In the usual factorization theorems, which give predictions only for
inclusive cross sections, there is considerable freedom in the choice of the
scheme to define the parton distribution functions. These theorems do not
directly apply to Monte-Carlo event generators, and more general factorization
theorems which give predictions for fully exclusive cross sections are needed.
It has been shown that appropriate parton distribution functions are uniquely
defined by the showering algorithm. In this paper, we present results of
calculations of the Monte-Carlo parton distribution functions in terms of the
commonly used MSbar parton distribution functions. At small x the differences
are large, which demonstrates the importance of using the correct parton
distribution functions in an event generator rather than MSbar parton
distribution functions. We present some simple approximations that enable an
understanding of the sizes of the results to be obtained.Comment: References corrected. Added referenc
