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6. the event files

chapter five

6.1 where the event file is stored

  • Event files hold the kinematics of the input, intermediate and output particles of each event in a specific XML format, called Les Houches format (LHE), from the name of the place where it was designed.
  • Generate a sample for the first tests:
./bin/mg5_aMC
> generate p p > e+ e-
> output test_epem
> quit
cd test_epem
printf "0\n done\n" | ./bin/generate_events
cd Events/run_01/
gunzip unweighted_events.lhe.gz

6.2 its format and content

The LHE files are divided into three main sections.

  • the <header> section contains information regarding the generation configuration, filled differently by each Monte Carlo program.
    • MG reports the whole banner, including the cross-section
  • the <init> section contains information valid for all the events to be read only once
  • the <events> contains the set of events stored in the file
  • a detailed description of the LHE file may be found here

6.3 an event example

  • the event starts and information concerning the whole event is reported
<event>
 5      1 +8.4300000e+02 9.20849300e+01 7.54677100e-03 1.29788000e-01
  • the list of particles follows
      -2 -1    0    0    0  501 -0.0000000000e+00 +0.0000000000e+00 +1.7485182150e+01 1.7485182150e+01 0.0000000000e+00 0.0000e+00 1.0000e+00
       2 -1    0    0  501    0 +0.0000000000e+00 -0.0000000000e+00 -1.2124029558e+02 1.2124029558e+02 0.0000000000e+00 0.0000e+00 -1.0000e+00
      23  2    1    2    0    0 +0.0000000000e+00 +0.0000000000e+00 -1.0375511343e+02 1.3872547773e+02 9.2084931496e+01 0.0000e+00 0.0000e+00
     -11  1    3    3    0    0 -2.1817482672e+01 -2.9064364399e+01 -9.2895879886e+00 3.7510482176e+01 0.0000000000e+00 0.0000e+00 1.0000e+00
      11  1    3    3    0    0 +2.1817482672e+01 +2.9064364399e+01 -9.4465525442e+01 1.0121499555e+02 0.0000000000e+00 0.0000e+00 -1.0000e+00
  • a set of weights follows, useful to estimate theory uncertainties
<mgrwt>
<rscale>  0 0.92084931E+02</rscale>
<asrwt>0</asrwt>
<pdfrwt beam="1">  1        2 0.18652354E-01 0.92084931E+02</pdfrwt>
<pdfrwt beam="2">  1       -2 0.26900280E-02 0.92084931E+02</pdfrwt>
<totfact> 0.12680605E+05</totfact>
</mgrwt>
  • after the weights section, the event terminates
</event>

chapter seven