MadGraph5_aMC@NLO

how to keep only final particles

Asked by Piero Viscone

Dear all,
I am generating ttbar semileptonic events with madgraph+madspin

At the end, I found that not only the W's decay products are present, but also the W's themself.

In other words, what I see in LHEs is:

j (incoming particle)
j (incoming particle)
b
w+
ell+
vl
b~
w-
q
q~

and I want to remove the Ws.
How should I change the cards to don't save them?

------------------------------------------------------
My proc_card is:

generate p p > t t~

------------------------------------------------------
my madspin_card is:

decay t > b w+, w+ > ell+ vl
decay t~ > b~ w-, w- > q q~

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Revision history for this message
Piero Viscone (pviscone) said : 		#1

I am sorry, I just realized now that this problem is related to CMSSW and not madgraph, mark the question as invalid.
I apologize

Revision history for this message
Olivier Mattelaer (olivier-mattelaer) said : 		#2

I will answer the question anyway since we indeed wrote such W (I'm actually surprised that you do not have the top as well).
Such answer can always be interesting for others.

We do not have a mode for that in the run_card, especially since in this case, those events are not written by MadEvent but by madspin. So the only option is to hack the code and to remove the lines
            else:
                particle_line=self.get_particle_line(self.resonance[part])
line 186 of file MadSpin/decay.py

Note that if you do remove those lines, you should not use those events for parton-shower since
1) the color information of the events might not be correct any more (then the parton-shower will crash anyway)
2) the parton-shower will lack information for properly shower the top which can lead to unphysical behaviour.

Cheers,

Olivier

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