The missing events

Asked by Keping Xie

I am simulating some processes, such as mu+ mu- > b b~ b b~ at sqrt(s)=10 TeV, either with QCD=0 or not. I try to set nevents=1e6. However, the LHE events only give 66242 for QCD and 46234 for QED (QCD=0) processes. Why the events number does not match to the nevents that I set in run_card.dat? This 66242 (or 46234) corresponding the cross section that MadGraph return or just a fraction of it (i.e. cross section * 66242/1e6)?

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Keping Xie (kepingx) said :

I am attaching the tag file:
set group_subprocesses Auto
set ignore_six_quark_processes False
set low_mem_multicore_nlo_generation False
set complex_mass_scheme False
set include_lepton_initiated_processes False
set gauge unitary
set loop_optimized_output True
set loop_color_flows False
set max_npoint_for_channel 0
set default_unset_couplings 99
set max_t_for_channel 99
set zerowidth_tchannel True
set nlo_mixed_expansion True
generate mu+ mu- > b b~ b b~ QCD=0
define p = g u c d s u~ c~ d~ s~
define j = g u c d s u~ c~ d~ s~
define l+ = e+ mu+
define l- = e- mu-
define vl = ve vm vt
define vl~ = ve~ vm~ vt~
output mupmum_4b_QED

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Olivier Mattelaer (olivier-mattelaer) said :

We do have inside the code some limitation to avoid that code can run an infinite amount of time in case of issue (like non regulated singularity).
Those are for example:
- maximum number of iteration per channel
- maximum number of times a given channel is duplicated (we do that to reach high number of events while parralizing the load)
- maximum of events evaluated within the first iteration
- maximum number of weighted events written on disk
- ...

For some complex processes such limitation can limit the number of events that a given process can generate. Most of those limit can be tweak via hidden parameter of the run_card. (you can see the command "update_tofull" to put all hidden parameter in the run_card and learned about such parameter)

Those events correspond to the full cross-section.

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