Probing hadronic formation times with antiprotons in p+A reactions at   AGS energies
  The production of antiprotons in $p+A$ reactions is calculated in a microscopic transport approach employing hadronic and string degrees of freedom (HSD). It is found that the abundancies of antiprotons as observed by the E910 Collaboration in $p+A$ reactions at 12.3 GeV/c as well as 17.5 GeV/c can approximately be described on the basis of primary proton-nucleon and secondary meson-baryon production channels for all targets. The transport calculations demonstrate that the antiproton rapidity distributions for heavy targets are sensitive to the $\bar{p}$ (or hadron) formation time in the nuclear medium. Within our analysis the data from the E910 Collaboration are reasonably described with a formation time of $ 0.4-0.8$ fm/c in the hadron rest frame. 
W. Cassing (Univ. Giessen), E.L. Bratkovskaya (Univ. Frankfurt), O.   Hansen (NBI Copenhagen)