Effect of equilibrium phase transition on multiphase transport in relativistic heavy ion collisions

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Effect of equilibrium phase transition
onmultiphase transport in relativistic heavy ion
collisions

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outline

1. Introduction and motivation
2. AMPT model and the time evolution
3. Collective phase transition and its effect
4. Conclusion

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I. Introduction and motivation

• Stages of heavy ion collision and different
  theoretical approach

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• Basic ideas of Monte Carlo simulation about
  transport theory

• Transport theory describes the evolution of
  parton distribition in phase space

• transport equations are numerically solved by
  simulating the dynamical evolution of the parton
  distributions as a succession of binary
  parton-parton collisions

• The mechanics about thermalization and formation
  of QGP are studied in microscopic

• Necessity to combine transport model with phase
  transition

In heavy ion simulation, when collective
phenomenon emerge, transport isnt enought
Parton phase is in pQCD vacuum, while hadron
phase is in physical vacuum
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II. AMPT model and the time evolution

• Components of A MultiPhase Transport Model (AMPT
  v2.11)

Z.W.Lin et al. PRC 72(2005)064901
AMPT v2.11 was successful in elliptic flow and
HBT but failed to describe hadron rapidity and
transverse momentum spectra
AuAu collision at 200 AGeV, impact parameter
blt3fm, parton cross section 10mb
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• Parton and hadron time evolution in AMPT v2.11

When parton interaction cease, hadrons are
produced one by one

• The percentage of parton and hadron varies with
  time

When tlt5fm/c, parton dominate, system in
deconfined phase When tgt30fm/c, hadron dominate,
system in confined phase
Problems occur 1) some partons have
unreasonable long lifetime 2) deconfined
partons exist in confined physical vacuum
3) parton-wise hadronization but no collective
phase transition
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III. Collective phase transition and its effect

• Extract temperature from particle spectrum

Assume locally thermal equilibrium, in a thermal
transverse radial flow model, the transverse
mass distribution is
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• Collective phase transition following a
  super-cooling stage

The time evolution of parton and hadron
temperature with phase transition at t5fm/c
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• The effect of collective phase transition on
  final state distribution

1) hadron rapidity distribution
AMPT with phase transition describes data better
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2) Elliptic flow
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IV. Conclusion

• Unreasonable long lifetime of partons is found
  in transport model
• To solve the problem, a collective phase
  transition is added to the transport model AMPT
  to replace the parton-wise hadronization
• Better model and data agreement are achieved for
  the longitudinal distribution and elliptic flow
• Collective phase transition is necessary for
  transport model

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II. AMPT model and the time evolution

• Components of A MultiPhase Transport Model (AMPT
  v2.11)

• Initial conditions spatial and momentum
  distributions of minijet partons from hard
  process and strings from soft process ,strings
  are melted to be partons
• Partonic transport only two-body elastic
  scatterings are considered with
• cross section . Two partons
  will undergo scattering when the closest
• distance between them is smaller than
• Hadronization
• Hadron transport

AMPT v2.11 was successful in elliptic flow and
HBT but failed to describe hadron rapidity and
transverse momentum spectra
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• Basic ideas of Monte Carlo simulation about
  transport theory

• Semi-classically, parton density distribution in
  phase space can be described by Boltzman equation
• Boltzman equation are solved by simulating the
  interaction and evolution of partons in detail
• The mechanics about thermalization and formation
  of QGP are studied microscopic

• Necessity to combine transport model with phase
  transition

In transport model, partons hadronize one by one
with unreasonable long lifetime Parton phase is
in pQCD vacuum, while hadron phase is in physical
vacuum