[Comphep-common] pdf in CompHEP

[Yong YANG]

Dear Alexander,

Thanks for the information.  It looks like doable. it is also convenient to
use LHAPDF library to re-calcualte the pdf value for each event, given
the P_Z of two partons, and Q value.  I didn't pay enough attention to those
information,which are already printed in each event line.

Regards,
Yong



On Wed, Jul 23, 2008 at 12:51 PM, Alexander Sherstnev <
cherstn at hep.phy.cam.ac.uk> wrote:

> 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
>
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