MadGraph5_aMC@NLO

Not generating the events

Asked by Swapan Kumar Majhi

1) generate e+ e- > b u~ mu+ vm [noborn=QED]
2) generate e+ e- > b u~ mu+ vm [virt=QED]

In case 1, it generates events but not in case 2.
I do not know why. I guess first case is the loop induced process
which is finite and hence generate events.

In 2nd case, does it wait for the real process?

If so, when I generate e+ e- > b u~ mu+ vm [QED]
full QED with a 50 Gev pt cut (hard photon) then it
says poles do not cancels.
What are the reasons for these?

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Olivier Mattelaer (olivier-mattelaer) said : 		#1

syntax [noborn=] is indeed for loop-induced.
Note that we DID not check if the process is indeed loop-induced, If this is not the case, MG5aMC is likely going to return a unphysical result (as the question ask).

syntax [virt=] is for tree*loop standalone madloop code. If tree*virt does not exist, it can also return virt*virt.
Such mode is only able to evaluate the tree*loop for (a list) of momenta.
This is mainly usefull when external code want to interface with the loop provider that we do use.

 generate e+ e- > b u~ mu+ vm [QED]

If this syntax does work, then the first syntax ([noborn=]) certainly does not make sense.
Otherwise, NLO in electroweak requires dedicated care in particular for the notion of multip-particle (i.e. a pure electron in initial state does not make sense at NLO electroweak). Therefore I'm not surprised that our code detects that your syntax does not make sense. Please check the EW paper and/or the paper about electron/positron collision at NLO.

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