MadGraph5_aMC@NLO

How many generated particles to expect?

Asked by Aidan Wiederhold

Hi.

If I generate a process as such:
generate p p > z, z > e+ e-
add process p p > z, z mu+ mu-

and output via pythia8 and then Delphes.

Then is it guaranteed that in every event a Z boson will be generated and decay via one of these modes? Or will only a fraction of the events actually have this Z boson created?

So in the genParticle branch of the Delphes output will I find as many Z bosons as events, or less?

Thanks.

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Olivier Mattelaer (olivier-mattelaer) said : 		#1

Hi,

MG5aMC will only generate events with Z-boson and pythia will only shower such events.
Now I guess that the detector can loose the Z boson for any detector related reason (gap in the detector,....)
So out of Delphes, It would make sense that you have tracks that are missing and therefore a lot of funny scenario are possible.

>So in the genParticle branch of the Delphes output will I find as many Z bosons as events, or less?

For such technical question, you should ask Delphes author, I have no clue what is the information in that branch.

Cheers,

Olivier

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Aidan Wiederhold (aidan-wiederhold) said : 		#2

Hi,

Thanks for your reply.

I haven't contacted the Delphes author but I think you/I can answer the full question now. After fixing the code I had written to analyse this data I was able to find a lepton pair in each event in the genParticle branch. The genParticle branch contains the data of the particles that were generated in the simulation, so as far as I can tell the particles in genParticle are the simulation analogue to the particles that interact inside the detector before detection, so they represent "what is really going on". Then the other branches such as "electron" and "muon" are the analogue to the detected signals and subsequent reconstruction of the particle responsible for those signals.

So in the genParticle branch I extract the leptons from a Z -> l+ l- in every single event, but naturally, and as you also said, they are not all detected by the detector and so in the electron/muon branches I don't always find leptons from this decay.

Hopefully this answer is correct and helpful for others in future.

Thanks,
Aidan