Lowest-order contribution of soft gluon rescattering for large rapidity gap events in DIS

Using a powerful PQCD technique developed by Luo, Qiu and Sterman, we derive the diffractive structure functions at the lowest order. The procedure leading to these results is straightforward. More importantly, in this approach, we find that, effectively, there are no double hard scatterings of gluons responsible for the diffractive process at lowest order. The dominant scattering process must involve a soft gluon. This soft gluon contributes to the process only by adding two colour vertex terms to the cross section without affecting the kinematic state, thus the kinematics is the same as that of the PGF process. Our approach displays the important role played by the soft gluon in LRG events exactly. (author)