Nikitin V.A. – for NICA/MPD collaboration JINR, Dubna.

1. 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.

2. 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.

3. Problems to be addressed

4. The problems under discussion • Critical behavior • Time evolution • Number and nature of degrees of freedom • Hadronization • Equation of state • . • . • . • Energy density. • Parton density • Temperature • Opacity • Thermalization • Deconfinement, QGP • Collective behavior

5. System Evolution of a Heavy-Ion Collision QGP: thermalized system with partonic degrees of freedom soft physics regime hard (high-pT) probes Chemical freeze-out (Tch ~ Tc): inelastic scattering ceases Kinetic freeze-out (Tfo Tch): elastic scattering ceases

6. 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.

7. What Have We Learned at RHIC So Far? 5. Chemical” equilibration. Particles yields represent equilibrium abundances anduniversal 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.

8. Fireball energy density

9. Pseudorapidity distribution of inclusive particles in Au+Au interactions.

10. This estimate is not adequate to physics to be studied. V Bjorken formula, 1983. dz Estimation of central fireball energy density Naïve estimate  = sqrt(s)/ V=5000 GeV/fm

11. Independence of transverse energy on centrality and c.m. energy. Centrality – number of participating nucleons

12. Total charged particle multiplicity

13. Multiplicity distribution

14. AA data versus NN data

15. A B b Comparison of AA data with NN data Namber of binary collision is 2 x 5=10 Namber of wounded nucleon is 2+5=7

16. pp: npart = 2; nbin = 1 AA: npart = 8; nbin = 16 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.

17. Glauber –Sitenko model Npar, Nbin calculation

18. Comparison of AA data with NN data If R = 1 here, nothing new going on

19. Enhencement of multistrage particles yield

20. Collective phenomena and QGP search

21. 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

22. z y x Anisotropic Flow py px Elliptic flow of central fireball matter Peripheral Collisions • The overlap region in peripheral collisions is not symmetric in coordinate space • Interactions among constituents generates • a 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

23. p f = y atan p x Anisotropic flow from AGS to RHIC

25. Soft Sector: Evidence for Thermalization and EOS Hydro calculations: Kolb, Heinz and Huovinen • 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

26. 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)

27. Parton absorption and jet quenching

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

29. pp and peripheral AA Central AA Trigger jet Trigger jet QGP Away jet Missing away jet

30. Evidence for Parton Energy Loss in High Density Matter

31. Thermodynamic properties

32. Soft Sector: Hadron Yield Ratios Strangeness Enhancement Resonances STAR PHENIX • 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?

33. Particle Ratios  Chemical Equilibrium  TemperatureStatistics, grand canonical distribution and chemical potential

34. At RHIC: T = 177 MeV T ~ Tcritical (QCD) QCD Phase Diagram

36. Summary on QGP Search • All indications are that a qualitatively new form of matter is being • produced in central AuAu collisions at RHIC • The extended reach in energy density at RHIC appears to reach simplifying conditions in central collisions -- ~ideal fluid expansion; approx. local thermal equilibrium. • 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

37. Nuclotron-based Ion Collider fAcility and Mixed Phase Detector «NICA / MPD » 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.

38. 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

39. Collider Ring Parameters

40. Nuclotron-based Ion Collider fAcility and Mixed Phase Detector NICA / MPD 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. PHASE DIAGRAMS Quark-hadron deconfinement phase transition manifests a similar structure. There is a crossover above the critical point

41. Mixed Phase? Critical Endpoint? NICA