t behaviour is to keep the incoming rescattered parton as is, 
but to modify the unrescattered incoming parton so as to preserve the 
invariant mass of the system. Thereby the rapidity of the rescattering 
is modified.<br/> 
The alternative is to retain the rapidity (and mass) of the rescattered 
system when primordial <i>kT</i> is introduced. This is made at the 
expense of a modified longitudinal momentum of the incoming rescattered 
parton, so that it does not agree with the momentum it ought to have had