MadGraph5_aMC@NLO

No events for decay widths with implicit intermediate particles in 2.8.2

Asked by Matthew Klimek

Since upgrading to 2.8.2 from 2.7.x, processes like h > e+ e- e+ e- don't work. The width error is enormous and no events are generated. Note however that requesting this process as h > Z Z, Z > e+ e- works fine. I suspected that this had to do with the change in v2.8 regarding zero width for t-channel particles. However, setting that option to False does not solve the problem. Also, there aren't any t-channel particles in this process, so I'm not sure why that would matter.

Apologies if I'm doing something stupid, and thanks for your help. --MK

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Olivier Mattelaer
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Best Olivier Mattelaer (olivier-mattelaer) said : 		#1

Thanks a lot for noticing us of that bug.

Indeed the options was not properly propagate in the case to 1>N.
(and therefore our setting to force that options to be False for 1>N was not used).

The following patch/version should fix that issue:
https://bazaar.launchpad.net/~maddevelopers/mg5amcnlo/2.8.3.py2/revision/298

Thanks a lot,

Olivier

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Matthew Klimek (matthewdklimek) said : 		#2

Thanks Olivier Mattelaer, that solved my question.