[Comphep-common] pdf in CompHEP

[Alexander Sherstnev]

Dear Yong,

x1 and x2 can be easily calculated from current data in event files.
P_Z components of the initial particles are the 1st and 2nd column in
the file.

pdf values are available in sqme.c The file is generated automatically
by s_comphep.exe and located in results:
Here is the peace of code:
  if(!strfun_calc)
  { strfun_calc=1;
    q=qcd_Scale_chep();
    if(ans0) xstr0=strfun_(0,xbjo[0],xbjo[1],q);
    if(ans1) xstr1=strfun_(1,xbjo[0],xbjo[1],q);
  }

In fact strfun_ returns pdf1*pdf2, since CompHEP has got an
implemented approach with  non-factorized PDF (we call it hash-model).
If you use the standard pdf:
strfun_(1,xbjo[0],xbjo[1],q) = 0
strfun_(0,xbjo[0],xbjo[1],q) = pdf (xbjo[0], q) * pdf (xbjo[1], q)

If you need you can add the number to the old format file in
src/num/evnt_format1.c, the routine write_event_frmt1(...)
It is quite easy to get how to modify it.

With best regards,
-- 
Dr. Alexander Sherstnev,
Cavenidish Laboratory, University of Cambridge,
and SINP, Moscow State University
http://www.hep.phy.cam.ac.uk/people/sherstnev.html