nikitin v.a. – for nica/mpd collaboration jinr, dubna

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Study of exited nuclear matter

in AA interactionsand

status of NICA project – JINR heavy ions collider.

Nikitin V.A.

– for NICA/MPD collaboration

JINR, Dubna.

Summary. • Intensive study of AA collisions in energy domain sqrt(s)>20 A

GeV have showed existence of hadronic matter with unusual properties (e.g. strong suppression of high p_t partons). But long expected phase transitions were not observed yet. Recently declared wide programs of continuation the phase transitions search make emphasis on precision study in energy domain 2 – 10 A GeV were compressed matter with high baryon density is expected to be created. For this purpose JINR planes to construct facility NICA/MPD – “Nuclotron-based Ion Collider fAcility and Mixed Phase Detector”. It will accelerate all nuclei up to U to top energy sqrt(s)=10 A GeV. The main physical setup MPD includes set of instrumentation to detect central U+U collisions with multiplicity 600 charged particles in 4π geometry. Option with polarized deuteron beam is also anticipated. 2

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The problems under discussion

•Energy density.

•Parton density

•Temperature

•Opacity

•Thermalization

•Deconfinement, QGP

•Collective behavior

•Critical behavior

•Time evolution

•Number and nature of

degrees of freedom

•Hadronization

•Equation of state

•.

•.

•.

5Chemical freeze-out (Tch ~ Tc): inelastic scattering ceases

Kinetic freeze-out (Tfo Tch): elastic scattering ceases

hard (high-pT) probes

soft physics regime

QGP: thermalized system with partonic degrees of freedom

System Evolution of a Heavy-Ion Collision

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What Have We Learned at RHIC So Far?1. Large energy densities (dn/dh, dET/dh) e 5 GeV/fm3

30 - 100 x nuclear density.

2. Large produced particle multiplicities.

dnch/dy (y=0) = 670, Ntotal ~ 7500,

> 15,000 q +q in final state.

3. Collective phenomena:

Large elliptic flow. Extreme early onset of pressure gradients & high energy densities

Hydrodynamic & requires quark-gluon equation of state.4. Constituent quark degrees of freedom.

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What Have We Learned at RHIC So Far?5. Chemical” equilibration. Particles yields represent equilibrium abundances and universal hadronization temperature.

Chemical Freezeout Conditions. T = 177 MeV, = 29 MeV.

6. Thermal equilibration obtained from particle spectra: thermal freezeout + large transverse flow. T = 100-110 MeV, = 0.5 – 0.6.

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Pseudorapidity distribution of inclusive particles in Au+Au interactions.

1ln ; ; ln .

2 2

E py y tg

E p

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Estimation of central fireball energy density Naïve estimate

This estimate is not adequate to physics to be studied.

dz

2 2

2

3

;

1ln , ;

2

; . 600

// , 0.7

/

0.35 / ; 5 15 /

t t t

A A form

t t

A form

tform t t

form

dE dE dE

dV R dz R d

p Ey dy d

p E

dE dEExp value GeV

R dy dy

dE dyh m m GeV

dN dy

fm c GeV fm

Bjorken formula, 1983.

V

= sqrt(s)/ V=5000 GeV/fm

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Independence of transverse energy on centrality and c.m. energy.

Centrality – number of participating nucleons

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Total charged particle multiplicity

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Multiplicity distribution

1414

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Comparison of AA data with NN data

A B

b

peripheralcollis

peripheral

centralcollis

central

CP

Pppcollis

PAB

AB

NdNNdN

R

dNbNdN

R

//

)(

Namber of binary collision is 2 x 5=10

Namber of wounded nucleon is 2+5=7

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High cross section phenomena (soft processes) scales with the number of participants. Low cross section phenomena (hard processes) scales with the number of binary collisions.

pp: npart = 2; nbin = 1

AA: npart = 8; nbin = 16

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Glauber –Sitenko model Npar, Nbin calculation

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Comparison of AA data with NN data

If R = 1 here, nothing new going on

Enhencement of multistrage particles yield

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A Definition of the Quark-Gluon Plasma

QGP a (locally) thermally equilibrated state of matter in which quarks and gluons are deconfined from hadrons, so that color degrees of freedom become manifest over nuclear, rather than merely nucleonic, volumes.

Not required: non-interacting quarks and gluons 1st- or 2nd-order phase transition evidence of chiral symmetry restoration

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Anisotropic Flow

x

yz

• The overlap region in peripheral collisions is not symmetric in coordinate space

• Interactions among constituents generatesa pressure gradient which transforms the initial spatial anisotropy into the observed momentum anisotropy

• Perform a Fourier decomposition of the momentum space particle distributions in the x-y plane

– v2 is the 2nd harmonic Fourier coefficient of

the distribution of particles with respect to the reaction plane

Elliptic flow of central fireball matter

px

py

Peripheral Collisions

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Anisotropic flow from AGS to RHIC

X

Z b

XZ – the reaction plane

Picture: © UrQMD

)

FlowElliptic

2cos2

FlowDirected

cos2 Isotropic

1 ( 2

121

2

3

3

RPRPtt

vvdydpp

d

pd

dE

x

y

p

patan

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Soft Sector: Evidence for Thermalization and EOS Soft Sector: Evidence for Thermalization and EOS

Systematic m-dependence of v2(pT) suggests common transverse vel. field

mT spectra and v2 systematics for mid-central collisions at low pT are well (~20-30% level) described by hydro expansion of ideal relativistic fluid

Hydro success suggests early thermalization, very short mean free path

Best agreement with v2 and spectra for therm < 1 fm/c and soft (mixed-phase- dominated) EOS ~ consistent with LQCD expectations for QGP hadron

Hydro calculations: Kolb, Heinz and Huovinen

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The flow is established at the quark level. It is predicted to be simple

when pT → pT / n , v2 → v2 / n , n = (2, 3 quarks)

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Suppression of High Transverse Momentum Hadrons by factor ~ 4 - 5 in central collisions

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Trigger jet

Away jet

pp and peripheral AA

Trigger jet

Missing away jet

Central AA

QGP

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Evidence for Parton Energy Loss in High Density Matter

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Soft Sector: Hadron Yield RatiosSoft Sector: Hadron Yield Ratios

Strangeness Enhancement Resonances

STARPHENIX

pT-integrated yield ratios in central Au+Au collisions consistent with Grand Canonical stat. distribution @ Tch = (160 ± 10) MeV, B 25 MeV, across u, d and s sectors.

Inferred Tch consistent with Tcrit (LQCD) T0 >Tcrit .

Does result point to thermodynamic and chemical equilibration, and not just phase-space dominance?

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Particle Ratios Chemical Equilibrium Temperature Statistics, grand canonical distribution and chemical potential

( , ) exp( ) ( , ) .

;

.

0.

.

2 32/ exp( ) exp( ); 3 .

2( )2/ exp( ) exp( )

e

antiparticle

qBB q

q SK

nw n n grand canonical distrib

Td TdS pdV dn chemical potential is energy

carreing by one particle

w

p pT T

K KT T

2 1

xp(( 2 ) ).3 B S T

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QCD Phase Diagram

At RHIC:

T = 177 MeV

T ~ Tcritical (QCD)

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Summary on QGP SearchSummary on QGP Search

All indications are that a qualitatively new form of matter is being produced in central AuAu collisions at RHIC

1) The extended reach in energy density at RHIC appears to reach simplifying conditions in central collisions -- ~ideal fluid expansion; approx. local thermal equilibrium.

2) The Extended reach in pT at RHIC gives probes for behavior inaccessible at lower energies – jet quenching; ~constituent quark scaling.

But: In the absence of a direct signal of deconfinement revealed by experiment alone, a QGP discovery claim must rest on the comparison with a theoretical framework. In this circumstance, further work to establish clear predictive power and provide quantitative assessments of theoretical uncertainties is necessary for the present appealing picture to survive as a lasting one.

In order to rely on theory for compelling QGP discovery claim, we need: greater coherence; fewer adjusted parameters; quantitative

estimates of theoretical uncertainties

NNuclotron-based uclotron-based IIon on CCollider follider fAAcility and cility and MMixed ixed PPhase hase DDetectoretector

«« NICA NICA / / MPDMPD » »

Development of the JINR basic facility for generation of intense heavy ion and polarized nuclear beams aimed at

searching for the mixed phase of nuclear matter and

investigation of polarization phenomena at the collision

energies up to sNN = 9 GeV

MAIN RESEARCH GOALS:

•Investigation of the mixed phase formation problem in strongly interacted nuclear matter at extremely high nuclear densities

• Investigation of polarization phenomena in few-body nucleon systems.

•Development of theoretical models of the processes and theoretical support of the experiments.

• Development of the Nuclotron as the basis for study of relativistic nuclear collisions over atomic mass range A = 1-238.

•Preparation of the project of the nuclear collider and multipurpose particle detector at heavy ion colliding beams (NICA/MPD) and staged realization.

• Experiments at the Nuclotron nuclear and polarized deuteron beams.

The existing Nuclotron facility •The Nuclotron was built for five years (1987-1992), the main equipment of its magnetic system, and many other systems as well, was fabricated by the JINR central and the LHE workshops without having recourse to specialized industry. The Nuclotron ring of 251.5 m in perimeter is installed in the tunnel with a cross-section of 2.5m x 3 m that was a part of the Synchrophasotron infrastructure

•Structural magnets power supply upgrade. • Beam extraction improvement of the beam pipe pumping system. •RF system. • Beam diagnostic and control system. • RF system.

•Beam transfer line from the Nuclotron ring to the main experimental area;• Cryogenic supply system;• Ion source development;• Booster magnets R&D

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Circumference m 183Ion energy GeV/u 2.5 – 3.5

Rms beam emittance mm mrad

0.7

Collision pointBeta function in CP m 0.5Rms beam size in CP m 6.0Rms angular spread in CP mrad 1.2Rms momentum spread 0.001Rms bunch length cm 33Peak luminosity cm-2s-1 51027

Ion number per beam 51010

Harmonics number 20Ion number per bunch 2.5109

RF frequency MHz 31.53RF voltage amplitude kV 200

Collider Ring Parameters

PHASE DIAGRAMS

Water-steam transition (first-order transition with the latent heat) ends a critical point (second order). No difference between steam and water above the critical point.

Quark-hadron deconfinement phase transition manifests a similar structure. There is a crossover above the critical point

NNuclotron-based uclotron-based IIon on CCollider follider fAAcility and cility and MMixed ixed PPhase hase DDetectoretector

NICANICA / / MPDMPD

Mixed Phase? Critical Endpoint?

NICA