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We report the first observation of diffractively produced W bosons. In a sample of W → eν events produced in pp collisions at √ s=1.8 TeV, we find an excess of events with a forward rapidity gap, which is attributed to diffraction. The probability that this excess is consistent with non-diffractive production is 1.1 × 10 −4 (3.8σ). The relatively low fraction of W + Jet events observed within this excess implies that mainly quarks from the pomeron, which mediates diffraction, participate in W production. The diffractive to non-diffractive W production ratio is found to be R W = (1.15 ± 0.55)%.

We search for the flavor-changing neutral current decays of the top quark t --> q gamma and t --> qZ (here q represents the c and u quarks) in (p) over bar p collisions at root s = 1.8 TeV. We use a dataset (integral L dt similar to 110 pb(-1)) collected during the 1992-1995 run of the Collider Detector at Fermilab. We set 95% confidence level limits on the branching fractions B(t --> q gamma) < 3.2% and B(t --> qZ) < 33%, consistent with the standard model

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