From Max Klein:
 attached is a simulation of CCcross section measurements for
 polarisation = 1/2 for 250 pb-1. It shows how well and to which
 x we will be able to measure uval and dval with CC. The plots show
 the reduced cross sections: cc+ which tends to (1-y)**2 dv
 [the poor dv  looses two times: it is smaller and suppressed
 by the 1-y term] and cc- which tends to uv. the polarisation factors
 are left in such that if lambda differs from 1/2 the plots are
 still of some use.
 It is important, 
 to check which max x we can reach. My conclusion is:
 beyond 0.7-0.8 is excluded for uv and beyond 0.6 for dv.
 The d/u is so far UNKNOWN at large x since at high x the nuclear
 binding effects are important. thus CC+- IS a great method.
 yet, even the HERA-2 lumi goal is not enough. substantially
 more lumi would be better: it MAY be that d/u goes to a constant
 and not to zero for x--> 1 (an issue hotly discussed in the
 light of the high ET jets at FNAL).
  c u Max
I have made and shown this plot at the Jlab workshop ("physics
at large x") in April 2000