
 Timestamp:

Jan 15, 2009, 11:10:09 AM (11 years ago)
 Author:

oliver
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v19

v20


4  4  The BUU equation, which can be derived from the socalled [http://www.amazon.de/QuantumStatisticalMechanicsEquilibriumNonequilibrium/dp/020141046X/ref=sr_1_5?ie=UTF8&s=booksintlde&qid=1202470987&sr=85 KadanoffBaymequations], describes the time evolution of the Wigner transform of the realtime Green’s function. This Wigner transform represents a generalization of the classical phasespace density. We get for each particle species one such equation. All are coupled through the gain and loss terms which represent scattering processes and the mean fields being included in the Hamiltonians. 
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6   The GiBUU model includes 61 baryonic and 31 mesonic states. The necessary parameters (e.g. pole masses, life times in vacuum, branching ratios) are based on the [http://www.slac.stanford.edu/spires/find/hep/www?rawcmd=find++a+manley+and+saleski&FORMAT=WWW&SEQUENCE= Manley analysis] and the [http://pdg.lbl.gov/ PDG] compilation. The BUU equation is solved applying a testparticle ansatz in a full ensemble scheme which guarantees locality in the scattering processes of the testparticles. Resonances are explicitly propagated, [wiki:testOffshell in particular offshell]. Hence an offshell potential according to [htdocs:files/effenberger.pdf Effenberger et al.] is introduced which influences the timedevelopment of the spectral functions. The loss and gain terms include besides particle decays also two and threebody reaction channels. The lowenergy twobody reaction rates are to a large extent given by resonance excitations. Whereas at higher centerofmass energies (above 2 GeV for mesonbaryon and above 2.6 GeV baryonbaryon scattering) an enhanced version of [http://www.thep.lu.se/~torbjorn/Pythia.html Pythia] is implemented to describe the reaction processes. The Hamiltonian of the nucleon and baryonic resonances includes a momentumdependent Skyrmelike potential. For the pion, we consider a lowenergy potential based on the Deltahole model and on pionic atom phenomenology. Also Coulomb distortions are taken into account. The nuclear ground state is treated within a local ThomasFermi approximation. For this the nuclear density profiles are parametrized according to elastic electronscattering data and HartreeFock nuclearmanybody calculations. The GiBUU code is written modular in Fortran 2003 and is being developed in a multiuser environment. 
 6  The GiBUU model includes 61 baryonic and 31 mesonic states. The necessary parameters (e.g. pole masses, life times in vacuum, branching ratios) are based on the [http://www.slac.stanford.edu/spires/find/hep/www?rawcmd=find++a+manley+and+saleski&FORMAT=WWW&SEQUENCE= Manley analysis] and the [http://pdg.lbl.gov/ PDG] compilation. The BUU equation is solved applying a testparticle ansatz in a full ensemble scheme which guarantees locality in the scattering processes of the testparticles. Resonances are explicitly propagated, [wiki:testOffshell in particular offshell]. Hence an offshell potential according to [htdocs:files/effenberger.pdf Effenberger et al.] is introduced which influences the timedevelopment of the spectral functions. The loss and gain terms include besides particle decays also [wiki:Xsections two] and threebody reaction channels. The lowenergy twobody reaction rates are to a large extent given by resonance excitations. Whereas at higher centerofmass energies (above 2 GeV for mesonbaryon and above 2.6 GeV baryonbaryon scattering) an enhanced version of [http://www.thep.lu.se/~torbjorn/Pythia.html Pythia] is implemented to describe the reaction processes. The Hamiltonian of the nucleon and baryonic resonances includes a momentumdependent Skyrmelike potential. For the pion, we consider a lowenergy potential based on the Deltahole model and on pionic atom phenomenology. Also Coulomb distortions are taken into account. The nuclear ground state is treated within a local ThomasFermi approximation. For this the nuclear density profiles are parametrized according to elastic electronscattering data and HartreeFock nuclearmanybody calculations. The GiBUU code is written modular in Fortran 2003 and is being developed in a multiuser environment. 
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