Pythia creating massless electron/positron pair

Asked by Tim Tuschen on 2020-06-16

Dear experts,

I want to use MadEvent and Pythia to generate some events for an interacting dark matter model of the form e+ e- -> dark quark / anti dark quark. When I check the .lhe output from MadEvent only the 4 specified particles are present. When I then use Pythia to hadronize the quarks I can see that in the .hepmc file the first entries are the expected electrons and positrons but each is linked to a massless duplicate:

V -1 0 0 0 0 0 1 1 0
P 1 -11 0 0 5.1774999747831005e+00 5.1775000000000002e+00 5.1099999999999995e-04 4 0 0 -1 0
P 3 -11 0 0 5.1774999999725235e+00 5.1774999999725235e+00 0 21 0 0 -3 0
V -2 0 0 0 0 0 1 1 0
P 2 11 0 0 -5.1774999747831005e+00 5.1775000000000002e+00 5.1099999999999995e-04 4 0 0 -2 0
P 4 11 0 0 -5.1774999999725235e+00 5.1774999999725235e+00 0 21 0 0 -3 0

I couldn't find anything in the documentation as to why this happens and it also occurs when I generate electron/positron events that just use the SM and not my UFO. Is this an issue or just the way Pythia treats these kind of interactions?

Thanks in advance,
Tim

Question information

Language:
English Edit question
Status:
Answered
For:
MadGraph5_aMC@NLO Edit question
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Last query:
2020-06-16
Last reply:
2020-06-16

Hi,

I do not think that this is an issue, but you should ask Pythia author and not us.
I have no deep knowledge of Pythia.

Cheers,

Olivier

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