Transcript STAR - JINR
Study of exited nuclear matter in AA interactions and status of NICA project – JINR heavy ions collider. Nikitin V.A. – for NICA/MPD collaboration JINR, Dubna. 1 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 3 The problems under discussion •Energy density. •Critical behavior •Parton density •Time evolution •Temperature •Number and nature of •Opacity degrees of freedom •Thermalization •Hadronization •Deconfinement, QGP •Equation of state •Collective behavior •. •. •. 4 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 5 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. 6 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. 7 8 Pseudorapidity distribution of inclusive particles in Au+Au interactions. 1 E p y ln ; y ; ln tg . 2 E p 2 9 V Estimation of central fireball energy density Naïve estimate = sqrt(s)/ V=5000 GeV/fm dz T h i Bjorken formula, 1983. s e dEt dE dEt s 2t ; dV t R A dz RA2 form d i 1 pE m , dy d ; y ln 2 p a E dEt t dEt ; Exp . value 600 GeV 2 e RA form dy dy i dEt / dy form h / mst , mt 0.7 GeV n dN / dy o form 0.35 fm / c; 5 15 GeV / fm3 t a 10 Independence of transverse energy on centrality and c.m. energy. Centrality – number of participating nucleons 11 Total charged particle multiplicity 12 Multiplicity distribution 13 14 Comparison of AA data with NN data A B b Namber of binary collision is 2 x 5=10 R AB P dN AB P N collis (b) dN pp RCP central dN central / N collis peripheral dN peripheral / N collis Namber of wounded nucleon is 2+5=7 15 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. 16 Glauber –Sitenko model Npar, Nbin calculation 17 Comparison of AA data with NN data If R = 1 here, nothing new going on 18 Enhencement of multistrage particles yield 19 20 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 21 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 z y x Anisotropic Flow • 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 22 Anisotropic flow from AGS to RHIC Picture: © UrQMD X Z b XZ – the reaction plane f atan py px d 3 1 d 2 E 3 ( 1 2v1cos RP 2v2 cos2 RP ) d p 2 pt dpt dy Isotropic DirectedFlow EllipticFlow 23 24 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-phasedominated) EOS ~ consistent with LQCD expectations for QGP hadron 25 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) 26 27 Suppression of High Transverse Momentum Hadrons by factor ~ 4 - 5 in central collisions 28 pp and peripheral AA Central AA Trigger jet Trigger jet QGP Away jet Missing away jet 29 Evidence for Parton Energy Loss in High Density Matter 30 31 Soft Sector: Hadron Yield Ratios STAR PHENIX Strangeness Enhancement Resonances 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? 32 Particle Ratios Chemical Equilibrium Temperature Statistics, grand canonical distribution and chemical potential n w(n, ) exp( )( n, ) grand canonical distrib. T d TdS pdV dn; chemical potential is energy carreing by one particle. antiparticle 0. w. 2 3q 2 B p/ p exp( ) exp( ); B 3q . T T 2( q S ) 2 K K / K exp( ) exp( ) T T 2 1 exp(( B 2 S ) ). 3 T 33 QCD Phase Diagram At RHIC: T = 177 MeV T ~ Tcritical (QCD) 34 35 Summary 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 36 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. 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 crosssection 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 Collider Ring Parameters Circumference Ion energy m GeV/u 183 2.5 – 3.5 mm mrad Collision point Beta function in CP m Rms beam size in CP m Rms angular spread in CP mrad Rms momentum spread Rms bunch length cm Peak luminosity cm-2s-1 0.5 6.0 1.2 0.001 33 51027 Ion number per beam Harmonics number Ion number per bunch 51010 20 2.5109 Rms beam emittance RF frequency RF voltage amplitude MHz kV 0.7 31.53 200 39 Nuclotron-based Ion Collider fAcility and Mixed Phase Detector NICA / MPD Water-steam transition (firstorder 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 Mixed Phase? Critical Endpoint?