Diffractive Dissociation in $ep$ Deep Inelastic Scattering

The deep inelastic diffractive cross section, $d \sigma^D_{\gamma* p\to XN}/dM_x$ , has been measured in the mass range $M_x \leq$15 GeV for $\gamma^* p$ center of mass energies 60 < W < 200 GeV and photon virtualities $Q^2$ = 7 to 140 $GeV^2$. For fixed $Q^2$ and $M_x$, the diffractive cross section is found to rise rapidly with W. Parameterizing the $W$ dependence by the form $d\sigma^D_{\gamma* \to XN}$/$dM_x \propto (W^2)$ $^{2\overline{\alpha_P} -2}$ the data yielded for the i-averaged Pomeron trajectory a value of $\overline{\alpha_P}$ = 1.135 ± 0.008(stat)$^{+0.011}_{-0.030}$(syst). This value for the Pomeron trajectory is larger than $\overline{\alpha_P}$ extracted from soft interactions. The IV dependence of the diffractive cross section measured in this analysis is found to be the same as that of the total cross section for scattering of virtual photons on protons. From the measured diffractive cross section the diffractive structure function of the proton $F^{d(3)}_2$ $(\beta$,$x_P$, $Q^2$) has been determined. We find the data to be consistent with the assumption that the diffractive structure function $F^{D(3)}_2$ factorizes according to $x_P$ $F^{D(3)}_2$($x_P$, $\beta$, $Q^2$) = ($x_0$/$x_P$)$^nF^{P}_2$ ($\beta$,$Q^2$). They are also consistent with QCD based models which incorporate factorization breaking. The rise of $X_P$ $F^{D(3)}_2$ with decreasing $x_P$ and the weak dependence of $F^P_2$ on $Q^2$ suggest a substantial contribution from partonic interactions