768 research outputs found
Off-shell effects on particle production
We investigate the observable effects of off-shell propagation of nucleons in
heavy-ion collisions at SIS energies. Within a semi-classical BUU transport
model we find a strong enhancement of subthreshold particle production when
off-shell nucleons are propagated.Comment: 11 pages, 3 figure
Hadron formation in high energy photonuclear reactions
We present a new method to account for coherence length effects in a
semi-classical transport model. This allows us to describe photo- and
electroproduction at large nuclei (A>12) and high energies using a realistic
coupled channel description of the final state interactions that goes beyond
simple Glauber theory. We show that the purely absorptive treatment of the
final state interactions can lead to wrong estimates of color transparency and
formation time effects in particle production. As an example, we discuss
exclusive rho^0 photoproduction on Pb at a photon energy of 7 GeV as well as
K^+ production in the photon energy range 1-7 GeV.Comment: 14 pages, 6 figures, version published in Phys. Rev.
In-medium broadening of nucleon resonances
We analyze the effects of an in-medium broadening of nucleon resonances on
the exclusive photoproduction of mesons on nuclei as well as on the total
photoabsorption cross sections in a transport calculation. We show that the
resonance widths observed in semi-inclusive photoproduction on nuclei are
insensitive to an in-medium broadening of nucleon resonances. This is due to a
simple effect: the sizeable width of the nuclear surface and Fermi motion.Comment: 4 pages, 3 figures, minor changes in the tex
Photoproduction of mesons in nuclei at GeV energies
In a transport model that combines initial state interactions of the photon
with final state interactions of the produced particles we present a
calculation of inclusive photoproduction of mesons in nuclei in the energy
range from 1 to 7 GeV. We give predictions for the photoproduction cross
sections of pions, etas, kaons, antikaons, and invariant mass
spectra in ^{12}C and ^{208}Pb. The effects of nuclear shadowing and final
state interaction of the produced particles are discussed in detail.Comment: Text added in summary in general reliability of the method,
references updated. Phys. Rev. C (2000) in pres
Transport Theoretical Approach to the Nucleon Spectral Function in Nuclear Matter
The nucleon spectral function in infinite nuclear matter is calculated in a
quantum transport theoretical approach. Exploiting the known relation between
collision rates and correlation functions the spectral function is derived
self-consistently. By re-inserting the spectral functions into the collision
integrals the description of hard processes from the high-momentum components
of wave functions and interactions is improved iteratively until convergence is
achieved. The momentum and energy distributions and the nuclear matter
occupation probabilities are in very good agreement with the results obtained
from many-body theory.Comment: minor changes in the text, additional curves in fig.
e^+e^- Pair Production from A Reactions
We present a calculation of e^+e^- production in reactions at MAMI
and TJNAF energies within a semi-classical BUU transport model. Dilepton
invariant mass spectra for C, Ca and Pb are calculated
at 0.8, 1.5 and 2.2 GeV. We focus on observable effects of medium modifications
of the and mesons. The in-medium widths of these mesons are
taken into account in a dynamical, consistent way. We discuss the transport
theoretical treatment of broad resonances.Comment: 42 pages including 16 figure
- …