Observation of DiffractiveW-Boson Production at the Fermilab Tevatron

We report the first observation of diffractively produced $W$ bosons. In a sample of $W\to e\nu$ events produced in $p\overline{p}$ collisions at $\sqrt{s}=1.8\mathrm{TeV}$, we find an excess of events with a forward rapidity gap, which is attributed to diffraction. The probability that this excess is consistent with nondiffractive production is $1.1\times {10}^{-4\mathrm{}}$ $\left(3.8\sigma \right)$. The relatively low fraction of $W+\mathrm{jet}$ 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 $R_W=(1.15\pm 0.55)\%$.