Absence of shadowing in Drell-Yan production at finite transverse momentum exchange

Abstract

Within a perturbative scalar QED model recently considered by Brodsky et al., we study how leading-twist Coulomb rescatterings affect the Drell-Yan cross section at small x = x_{target}, and compare to the case of deep inelastic scattering at small x_{B}. We show that in the range where the transverse momentum transferred to the target is large compared to its minimal value $\sim \morder{x}$, Coulomb rescatterings affect the DIS cross section but not the Drell-Yan production rate. This illustrates that the leading-twist parton distribution functions become non-universal when cross sections which are differential in target-related particles are considered.

Figures (5)

• Figure 1: Forward $\gamma^* T \to \gamma^* T$ amplitude in the DIS model of Ref. bhmps.
• Figure 2: Single gluon exchange DIS amplitude in scalar QED.
• Figure 3: Forward amplitude of order $e^2 g^8$ for the Drell-Yan process. Only one diagram is shown.
• Figure 4: Diagrams contributing dominantly to the two-gluon exchange DY amplitude in Feynman gauge and in the small $x$ limit. Crossed diagrams, obtained by permuting the lower vertices, are included.
• Figure 5: A diagram (together with the contribution from the crossed one) for the two-gluon exchange DY amplitude which vanishes in the small $x$ limit.