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Some results obtained at RHIC. Anatoly Litvinenko. [email protected] 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)

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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


Relativistic Heavy Ion Collider (RHIC)


2 rings, 3.8 km circumference.

Polarized p and Nucleus up to Au.

Top energies (each beam):

100 GeV/nucleon Au-Au. 250 GeV polarized p-p.

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


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 reinteraction

hadron production

QCD phase diagram





Rough estimation – ideal mass less gas

Bosons -- 1- degree of freedom:

Fermions -- 1- degree of freedom:

2 quarks

3 quarks


Qualitative

Lattice QCD

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



Questions to be answered (experiment)

  • What is the value of energy density?

  • If the statistical equilibration is achieved?

  • Observables and hadronic matter properties.


Rapidity

Lorens boost

Pseudorapidity

Transverse mass


Stopping power

Net baryons distribution


Stopping power

73 ± 6GeV / nucleon


b

2R ~ 15 fm

Centrality determination

Participant Region

Spectators

Spectators

Peripheral collisoin, b  2R

Central collision, b = 0


Centrality classification

Geometrical cross section

  • Value of impact parameter

  • In percent from the geometrical cross section

Centrality

Corresponds to the region impact parameter


Spectator distribution for different centrality

ZDC – Zero Degree Calorimeter


QUESTION I

Can we achieved enough energy density

in nuclei-nuclei collisions ?

Can we make some conclusion about

from experiment?


Energy density and Bjorken equation

Historically energy density was estimated using

final

for


Energy density

but

crossing time

For

and

Energy density is determined using final state


QUESTION I

Can we achieved enough energy density

in nuclei-nuclei collisions ?

Can we make some conclusion about

from experiment?

Yes! Bjorken equation


QUESTION II

Is equilibrium state of hot and

dense hadronic matter achieved?

What is conclusions about

from experiment?


The answer is not evident.

Asymptotic freedom

Big equilibration

time

Small coupling

constant

High energy density


Elliptic flow
elliptic flow

Elliptic flow

Space eccentricity

Coordinate space asymmetry  momentum space anisotropy


Elliptic flow

  • For big value of elliptic flow you need save space

    anisotropy for a long enough time

  • The value of elliptic flow is sensitive to the

    Equation of State (EoS)

Importance of elliptic flow

  • Give information about equilibration time

  • Give information about EoS

On the next slides shown how ensemble of

free streaming particles lost space eccentricity







Sensitivity to nuclear eos
Sensitivity 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:


QUESTION II

Is equilibrium state of hot and

dense hadronic matter achieved?

What is conclusions about

from experiment?

The strong indication that YES.


Some designations

It is not reasons to expect strong changes

in observables because the transition is crossover

Commonly accepted:

sQGP

for strongly-interacting Quark-Gluon Plasma

QGP, pQGP,wQGP

for weakly-interacting Quark-Gluon Plasma


Observables and space time structure

of Heavy ion collisions


Observables and space time structure

of Heavy ion collisions

  • Production of hard particles:

  • jets

  • heavy quarks

  • direct photons

  • Calculable with the tools of perturbative QCD


Observables and space time structure

of Heavy ion collisions

  • Production of semi-hard particles:

  • gluons, light quarks

  • relatively small momentum:

  • make up for most of the multilplicity


Observables and space time structure

of Heavy ion collisions

  • Thermalization

  • experiment suggest a fast thermalization

    (remember elliptic flow)

  • but this is still not undestood from QCD


Observables and space time structure

of Heavy ion collisions

  • Quark gluon plasma


Observables and space time structure

of Heavy ion collisions

  • Hot hadron gas


Particle ratio and statistical models

  • One assumes that particles are produced by a thermalizedsystem with temperature T and baryon chemical potential

  • The number of particles of mass mper unit volume is :

These models reproduce the ratios of particle yields withonly two parameters


Particle ratios and statistical models


One more observable. Particle ratios

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


JET Quenching

Jet: A localized collection of

hadrons which come from a fragmenting parton

Modification of Jet property in AA collisions because partons

propagating in colored matter lose energy.

One of the possible observable

The suppression of the high- hadrons In AA collisions

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

  • 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


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

h

d

A

Parton distribution functions

a

b

c

Hard-scattering

cross-section

B

h

Fragmentation Function


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

h

d

A

Parton distribution functions

a

b

c

Hard-scattering

cross-section

B

h

Fragmentation Function


Suppression of high-pt hadrons. Qualitatively.

Nuclear modification factor

From naive picture

is what we get divided by what we expect.


First data in first RHIC RUN

Jet Quenching ! Great!

But (see the next slide)


Nuclear modifications to hard scattering
Nuclear modifications to hard scattering

Large Cronin

effect at SPS

and ISR

Suppression at RHIC

Is the suppression due to the medium?

(initial or final state effect?)


Au+Au @ sNN = 200 GeV

Au+Au @ sNN = 200 GeV

Au+Au @ sNN = 200 GeV

Au+Au @ sNN = 200 GeV

d+Au @ sNN = 200 GeV

d+Au @ sNN = 200 GeV

d+Au @ sNN = 200 GeV

d+Au @ sNN = 200 GeV

preliminary

preliminary

preliminary

preliminary

Again Au+Au and d+Au

  • Nice picture! Isn’t it?


The matter is so opaque that even a 20 gev p 0 is stopped
The matter is so opaque that even a 20 GeV p0 is stopped.

Suppression is very strong (RAA=0.2!) and flat up to 20 GeV/c

Common suppression for p0 and h; it is at partonic level

e > 15 GeV/fm3; dNg/dy > 1100


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

(1) q_hat = 0 GeV2/fm

(4) dNg / dy = 1000

(2) q_hat = 4 GeV2/fm

(3) q_hat = 14 GeV2/fm


Trigger particle

Near side jet



Away side jet

If there are any other observables for Jet Quenching?

Yes! Back to Back Jets correlation.

Associated particles

Correlation of

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


Back to Back Jets correlation.

Dependence from reaction plane.

Out-of-plane

In-plane

In-plane

Out-of-plane


STAR Preliminry

20-60%

20-60%

Jet tomography

Out-plane

Back-to-back suppression depends on

the reaction plane orientation

In-plane

energy loss dependence

on the path length!


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


Resonances melting (Debye scrinig)


One more results from lattice QCD

heavy-quark screening mass

-- suppression

In EM plasma it is well known Debye screening


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

J/y’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/y)?

dAu

mm

200 GeV/c

AuAu

mm

200 GeV/c

CuCu

mm

200 GeV/c

AuAu

ee

200 GeV/c

CuCu

ee

200 GeV/c


Summary

  • RHIC has produced a strongly interacting,

  • partonic state of dense matter


(1) q_hat = 0 GeV2/fm

(4) dNg / dy = 1000

(2) q_hat = 4 GeV2/fm

(3) q_hat = 14 GeV2/fm

Summary

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


Summary

  • The matter is so strongly coupled

  • that even heavy quarks flow


Summary

  • The matter is so dense that it melts(?)

  • J/y (and regenerates it ?)


Summary

  • The matter modifies jets



Put the results together
Put the results together

The matter is strongly coupled

The matter is dense

  • > 15 GeV/fm3

    dNg/dy > 1100

Tave = 300 - 400 MeV (?)

PHENIX preliminary

The matter modifies jets

The matter may melt but regenerate J/y’s

The matter is hot



The matter is so hot that it emits thermal photon copiously

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


Theoretical explanation low p

Comparison to model calculations

with and without parton energy loss:

Estimation from data

  • 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!


Initial state effects (test experiment d+Au) low p

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



How about suppression for protons? low p

New

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


Jets composition as measured by STAR low p

Kirill Filimonov, QM’04


( low p pQCD x Ncoll) / background Vogelsang/CTEQ6

( pQCD x Ncoll) / (background x Ncoll)

[w/ the real suppression]

[if there were no suppression]

Binary scaling. Is it work?

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

Preliminary

pT (GeV/c)

[]measured / []background = measured/background


Theoretical explanation low p

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!


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

May be. Look at the BRAMS DATA


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