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