Central pseudorapidity gaps in events with a leading antiproton at the Fermilab Tevatron p-barp collider

We report a measurement of the fraction of events with a large pseudorapidity gap Δη within the pseudorapidity region available to the proton dissociation products X in p-bar+p→p-bar+X. For a final state p-bar of fractional momentum loss ξp and 4-momentum transfer squared tp within 0.06<ξp<0.09 and |tp|<1.0 [0.2] GeV2 at √(s)=1800 [630] GeV, the fraction of events with Δη>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(bar sign)p collisions and with theoretical expectations