Same Delphes simulation with different jet clustering

[Matias Vazquez]

Dear Delphes developers,

I am new with the Delphes package so my question might be trivial...
Suppose that I generate events using MG5+pythia, being the result of this a pythia_events.hep file. Then I want to run a detector simulation with Delphes, but when doing the jet clustering via FastJet (inside delphes), I want two (or more) different outputs: one with the parameterR for the Jet finding = 0.6 , say, and another one with a different one, e.g. 0.2. One solution could be just running Delphes twice on the events file, but my impression is that there is some MC, therefore random stuff, going on inside the detector simulation, thus both outputs are not really comparable.

Am I correct? how can I run 2 different jet clustering algorithms with the same detector simulation?

Many thanks in advance!
Matias.

[Michele Selvaggi]

Hi Matias,

If you want to run two identical simulations you should add

set RandomSeed 123

at the beginning of the card.
This said you can always change the card in a way that the output contains two jet collections.

Michele

[Matias Vazquez]

Hi Michele,

Thank you very much for your reply. So, if I understood well, you propose to run delphes twice on the events, each run with different options in the 'Jet finder' block but adding in both cards this RandomSeed 123 thing at the beggining. This way it guarantees that both simulations will have identical results, is that it?

Thanks!

Matias

[Matias Vazquez]

Replying to mselvaggi:

Hi Matias,

If you want to run two identical simulations you should add

set RandomSeed 123

at the beginning of the card.
This said you can always change the card in a way that the output contains two jet collections.

Michele

Hi Michele,

Thank you very much for your reply. So, if I understood well, you propose to run delphes twice on the events, each run with different options in the 'Jet finder' block but adding in both cards this RandomSeed? 123 thing at the beggining. This way it guarantees that both simulations will have identical results, is that it?

Thanks!

Matias

[Michele Selvaggi]

Hi Matias,

yes setting the seed to some fixed value ensures that the same set of random numbers will be thrown during the simulation every time, which will result in the same output, if all other things are kept unchanged.

Michele