Formation time of hadrons in photon induced reactions on nuclei

We present a way 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 far beyond simple Glauber theory. We show that the purely absorptive treatment of the final state interactions as usually done in simple Glauber theory might 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^+ and K^- production on C and Pb in the photon energy range 1-7 GeV.