Diffractive Dijet Production at $\sqrt{\mathit{s}}=630\mathrm{}$ and 1800 GeV at the Fermilab Tevatron

We report a measurement of the diffractive structure function $F_{\mathrm{jj}}^D$ of the antiproton obtained from a study of dijet events produced in association with a leading antiproton in $\overline{p}p$ collisions at $\sqrt{s}=630\mathrm{}\mathrm{GeV}$ at the Fermilab Tevatron. The ratio of $F_{\mathrm{jj}}^D$ at $\sqrt{s}=630\mathrm{}\mathrm{GeV}$ to $F_{\mathrm{jj}}^D$ obtained from a similar measurement at $\sqrt{s}=1800\mathrm{}\mathrm{GeV}$ is compared with expectations from QCD factorization and other theoretical predictions. We also report a measurement of the $\xi$ ( $x$-Pomeron) and $\beta$ ( $x$ of parton in Pomeron) dependence of $F_{\mathrm{jj}}^D$ at $\sqrt{s}=1800\mathrm{}\mathrm{GeV}$. In the region $0.035<\mathrm{}\xi <0.095\mathrm{}$, $|t|<1\mathrm{}{\mathrm{GeV}}^2$, and $\beta <0.5\mathrm{}$, $F_{\mathrm{jj}}^D(\beta ,\xi )$ is found to be of the form ${\beta }^{-1.0\mathrm{}\pm 0.1}{\xi }^{-0.9\mathrm{}\pm 0.1}$, which obeys $\beta -\xi$ factorization.