The History of BUU Codes at Gießen

Our interest in transport calculations started with a sabbatical visit of Ulrich Mosel at Michigan State University during spring/summer of 1986. During this time also the Giessen PhD student Wolfgang Bauer spent some time there, under the guidance of George Bertsch, but working for a degree at Giessen. While George had written one of the very first BUU codes Wolfgang Bauer rewrote this code and during Mosel's visit at MSU the first calculations of particle production, in this case photons, were done and later published. With Wolfgang Bauer the very first Giessen BUU code returned to Giessen.

From then on a number of very good young scientists have worked on it. Wolfgang Cassing joined the effort at this point. First, Koji Niita (Japan) rewrote again large parts of the code and implemented pion production, photon production and a good description of the nuclear ground state, Angel de Paoli and Gustavo Batko (both Argentina) used it to calculate etas and kaons produced in heavy-ion collisions and Gyuri Wolf (Hungary) did a series of important papers on dilepton production which provided some of the motivation for the construction of HADES, the dilepton spectrometer at GSI. Very early on, a parallel development to construct a manifestly covariant BUU code was started. Giessen PhD students Volker Koch and Bernhard Blaettel wrote the first such code and used it to analyse BEVALAC cata on flow and particle production (1990). Klaus Weber in his thesis (1992) did work on a covariant description of the momentum dependence of the mean field at high energies, where the Walecka model becomes too repulsive. Tomoyuki Maruyama (Japan) followed up on this and did the first numerical implementation of an explicit momentum dependence that corrects this deficiency of the Walecka model at high energies. Giessen PhD student Andreas Lang performed the first thermal analysis of heavy-ion reactions with this code; he analyzed the degree of equilibration during heavy-ion collisions and showed that full equilibration is reached on in the latest stages of a collision when the nuclear density has already decreased below its equilibrium value. Another Giessen PhD student, Stefan Teis, then did a very complete analysis of pion and eta production in heavy-ion collisions measured by the TAPS group at GSI (1997). He also analyzed the antiprotons and very-high energy pions produced in such reactions. At about this time, diploma student Alexander Hombach did the very first application of a BUU calculation to photon-induced reactions on a nucleus, analyzing the eta-production data obtained by the TAPS group at MAMI. Alexander Hombach, in his PhD thesis, did a corresponding detailed analysis of flow observables in such collisions. Teis, together with another PhD student, Martin Effenberger, rewrote parts of the code and implemented significantly more resonance excitations into the code. At roughly the same time (1998), PhD student Jochen Geiss, applied the earlier version of the code to an analysis of ultrarelativistic heavy-ion collisions, in particular to the problem of production of strangeness and charmonium in such collisions; the interest in these questions is still alive today. ...MORE TO COME

Oliver Buss during his PhD did a complete rewrite of the code and transformed it to a modular, modern FORTRAN version. Since this point we label the code by "GiBUU".