Central Rapidity Gaps in Events with a Leading Antiproton at CDF Mary Convery The Rockefeller University QCD calculations of hard diffractive processes, such as jet-gap-jet production rates, are hampered by the so-called gap survival probability, which is due to non-perturbative effects that suppress rapidity gap formation. Eliminating the gap survival probability experimentally would allow measurements to be compared directly to QCD calculations. This can be done by using events with multiple gaps, since if in a given event a single gap survives, additional gaps would also be expected to survive. This idea was tested in the soft diffraction sector. From a sample of single-diffractive (SD) events collected by CDF in Run I by triggering on a leading antiproton (which already have a forward rapidity gap), we measure the fraction of events with an additional gap (SDD) to be 0.246 ± 0.001(stat) ± 0.042(syst) [0.184 ± 0.001(stat) ± 0.043(syst)] at sqrt(s)=1800 [630] GeV. These results are compared with gap fractions which we previously measured in minimum-bias pbar-p collisions. The ratio of (2-gap/1-gap) to (1-gap/0-gap) fractions gives a suppression in gap rates due to non-perturbative effects of a factor of approximately 2.5. The renormalized gap-model of Goulianos predicts the fraction of SDD/SD rates to be approximately kappa = g(t)/beta(0) = 0.17 ± 0.02, where g(0) and beta(0) are the Pomeron-proton and proton-proton couplings, respectively. This prediction is consistent with our results.