometrical cross section

% 50 40 Centrality

Corresponds to the region impact parameter

fm 9.5 (15)fm 0.63 )2( 4.0min Rb

fm 10.6 (15)fm 0.71 )2( 5.0max Rb

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Spectator distribution for different centrality

ZDC – Zero Degree Calorimeter

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QUESTION IQUESTION I

Can we achieved enough energy densityin nuclei-nuclei collisions ?

Can we make some conclusion about from experiment?

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dydE

SSdy

mdNT

Form

TFormBj

..

1)(

Historically energy density was estimated using final dy

dET

cfmForm /. 13./ 5.1; 5;: fmGeVBjGeVSAuAuAGS NN 3./ 9.2; 17;: fmGeVBjGeVSPbPbSPS NN

3./ 4.5; 200 ;: fmGeVBjGeVSAuAuRHIC NN

Energy density and Bjorken equation

for

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Energy density but

crossing time Form.τbe to have /2 R

130 2 fm/c.γ/R RHIC - 61 2 fm/c.γ/RSPS - /3.5 /2 - cfmRAGS

Energy density is determined using final state

For TForm m/ and GeV 6.0 Tm / 0.35 cfmForm

/ 15 3fmGeVBj

init.final BjBj

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Can we achieved enough energy densityin nuclei-nuclei collisions ?

Can we make some conclusion about from experiment?

Yes! Bjorken equation

QUESTION IQUESTION I

33. GeV/fm 1GeV/fm 15)( FormBj

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QUESTION IIQUESTION II

Is equilibrium state of hot and dense hadronic matter achieved?

What is conclusions about from experiment?

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The answer is not evident.

Asymptotic freedom

High energy density Small coupling constant

Big equilibration time

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elliptic flowelliptic flow

Coordinate space asymmetry momentum space anisotropy

22x

22x

2 y

y

pp

ppv

Space eccentricity Elliptic flow

...)2cos2cos21(2

121

vv

d

dN

22

22

yy

xx

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Elliptic flowElliptic flow

For big value of elliptic flow you need save space anisotropy for a long enough timeThe value of elliptic flow is sensitive to the Equation of State (EoS)

Importance of elliptic flowImportance of elliptic flow

1. Give information about equilibration time2. Give information about EoS

On the next slides shown how ensemble of free streaming particles lost space eccentricity

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TIME = 0 fm/c, 0.7

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TIME = 1 fm/c, 0.6

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TIME = 2 fm/c, 0.5

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TIME = 3 fm/c, 0.3

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elliptic flow and space eccentricityelliptic flow and space eccentricity

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Sensitivity to nuclear EoSSensitivity to nuclear EoS

Science, Vol 298, Issue 5598, 1592-1596, 22 November 2002Determination of the Equation of State of Dense Matter Pawel Danielewicz, Roy Lacey, William G. Lynch

Directed Flow: Elliptic flow:

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QUESTION IIQUESTION II

Is equilibrium state of hot and dense hadronic matter achieved?

What is conclusions about from experiment?

The strong indication that YES.

/ 1 cfmTherm

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Some designations

sQGP for strongly-interacting Quark-Gluon Plasma

It is not reasons to expect strong changes in observables because the transition is crossover

Commonly accepted:

QGP, pQGP,wQGP for weakly-interacting Quark-Gluon Plasma

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Observables and space time structureObservables and space time structure of of Heavy ion collisionsHeavy ion collisions

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Observables and space time structureObservables and space time structure of of Heavy ion collisionsHeavy ion collisions

Production of hard particles: jets heavy quarks direct photonsCalculable with the tools of perturbative QCD

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Observables and space time structureObservables and space time structure of of Heavy ion collisionsHeavy ion collisions

Production of semi-hard particles: gluons, light quarks relatively small momentum: make up for most of the multilplicity

cGeVpT / 21

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Observables and space time structureObservables and space time structure of of Heavy ion collisionsHeavy ion collisions

Thermalizationexperiment suggest a fast thermalization (remember elliptic flow)but this is still not undestood from QCD

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Observables and space time structureObservables and space time structure of of Heavy ion collisionsHeavy ion collisions

Quark gluon plasma

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Observables and space time structureObservables and space time structure of of Heavy ion collisionsHeavy ion collisions

Hot hadron gas

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Particle ratio and sParticle ratio and statistical modelstatistical models

These models reproduce the ratios of particle yields with only two parameters

One assumes that particles are produced by a thermalized system with temperature T and baryon chemical potential

The number of particles of mass m per unit volume is :

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Particle ratios and sParticle ratios and statistical modelstatistical models

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N/ ratio shows baryons enhanced for pT < 5 GeV/c

One more observable. Particle ratios

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JET Quenching

Modification of Jet property in AA collisions because partons propagating in colored matter lose energy.

One of the possible observableTp

Was predicted in a lot of works. Some of them (not all) are:

1

0)(Pd

J.D.Bjorken (1982), Fermilab – PUB – 82 – 059 - THY.M.Gyulassy and M.Palmer, Phys.Lett.,B243,432,1990.X.-N.Wang, M.Gyulassy and M.Palmer, Phys.Rev.,D51,3436,1995.R.Baier et al., Phys.Lett.,B243,432,1997.R.Baier et al., Nucl.Phys.,A661,205,1999

The suppression of the high- hadrons In AA collisions

Jet: A localized collection of

hadrons which come from a fragmenting parton

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High pT (> ~2.0 GeV/c) hadrons in NN

h

h

A

abc

dParton distribution functions

Hard-scattering cross-section

Fragmentation Function

B

)Q,x(f 2aaa/A )Q,x(f 2

bbb/B cdabd )Q,z(D 2ddd/h

d,c,b,ahXABd

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High pT (> ~2.0 GeV/c) hadrons in NN

h

h

A

abc

dParton distribution functions

Hard-scattering cross-section

Fragmentation Function

B

)Q,x(f 2aaa/A )Q,x(f 2

bbb/B cdabd )Q,z(D 2ddd/h

d,c,b,ahXABd

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Nuclear modification factor

is what we get divided by what we expect.is what we get divided by what we expect.

NN

biaryAAAA d

N/dR

From naive picture

AAR

1

0 d

*d

z

z)(Pd (...)f b/B(...)f a/A

(...)f b/B(...)f a/A

)Q,z(D 2d

*dd/h

)Q,z(D 2d

*dd/h

cdabd

cdabd

AAR

Suppression of high-pt hadrons. Qualitatively.

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First data in first RHIC RUN

Jet Quenching ! Great!

But (see the next slide)

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Nuclear modifications to hard scattering

Large Cronineffect at SPSand ISRSuppression at RHIC

Is the suppression due to the medium?(initial or final state effect?)

RAA ( pT ) d2N AA /dpT d

TAA d2 NN /dpT d

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Au+Au @ sNN

= 200 GeV d+Au @ sNN

= 200 GeV

preliminary

Au+Au @ sNN

= 200 GeV d+Au @ sNN

= 200 GeV

preliminary

Au+Au @ sNN

= 200 GeV d+Au @ sNN

= 200 GeV

preliminary

Au+Au @ sNN

= 200 GeV d+Au @ sNN

= 200 GeV

preliminary

• Nice picture! Isn’t it?

Again Au+Au and d+Au

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The matter is so opaque that even The matter is so opaque that even

a 20 GeV a 20 GeV 00 is stopped is stopped..

• Suppression is very strong (RAA=0.2!) and flat up to 20 GeV/c• Common suppression for 0 and it is at partonic level• > 15 GeV/fm3; dNg/dy > 1100

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The matter is so dense that even heavy quarks are stopped

Even heavy quark (charm) suffers substantial energy loss in the matter

The data provides a strong constraint on the energy loss models.

The data suggest large c-quark-medium cross section; evidence for strongly coupled QGP?(3) q_hat = 14 GeV2/fm

(2) q_hat = 4 GeV2/fm

(1) q_hat = 0 GeV2/fm

(4) dNg / dy = 1000

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If there are any other observables for Jet Quenching?

Correlation of trigger particles 4<pT<6.5 GeV withassociated particles 2<pT<pT,trig

Associated particles

Near side jetTrigger particle

Away side jet

Yes! Back to Back Jets correlation.

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In-plane In-plane

Out-of-plane

Out-of-plane

Back to Back Jets correlation.Back to Back Jets correlation.Dependence from reaction plane.Dependence from reaction plane.

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Jet tomography

20-60%

STAR Preliminry

20-60%

Back-to-back suppression depends on the reaction plane orientation

In-plane

Out-plane

energy loss dependence energy loss dependence on the path length!on the path length!

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The matter is so dense that it The matter is so dense that it modifies the shape of jetsmodifies the shape of jets

• The shapes of jets are modified by the matter.– Mach cone?– Cerenkov?

• Can the properties of the matter be measured from the shape?– Sound velocity– Di-electric

constant• Di-jet tomography is

a powerful tool to probe the matter

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Resonances melting (Debye scrinig)

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One more results from lattice QCD

heavy-quark screening mass

r/)rexp(~)r(

In EM plasma it is well known Debye screening

T/1~r/1 D

/J -- suppression

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The matter is so dense that it melts(?) J/ (and regenerates it ?)

CuCu

200 GeV/c

AuAu

200 GeV/c

dAu

200 GeV/c

AuAuee

200 GeV/c

CuCuee

200 GeV/c

J/’s are clearly suppressed beyond the cold nuclear matter effect

The preliminary data are consistent with the predicted suppression + re-generation at the energy density of RHIC collisions.

Can be tested by v2(J/)?

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SummarySummary

o RHIC has produced a strongly interacting,RHIC has produced a strongly interacting, partonic state of dense matterpartonic state of dense matter

/ 15 3fmGeVBj

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SummarySummary

o The matter is so dense that even heavy quarks are stopped

(3) q_hat = 14 GeV2/fm

(2) q_hat = 4 GeV2/fm

(1) q_hat = 0 GeV2/fm

(4) dNg / dy = 1000

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SummarySummary

o The matter is so strongly coupled that even heavy quarks flow

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SummarySummary

o The matter is so dense that it melts(?) J/ (and regenerates it ?)

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SummarySummary

o The matter modifies jets

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SummarySummary

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The matter may melt but regenerate J/’s

Put the results together

The matter is denseThe matter is strongly coupled

The matter is hot

The matter modifies jets

> 15 GeV/fm3

dNg/dy > 1100

Tave = 300 - 400 MeV (?)PHENIX preliminary

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Backup slidesBackup slides

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• The first promising result of direct photon measurement at low pT from low-mass electron pair analysis.

• Are these thermal photons? The rate is above pQCD calculation. The method can be used in p+p collisions.

• If it is due to thermal radiation, the data can provide the first direct measurement of the initial temperature of the matter.

• T0max ~ 500-600 MeV !?

T0ave ~ 300-400 MeV !?

The matter is so hot that it emits (thermal?) photon copiously

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Theoretical explanation

Comparison to model calculations with and without parton energy loss:

Numerical values range from ~ 0.1 GeV / fm (Bjorken, elastic scattering of partons)~several GeV / fm (BDMPS, non-linear interactions of gluons)

Too many approaches.We need additional data!

2.0~Rand,p~d AuAu8

T

2.0~p/p

Estimation from data

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Initial state effects (test experiment d+Au)

Suppression in central Au+Au due to final-state effects

/h

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Binary scaling. Is it work?

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How about suppression for protons?

pcollccollCP )N/dN/()N/dN(R New

Close to nuclear mod. factor, because no suppression for peripheral coll.

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Jets composition as measured by STAR

Kirill Filimonov, QM’04

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[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

pT (GeV/c)

Binary scaling. Is it work?

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Theoretical explanation

Comparison to model calculations with and without parton energy loss:

Numerical values range from ~ 0.1 GeV / fm (Bjorken, elastic scattering of partons)~several GeV / fm (BDMPS, non-linear interactions of gluons)

Too many approaches.We need additional data!

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If is there space for Color Glass Condensate or only Cronin Effect?

May be. Look at the BRAMS DATA

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