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[Comphep-common] Polarization of outgoing particles

[Comphep-common] Polarization of outgoing particles

Bertrand Martin martindl at cern.ch
Tue Oct 2 13:06:24 MSK 2012


Dear CompHEP experts,

I found a statement on http://comphep.sinp.msu.ru/overview saying:
"The present version does not take into account separate polarization  
states of particles".

I just wanted to confirm this applies to 4.5.1, and that when  
generating LHE event files to feed an external generator like Pythia8,  
no polarization information is transmitted.
(in case we have taus in the final state)

I tried to understand the event format, for instance:

<event>
5 1  1.0000000000E+00  7.4514146263E+02  1.0269608349E-01   
7.8125000000E-03
-1 -1 0 0 0 500  0.0000000000E+00  0.0000000000E+00  8.3714105528E+02   
8.3714105528E+02  0.0000000000E+00 0.0 9.0
1 -1 0 0 500 0  0.0000000000E+00  0.0000000000E+00 -6.4488184958E+02   
6.4488184958E+02  0.0000000000E+00 0.0 9.0
22 1 1 2 0 0  2.1169902315E+02 -2.5158536501E+02  5.2552949806E+02   
6.1991364368E+02  0.0000000000E+00 0.0 9.0
11 1 1 2 0 0  2.3404064522E+02  2.1465686930E+01 -2.6766260455E+02   
3.5620088322E+02  5.1100000000E-04 0.0 9.0
-11 1 1 2 0 0 -4.4573966836E+02  2.3011967808E+02 -6.5607687804E+01   
5.0590837796E+02  5.1100000000E-04 0.0 9.0
</event>

The code which dumps event to file (src/num/evnt_format_lhaef.c) reads:
[...]
      if (2 == nin_) {
        fprintf (events_, "%i 1 1 2 %i %i %17.10E %17.10E %17.10E  
%17.10E %17.10E 0.0 9.0\n",
        id, col[j][0], col[j][1], pvect[k + 1], pvect[k + 2], pvect[k  
+ 3], pvect[k], m);
      }
[...]

And I'm not sure the spin information is there.

Thanks a lot for your help.
Bertrand



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