Observation of diffractive $W$ boson production at the Tevatron

We report the first observation of diffractively produced W bosons. In a sample of W{r_arrow}e{nu} events produced in p{bar p} collisions at {radical}(s)=1.8TeV, we find an excess of events with a forward rapidity gap, which is attributed to diffraction. The probability that this excess is consistent with nondiffractive production is 1.1{times}10{sup -4} (3.8{sigma}). 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 nondiffractive W production ratio is found to be R{sub W}=(1.15{plus_minus}0.55){percent}. {copyright} {ital 1997} {ital The American Physical Society}