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Parton-Hadron-String-Dynamics at NICA energies

PHSD. Parton-Hadron-String-Dynamics at NICA energies. E lena Bratkovskaya Institut für Theoretische Physik , Uni. Frankfurt Round Table Discussion IV : ‚ Searching for the mixed phase of strongly interacting matter at the Nuclotron-based Ion Collider fAcility (NICA) ‘

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Parton-Hadron-String-Dynamics at NICA energies

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  1. PHSD Parton-Hadron-String-Dynamics at NICA energies Elena Bratkovskaya Institut für Theoretische Physik, Uni. Frankfurt Round Table Discussion IV: ‚Searching for the mixed phase of strongly interacting matter at the Nuclotron-based Ion Collider fAcility (NICA)‘ 9-12 September 2009 , JINR, Dubna

  2. Our ultimate goals: • Search for the critical point The phase diagram of QCD • Study of the phase transition from hadronic to partonic matter – Quark-Gluon-Plasma NICA • Study of the in-medium properties of hadrons at high baryon density and temperature

  3. The QGP in Lattice QCD Quantum Cromo Dynamics : predicts strong increase of the energy density e at critical temperature TC ~170 MeV • Possible phase transition fromhadronic to partonic matter (quarks, gluons) at critical energy densityeC~1 GeV/fm3 Lattice QCD: energy density versus temperature Tc= 170 MeV Critical conditions - eC~1 GeV/fm3 , TC ~170 MeV -can be reached in heavy-ion experiments at bombarding energies > 5 GeV/A

  4. Quark-Gluon-Plasma ? ‚Little Bangs‘ in the Laboratory Initial State Hadronization time Au Au hadron degrees of freedom hadron degrees of freedom quarks and gluons How can we proove that an equilibrium QGP has been created in central Au+Au collisions ?!

  5. Signals of the phase transition: • Strangeness enhancement • Multi-strange particle enhancement in A+A • Charm suppression • Collective flow (v1, v2) • Thermal dileptons • Jet quenching and angular correlations • High pT suppression of hadrons • Nonstatistical event by event fluctuations and correlations • ... Experiment: measures final hadrons and leptons How to learn about physics from data? Compare with theory!

  6. Basic models for heavy-ion collisions • Statistical models: basic assumption: system is described by a (grand) canonical ensemble of non-interacting fermions and bosons in thermal and chemical equilibrium [ -: no dynamics] • Ideal hydrodynamical models: basic assumption: conservation laws + equation of state; assumption of local thermal and chemical equilibrium [ -: - simplified dynamics] • Transport models: based on transport theory of relativistic quantum many-body systems - off-shell Kadanoff-Baym equations for the Green-functions S<h(x,p) in phase-space representation. Actual solutions: Monte Carlo simulations with a large number of test-particles [+: full dynamics | -: very complicated]  Microscopic transport models provide a unique dynamical description of nonequilibrium effects in heavy-ion collisions

  7. HSD microscopic transport model - basic concept HSD – Hadron-String-Dynamics transport approach Basic concept: Generalized transport equations on the basis of the off-shell Kadanoff-Baym equations for Greens functions G<h(x,p) in phase-space representation (accounting for the first order gradient expansion of the Wigner transformed Kadanoff-Baym equations beyond the quasiparticle approximation). Actual solutions: Monte Carlo simulations with a large number of test-particles Degrees of freedom in HSD: • hadrons - baryons and mesons including excited states (resonances) • strings – excited color singlet states (qq-q) or (q-qbar) • leading quarks(q, qbar) & diquarks (q-q, qbar-qbar) HSD – a microscopic model for heavy-ion reactions: • very good description of particle production in pp, pA reactions • unique description of nuclear dynamicsfrom low (~100 MeV) to ultrarelativistic (~20 TeV) energies

  8. Hadron-string transport models versus observables NICA NICA NICA NICA Reasonable description of strangeness by HSD and UrQMD (deviations < 20%) works very well, but where do we fail ? NICA

  9. Hadron-string transport models versus observables • Strangeness signals of QGP ‚horn‘ in K+/p+ ‚step‘ in slope T Exp. data are not reproduced in terms of the hadron-string picture => evidence for nonhadronic degrees of freedom

  10. Transport description of the partonic and hadronic phase Parton-Hadron-String-Dynamics (PHSD)

  11. From hadrons to partons In order to study of the phase transition from hadronic to partonic matter – Quark-Gluon-Plasma – we need a consistent transport model with • explicit parton-parton interactions (i.e. between quarks and gluons) outside strings! • explicit phase transition from hadronic to partonic degrees of freedom • lQCD EoS for partonic phase => phase transition is always a cross-over Transport theory: off-shell Kadanoff-Baym equations for the Green-functions S<h(x,p) in phase-space representation with the partonic and hadronic phase Parton-Hadron-String-Dynamics (PHSD) W. Cassing, E. Bratkovskaya, PRC 78 (2008) 034919; arXiv:0907.5331 [nucl-th], NPA‘09; W. Cassing, EPJ ST 168 (2009) 3 QGP phase described by input from the Dynamical QuasiParticle Model (DQPM) A. Peshier, W. Cassing, PRL 94 (2005) 172301; Cassing, NPA 791 (2007) 365: NPA 793 (2007)

  12. T = 3 Tc T = 1.053 Tc T = 1.35 Tc The Dynamical QuasiParticle Model (DQPM) • Interacting quasiparticles : massive quarks and gluons with spectral functions Gluon‘s r(w): • DQPM well matches lQCD • DQPM provides mean-fields for gluons and quarks as well as effective 2-body interactions and gives transition rates for the formation of hadrons  PHSD Peshier, Cassing, PRL 94 (2005) 172301; Cassing, NPA 791 (2007) 365: NPA 793 (2007)

  13. PHSD - basic concepts Initial A+A collisions – HSD: string formation and decay to pre-hadrons Fragmentation of pre-hadrons into quarks: using the quark spectral functions from the Dynamical QuasiParticle Model (DQPM) approximation to QCD DQPM: Peshier, Cassing, PRL 94 (2005) 172301; Cassing, NPA 791 (2007) 365: NPA 793 (2007) Partonic phase: quarks and gluons (= ‚dynamical quasiparticles‘) withoff-shell spectral functions (width, mass) defined by DQPM elastic and inelastic parton-parton interactions:using the effective cross sections from the DQPM • q + qbar (flavor neutral) <=> gluon(colored) • gluon+ gluon<=> gluon(possible due to large spectral width) • q + qbar (color neutral) <=> hadron resonances Hadronization: based on DQPM - massive, off-shell quarks and gluons with broad spectralfunctions hadronize tooff-shell mesons and baryons: gluons  q + qbar;q + qbar  meson (or string); q + q +q  baryon(or string) (strings act as ‚doorway states‘ for hadrons) Hadronic phase: hadron-string interactions – off-shell HSD

  14. PHSD: hadronization E.g.time evolution of the partonic fireballat temperature 1.7 Tcwith initialized at mq=0 Consequences: • Hadronization: q+qbar or 3q or 3qbar fuse to a color neutral hadrons (or strings)which furtheron decay to hadrons in amicrocanonical fashion, i.e.obeying all conservation laws (i.e. 4-momentum conservation, flavor current conservation)in each event • Hadronization yieldsan increase in total entropy S(i.e. more hadrons in the final state than initial partons )and not a decrease as in the simple recombination model ! • Off-shell parton transport roughly leads a hydrodynamic evolution of the partonic system W. Cassing, E. Bratkovskaya, PRC 78 (2008) 034919; arXiv:0907.5331 [nucl-th], NPA‘09; W. Cassing, EPJ ST 168 (2009) 3

  15. Time-evolution of parton density Time-evolution of hadron density PHSD: Expanding fireball Expanding grid: Δz(t) = Δz0(1+a t) ! PHSD: spacial phase ‚co-existence‘ of partons and hadrons, but NO interactions between hadrons and partons (since it is a cross-over)

  16. Application to nucleus-nucleus collisions central Pb + Pb at 158 A GeV energy balance particle balance only about 40% of the converted energy goes to partons; the rest is contained in the ‚large‘ hadronic corona! Cassing & Bratkovskaya, arXiv:0907.5331 [nucl-th], NPA (2009)

  17. Partonic phase at NICA energies partonic energy fraction vs centrality and energy Dramatic decrease of partonic phase with decreasing energy and centrality Cassing & Bratkovskaya, arXiv:0907.5331 [nucl-th], NPA (2009)

  18. Proton stopping at SPS / NICA • looks not bad in comparison to NA49 data, but not sensitive to parton dynamics (PHSD = HSD)! Cassing & Bratkovskaya, arXiv:0907.5331 [nucl-th], NPA (2009)

  19. Rapidity distributions of p, K+, K- pion and kaon rapidity distributions become slightly narrower Cassing & Bratkovskaya, arXiv:0907.5331 [nucl-th], NPA (2009)

  20. PHSD: Transverse mass spectra at SPS / NICA Central Pb + Pb at SPS energies • PHSD gives harder spectra and works better than HSD at top SPS (and top NICA) energies  However, at low SPS (and low NICA) energies the effect of the partonic phase is NOT seen in rapidity distributions and mT spectra Cassing & Bratkovskaya, arXiv:0907.5331 [nucl-th], NPA (2009)

  21. Rapidity distributions of strange baryons PHSDsimilar to HSD, reasonable agreement with data Cassing & Bratkovskaya, arXiv:0907.5331 [nucl-th], NPA (2009)

  22. Rapidity distributions of (multi-)strange antibaryons strange antibaryons _ _ L+S0 multi-strange antibaryon _ X+ enhanced production of (multi-) strange anti-baryons in PHSD Cassing & Bratkovskaya, arXiv:0907.5331 [nucl-th], NPA (2009)

  23. Centrality dependence of (multi-)strange (anti-)baryons strange antibaryons _ _ L+S0 strange baryons L+S0 multi-strange baryon X-- multi-strange antibaryon _ X+ enhanced production of (multi-) strange antibaryons in PHSD Cassing & Bratkovskaya, arXiv:0907.5331 [nucl-th], NPA (2009)

  24. Number of s-bar quarks in hadronic and partonic matter Number of s-bar quarks in antibaryons for central Pb+Pb collisions at 158 A GeV from PHSD and HSD significant effect on the production of (multi-) strange antibaryons due to a slightly enhanced s-sbar pair production in the partonic phase from massive time-like gluon decay and a larger formation of antibaryons in the hadronization process! Cassing & Bratkovskaya, arXiv:0907.5331 [nucl-th], NPA (2009)

  25. What is the matter at NICA ?! The phase trajectories (r(t),e(t)) for a central cell in central Au+Au collisions: • huge energy and baryon densities are reached (e > ecrit=1 GeV/fm3) at FAIR energies (> 5 A GeV), however, the phase transition might be NOT a cross-over at FAIR or NICA! • 1st order phase transition with a critical point? • co-existance of partonic and hadronic degrees of freedom (in a mixed phase)? J. Randrup et al., CBM Physics Book; PRC75 (2007) 034902

  26. Summary • Some exp. data are not well reproduced in terms of the hadron-string picture => evidence for nonhadronic degrees of freedom • PHSDprovides a consistent description of off-shell parton dynamics in line with lattice QCD; the repulsive mean fields generate transverse flow • The Pb + Pb data at top SPS energies are rather well described within PHSD including baryon stopping, strange antibaryon enhancement and meson mT slopes (will be also seen at top NICA energies) • At low SPS / NICA energies PHSD gives practically the same results as HSD (except for strange antibaryons) when the lQCD EoS (where the phase transition is always a cross-over) is used  Isthe matter at NICA a ‚mixed phase‘ of hadrons and partons?

  27. Open problems • Is the criticalenergy/temperature provided by the lQCD calculations sufficiently accurate? • How to describe a first-order phase transition in transport ? • How to describe parton-hadron interactions in a ‚mixed‘ phase?

  28. PHSD Thanks Wolfgang Cassing Olena Linnyk Volodya Konchakovski Viatcheslav D. Toneev and the numerous experimental friends and colleagues ! HSD & PHSD Team

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