aussian distributions in <i>p_x</i> and 
<i>p_y</i> separately. The widths of these distributions are chosen
to be dependent on the hard scale of the central process and on the mass 
of the whole subsystem defined by the two initiators:
<br/><i>
sigma = (sigma_soft * Q_half + sigma_hard * Q) / (Q_half + Q) 
  * m / (m_half + m)  
</i><br/>
Here <i>Q</i> is the hard-process renormalization scale for the 
hardest process and the <i>pT</i> scale for subsequent multiparton
interactions, <i>m</i> the mass of the