The Tensor Structure Function $b_2(x,Q^2)$ of the Deuteron at Small x

Abstract

The dependence of the diffractive nuclear shadowing and the nuclear pion excess effect on the deuteron spin alignment leads to a substantial tensor polarisation of sea partons in the deuteron. The corresponding tensor structure function $b_2(x,Q^2)$ rises towards small $x$, and we predict the about one percent tensor asymmetry $A_2(x,Q^2) =b_2(x,Q^2)/F_{2D}(x,Q^2)$. We calculate the shadowing of the gluon distribution in the deuteron for two different pomeron gluon-distributions. For a hard gluon dominated $\Pom$-structure function, as advocated by H1, we find large gluon shadowing, which appears to be in conflict with the DGLAP analysis of nuclear SF's.