Scaling in ${\gamma }^{\ast }p$ total cross sections and the generalized vector dominance/color dipole picture

Abstract

The scaling in ${\sigma }_{{\gamma }^{\ast }p}$ cross sections (for $Q^2/W^2<<1$) in terms of the scaling variable $\eta =(Q^2+m_0^2)/{\Lambda }^2(W^2)$ is interpreted in the generalized vector dominance/color-dipole picture (GVD/CDP). The quantity ${\Lambda }^2(W^2)$ is identified as the average gluon transverse momentum absorbed by the $q\bar{q}$ state, $<{\vec{l}}^2>=(1/6){\Lambda }^2(W^2)$. At any $Q^2$, for $W^2\to \infty$,the cross sections for virtual and real photons became universal, ${\sigma }_{{\gamma }^{\ast }p}(W^2,Q^2)/{\sigma }_{\gamma p}(W^2)\to 1$.

Comments: 6 pages, Latex using psfig, 3 figures. Presented at DIS 2001, Bologna, Italy, Apil 27 to May 1, 2001