IMPROVING THE WEIZSACKER-WILLIAMS APPROXIMATION IN ELECTRON-PROTON COLLISIONS

We critically examine the validity of the Weizsacker-Williams approxim ation in electron-hadron collisions. We show that in its commonly used form it can lead to large errors, and we show how to improve it in or der to get accurate results. In particular, we present an improved for m that is valid beyond the leading logarithmic approximation in the ca se when a small-angle cut is applied to the scattered electron. Furthe rmore we include comparisons of the approximate expressions with the e xact electroproduction calculation in the case of heavy-quark producti on.