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Matthias Hempel, and Jürgen Schaffner-Bielich
Institut für Theoretische Physik
J. W. Goethe-Universität, Frankfurt
44th Karpacz Winter School of Theoretical Physics
27.02.2008
A statistical model for hot hadronic matter
Motivation
Description of the model
Results for -free matter
Results for trapped ’s
Summary & outlook
Outline
A statistical model for hot hadronic matter
Motivation
Matthias Hempel
Ladek Zdroj, February 27, 2008
EoS and composition at finite T is of interest for Supernovae, cooling or accreting NS, collisions between compact stars, (heavy ion collisions) …
at present only two models available (Shen & Lattimer Swesty)
focus on matter below saturation density (crust) and construct a model that describes the liquid-gas phase transition with a grand-canonical statistical ensemble
sub-saturated matter important for e.g.:
- SN dynamics (stall of the shock front)
- cooling of NS
directly accessible by heavy ion collisions in form of multifragmentation
Motivation
present models describe the system by one representative nucleus / the ground state of the simulated cell
no thermal or chemical ensemble
“single nucleus approximation” has little influence on the EoS; but significant effect on the composition possible
composition & form of matter (one component plasma ↔ statistical ensemble) influences e.g.:
- neutrino scattering
- thermal conductivity
Matthias Hempel
Ladek Zdroj, February 27, 2008[Burrows, A.; Lattimer, J. M.; 1984ApJ...285..294B ]
Hot Hadronic Matter – Assumptions
nuclear statistical equilibrium (T ≥ 0.5 MeV)
full grand-canonical ensemble
-free
charge neutrality: ne = np
-equilibrium: e Bp
matter described by (T, nB)
trapped ’s
charge neutrality: ne = np
no -equilibrium / finite chemical potential: e Bp
described by (T, nB, Yp)
Matthias Hempel
Ladek Zdroj, February 27, 2008
nuclei (A ≥ 2)T, nB, Yp
A1, Z1
A3, Z3
A2, Z2
Matthias Hempel
Ladek Zdroj, February 27, 2008
Hot Hadronic Matter– Ingredients
p
n
n
n
a
A1, Z1
A3, Z3
A2, Z2
nuclei (A ≥ 2)
nucleons
Matthias Hempel
Ladek Zdroj, February 27, 2008
Hot Hadronic Matter– Ingredients
T, nB, Yp
nuclei (A ≥ 2)
nucleons
electrons & positrons
p
n
n
n
a
A1, Z1
A3, Z3
A2, Z2
e-
e+
Matthias Hempel
Ladek Zdroj, February 27, 2008
Hot Hadronic Matter– Ingredients
T, nB, Yp
nuclei (A ≥ 2)
nucleons
electrons & positrons
photons
p
n
n
n
a
A1, Z1
A3, Z3
A2, Z2
e-
e+
Matthias Hempel
Ladek Zdroj, February 27, 2008
Hot Hadronic Matter– Ingredients
T, nB, Yp
nuclei (A ≥ 2)
nucleons
electrons & positrons
photons
Matthias Hempel
Ladek Zdroj, February 27, 2008
Hot Hadronic Matter– Ingredients
Nuclei
if available experimental data of Audi, Wapstra and Thibault (2003): binding energies of over 2000 precisely measured nuclei
A1, Z1
A3, Z3
T, B
A2, Z2
Matthias Hempel
Ladek Zdroj, February 27, 2008
direct use of experimental data for the construction of the EoS
Nuclei
experimentally unknown nuclei: mass table generated with theoretical nuclear model
A1, Z1
A3, Z3
T, B
A2, Z2
Matthias Hempel
Ladek Zdroj, February 27, 2008
standard relativistic mean-field description
parameter-set TMA with mass number-dependent coupling constants
BCS -force pairing
axial deformations
rms(AW)~2.1 MeV
but: neglect of temperature and medium effects
[Geng, L.; Toki, H.; Meng, J.; 2005PThPh.113..785G]
Nuclei – Theoretical Nuclear Model
A1, Z1
A3, Z3
T, B
A2, Z2
Matthias Hempel
Ladek Zdroj, February 27, 2008
Maxwell-Boltzmann gas for every nucleus (Ai,Zi)
classical, non-relativistic Boltzmann description always adequate
chemical potential:
number density:
empirical formula for level density
Nuclei – Thermodynamics
A1, Z1
A3, Z3
T, B
A2, Z2
Matthias Hempel
Ladek Zdroj, February 27, 2008[Fai, G.; Randrup, J.; 1982NuclPhysA.381..557]
Nuclei – Coulomb Energies
Wigner-Seitz approximation
included as corrections to the nuclear masses:
Ai, Zi
Ri
RWS
e-
e+
e-e+
A1, Z1
p
T, B
A3, Z3
A2, Z2
e-e+
e-
e+
Matthias Hempel
Ladek Zdroj, February 27, 2008
only valid if :
but if ideal gas limit
achieved
Nucleons
free Fermi-gas at finite T (high accurate Fermi-Dirac integration routine)
n
n
n
T, B
p
Matthias Hempel
Ladek Zdroj, February 27, 2008
same relativistic mean-field description as for nuclei (at finite T)
nuclear matter properties:
[Gong, Z. et al.; 2001CoPhC.136..294G ]
Thermodynamics
finite size of baryons excluded volume principle
P, s corrected in the same manner
thermodynamic inconsistent due to neglect of derivative terms
n
n
n
A1, Z1
A3, Z3
T, B
e-e+
A2, Z2
p
e-e+
[Kouno, H.; Takagi, F.; 1989ZPhysC.45..43]Matthias Hempel
Ladek Zdroj, February 27, 2008
Results – -free – Composition
neutron drip
nB(ND) = 2x10-4 fm-³
~ nB0(ND) = 2.7x10-4 fm-³
mass fractions
Matthias Hempel
Ladek Zdroj, February 27, 2008
full T=0 calculations with explicit lattice energy reproduced (smoothed)
unexpected decreasing <A> at large density (limited mass table)
spread at transition points
average mass number <A> and standard deviation
Results – -free – Composition
Matthias Hempel
Ladek Zdroj, February 27, 2008[Rüster, S. B.; H. M.; Schaffner-Bielich, J.; 2006PhRvC..73c5804R ]
Results – -free – Composition
nuclide distribution (mass fractions)
smeared out transition from nucleus 66Ni to 86Kr
can not be reproduced by one representative nucleus
Matthias Hempel
Ladek Zdroj, February 27, 2008
Results – -free – Composition
nuclide distribution
temperature effects decrease
neutrons begin to appear
Matthias Hempel
Ladek Zdroj, February 27, 2008
Results – -free – Composition
mass fractions
Matthias Hempel
Ladek Zdroj, February 27, 2008
Results – -free – Composition
mass fractions
nuclei dissolve into , p & n at low density
Matthias Hempel
Ladek Zdroj, February 27, 2008
Results – -free – Composition
nuclide distribution
T=0 path still observable
thermal energy larger than differences in the chemical potentials of different nuclei broad distribution
Matthias Hempel
Ladek Zdroj, February 27, 2008
Results – -free – Composition
nuclide distribution
Matthias Hempel
Ladek Zdroj, February 27, 2008
transition from neutron magic number 50 to 82
broad distribution with two maxima
Results – -free – EoS
T=0 case reproduced
important benchmark up to nB ~ 10-4 fm-3
softening above ND due to free n
P and at small densities and large T generated by the electron positron plasma
Matthias Hempel
Ladek Zdroj, February 27, 2008
Results – trapped ’s – EoS
good agreement
1st order phase transition; due to limited mass table (?)
[Lattimer, J.; Swesty, F.; 1991NuclPhysA.535..331]Matthias Hempel
Ladek Zdroj, February 27, 2008
Results – trapped ’s – EoS
good agreement for low T, but bumps from shell effects
differences at large T
Matthias Hempel
Ladek Zdroj, February 27, 2008[Shen, H. et al.; 1998NuPhA.637..435S ]
Results – trapped ’s – Composition
average mass number <A>
strong shell effects
huge differences at large densities
Matthias Hempel
Ladek Zdroj, February 27, 2008
mass fractions
Matthias Hempel
Ladek Zdroj, February 27, 2008
Results – trapped ’s – Composition
nuclei and ’s only at largest densities
average neutron number <N>
Neutrino cross-sections /<N²>
Matthias Hempel
Ladek Zdroj, February 27, 2008
Results – trapped ’s – Composition
average of squared neutron number <N²>
Matthias Hempel
Ladek Zdroj, February 27, 2008
Neutrino cross-sections /<N²>
big effect coming only from the distribution
Results – trapped ’s – Composition
nuclide distribution
Matthias Hempel
Ladek Zdroj, February 27, 2008
Results – trapped ’s – Composition
nuclide distribution
almost all nuclei of the nuclear chart populated
Matthias Hempel
Ladek Zdroj, February 27, 2008
Results – trapped ’s – Composition
nuclide distribution
almost all nuclei of the nuclear chart populated
importance of statistical treatment
Matthias Hempel
Ladek Zdroj, February 27, 2008
Results – trapped ’s – Composition
Summary
Statistical model for the EoS and composition at finite T:
grand canonical ensemble consisting of an ideal gas of nuclei (vacuum masses at T=0) and nucleons (RMF)
empirical formula for level densities
Coulomb energies included in Wigner-Seitz approximation as effective masses
excluded volume corrections for baryons
Results:
T=0 results reproduced
consistent with existing EoSs, 1st order phase transition
big differences in the composition, shell effects
Matthias Hempel
Ladek Zdroj, February 27, 2008
Outlook
extension of nuclear mass table
investigate nuclear level density / temperature dependence of BE
investigate role of the excluded volume corrections
investigate Coulomb energies
inclusion of medium effects on the nuclear binding energies
Matthias Hempel
Ladek Zdroj, February 27, 2008
Outlook – Density Dependence of BE
full RMF calculation with fixed external neutron density by Thomas Bürvenich (Frankfurt, FIAS)
Matthias Hempel
Ladek Zdroj, February 27, 2008
simple quadratic behaviour (?)
extension of the Bethe-Weizsäcker mass formula
preliminary
Outlook
extension of nuclear mass table
investigate nuclear level density / temperature dependence of BE
investigate role of the excluded volume corrections
investigate Coulomb energies
inclusion of medium effects on the nuclear binding energies
study different theoretical nuclear models (other parameter sets & mass tables, Skyrme-HF)
use more realistic low density homogenous nuclear matter EoS
generate a full (nB, Yp, T) EoS table
Matthias Hempel
Ladek Zdroj, February 27, 2008