Measurement of Diffractive Dijet Production at the Fermilab Tevatron

We report the observation and measurement of the rate of diffractive dijet production at the Fermilab Tevatron $\overline{p}p$ collider at $\sqrt{s}=1.8\mathrm{}\mathrm{TeV}$. In events with two jets of $E_T>20\mathrm{}\mathrm{GeV}$, $1.8<\mathrm{}|\eta |<3.5\mathrm{}$, and ${\eta }_1{\eta }_2>0\mathrm{}$, we find that the diffractive to nondiffractive production ratio is $R_{\mathrm{JJ}}=[0.75\pm 0.05(\mathrm{stat})\pm 0.09(\mathrm{syst}\left)\right]\%$. By comparing this result, in combination with our measured rate for diffractive $W$ boson production reported previously, with predictions based on a hard partonic pomeron structure, we determine the pomeron gluon fraction to be $f_g=0.7\mathrm{}\pm 0.2$.