Central Pseudorapidity Gaps in Events with a Leading Antiproton at the Fermilab Tevatron p̅p Collider

We report a measurement of the fraction of events with a large pseudorapiditygap Deltaeta within the pseudorapidityregion available to the proton dissociation products X in (p) overbar +p-->(p) overbar +X. For a final state (p) overbar of fractional momentum loss xi((p) overbar) and 4- momentum transfersquared t((p) overbar) within 0.06 3 is found to be 0.246+/-0.001 ( stat)+/-0.042 (syst) [0.184+/-0.001 ( stat)+/-0.043 (syst)]. Our results are compared with gap fractions measured in minimum bias (p) overbarp collisions and with theoretical expectations.