MadGraph5_aMC@NLO

Error detected in "launch auto"

Asked by Zack

Hi everyone,

I am trying to launch the NLO process p p > t t~ b b~, using the 5 flavor definition p = g u d c s b u~ d~ c~ s~ b~, however I'm getting the following error that I can't seem to figure out:

Fatal error in set_tau_min
Error detected in "launch auto "
write debug file /home/zack/ttbb5flavorNLO/run_03_tag_1_debug.log
If you need help with this issue please contact us on https://answers.launchpad.net/madgraph5
aMCatNLOError : Some tests failed, run cannot continue.
Please check that widths of final state particles (e.g. top) have been set to 0 in the param_card.dat.

I have checked and all the correct particles have been set to 0. This process works fine with LO accuracy, but when I switch to NLO this happens. Does anyone have any ideas why it is doing this?

Thank you in advance!

Question information

Language:
English Edit question
Status:
Solved
For:
MadGraph5_aMC@NLO Edit question
Assignee:
marco zaro Edit question
Solved by:
marco zaro
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Revision history for this message
Best marco zaro (marco-zaro) said : 		#1

Hi Zack,
you cannot compute this process in the 5fs because in this scheme you have uncanceled singularities:
think of t t~ > b b~ g, it can come from t t~ > b b~ + gluon radiation or from t t~ g g + g > b b~ splitting.
If you want to simulate this process, you have to use the 4fs, or, alternatively, to compute
t t~ j j (with j including the b) and at the analysis level check that you have b's in the final state. This last case however is highly inefficient.
Please let me know if you need more help.

Cheers,

Marco

Revision history for this message
Zack (khfrekek) said : 		#2

Thanks marco zaro, that solved my question.

Revision history for this message
Zack (khfrekek) said : 		#3

Thanks Marco! I ended up just switching to the 4fs and it worked just fine. Thank you so much for your help!