Abstract

The cross section for deep inelastic lepton-proton scattering (DIS) `p ! `0X includes a diractive deep inelastic (DDIS) contribution `p ! `0 p0X, in which the proton remains intact with a large longitudinal momentum fraction xF greater than 0.9and small transverse momentum. The DDIS events, which can be identified with Pomeron exchange in the t-channel, accountfor approximately 10% of all of the DIS events. Thus, when one measures DIS, one automatically includes the leading-twist Bjorken-scaling DDIS events as a contribution to the DIS cross section, whether or not the final-state proton p0 is detected. In such events, the missing momentum fraction xp0  0:9 carried by the final-state proton p0 in the DDIS events could be misidentified with the light-front momentum fraction carried by sea quarks or gluons in the protons’ Fock structure. As we shall show in this article, the underlying QCD Pomeron-exchange amplitude which produces the DDIS events does not obey the operator product expansion nor satisfy momentum sum rules. Thus we conclude that the quark and gluon distributions measured in DIS experiments will be misidentified, unless the measurements explicitly exclude the DDIS events and that a correct determination of the parton distribution functions (PDFs) derived from the DIS data requires the explicit subtraction of the DDIS contribution from the fullDIS cross section