Fewer events are produced than asked for
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Dear experts,
I have a problem with the production of a sample Z+jets with Z > mu+mu-.
The problem is that altough I specify to produce 50000 events, at the end I have, as output, an lhe file of 1200 events more or less. Infact in my run_01_
</mg5proccard>
<MGGenerationInfo>
# Number of Events : 1258
# Integrated weight (pb) : 1065.14731269
</MGGenerationInfo>
<mgproccard>
My proc_card is:
import model sm-no_b_mass
define p u c s d b u~ c~ s~ d~ b~ g
define j=p
generate p p > z > mu+ mu- @0
add process p p > z > mu+ mu- j @1
add process p p > z > mu+ mu- j j @2
add process p p > z > mu+ mu- j j j @3
add process p p > z > mu+ mu- j j j j @4
I'm waiting for your suggestions because I don't manage to find the problem.
Thanks a lot.
Cheers,
Lucia
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ANSWER
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Hello Lucia,
Please first see the FAQ on our wiki, https:/
"Getting significantly fewer events than you ask for usually indicates that you are trying to integrate over a divergence. E.g., if you have gluons in your process and no drjj, pj, mjj or xqcut cuts, you hit the collinear and soft divergencies of QCD. If you have implemented your own model and given some particles zero width although the Feynman rules indicate that they can decay, the you will get a divergence in any process where these particles can occur as on-shell s-channel resonances. And so on.
You can get a hint to where the problem is by looking at the Luminocity numbers for the subprocesses and integration channels. The lowest-luminocity channel is where the problem is worst. The channels are correlated with Feynman diagrams as determined by the file config_
Most probably, there is some cut missing in your run_card.
Note that when you are running multiple jet multiplicities, you need to use a matching scheme to avoid double counting and correctly account for Sudakov effects. You find more information here (again on the wiki):
https:/
In a nutshell: Set ickkw to 1 and xqcut ~ mass scale/6 or so in the run_card, in this case xqcut ~ 15 should work well.
Another possibility is that you are running in gridpack generation mode:
.true. = gridpack
in the run_card.dat. This mode is not for event generation, but for greating a gridpack that can then be used to generate large numbers of events in a GRID-type environment. Please see https:/
All the best,
Johan
