Parton-Hadron-String-Dynamics at NICA energies

1
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 from hadronic to
  partonic matter (quarks, gluons) at critical
  energy density eC 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 gt 5 GeV/A
4
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 AuAu collisions ?!
5
Signals of the phase transition

• Strangeness enhancement
• Multi-strange particle enhancement in AA
• 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 Slth(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 Glth(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 dynamics from 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 lt 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 gt 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 gt phase transition
  is always a cross-over

Transport theory off-shell Kadanoff-Baym
equations for the Green-functions Slth(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 arXiv0907.5331 nucl-th, NPA09 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
The Dynamical QuasiParticle Model (DQPM)

• Interacting quasiparticles
• massive quarks and gluons
• with spectral functions

Gluons 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 AA 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) with off-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) ltgt gluon (colored)
• gluon gluon ltgt gluon (possible due to large
  spectral width)
• q qbar (color neutral) ltgt hadron resonances

Hadronization based on DQPM - massive, off-shell
quarks and gluons with broad spectral functions
hadronize to off-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 fireball at
temperature 1.7 Tc with initialized at mq0

• Consequences ?
• Hadronization qqbar or 3q or 3qbar fuse to
• a color neutral hadrons (or strings) which
  furtheron decay to hadrons in a microcanonical
  fashion, i.e. obeying all conservation laws
  (i.e. 4-momentum conservation, flavor current
  conservation) in each event
• Hadronization yields an 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 arXiv0907.5331 nucl-th, NPA09 W.
Cassing, EPJ ST 168 (2009) 3
15
PHSD Expanding fireball
Expanding grid ?z(t) ?z0(1a 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, arXiv0907.5331
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, arXiv0907.5331
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, arXiv0907.5331
nucl-th, NPA (2009)
19
Rapidity distributions of p, K, K-
? pion and kaon rapidity distributions become
slightly narrower
Cassing Bratkovskaya, arXiv0907.5331
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, arXiv0907.5331
nucl-th, NPA (2009)
21
Rapidity distributions of strange baryons
? PHSD similar to HSD, reasonable agreement with
data
Cassing Bratkovskaya, arXiv0907.5331
nucl-th, NPA (2009)
22
Rapidity distributions of (multi-)strange
antibaryons
strange antibaryons _ _ LS0
multi-strange antibaryon _ X
? enhanced production of (multi-) strange
anti-baryons in PHSD
Cassing Bratkovskaya, arXiv0907.5331
nucl-th, NPA (2009)
23
Centrality dependence of (multi-)strange
(anti-)baryons
strange antibaryons _ _ LS0
strange baryons LS0
multi-strange antibaryon _ X
multi-strange baryon X--
? enhanced production of (multi-) strange
antibaryons in PHSD
Cassing Bratkovskaya, arXiv0907.5331
nucl-th, NPA (2009)
24
Number of s-bar quarks in hadronic and partonic
matter
Number of s-bar quarks in antibaryons for central
PbPb 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, arXiv0907.5331
nucl-th, NPA (2009)
25
What is the matter at NICA ?!
The phase trajectories (r(t),e(t)) for a central
cell in central AuAu collisions

• huge energy and baryon densities are reached (e gt
  ecrit1 GeV/fm3) at FAIR energies (gt 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 gt evidence for
  nonhadronic degrees of freedom
• PHSD provides 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
• ? Is the matter at NICA a mixed phase of
  hadrons and partons?

27
Open problems

• Is the critical energy/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
Thanks
Wolfgang Cassing Olena Linnyk Volodya
Konchakovski Viatcheslav D. Toneev and the
numerous experimental friends and colleagues !
HSD PHSD Team