Delphes FastJet

[S. Niyogi]

Hello,

I am using Delphes v 3.3.2. Jet reconstruction is not working properly. Here is what I am doing.

I use calchep for WW production, shower/hadronise through pythia8, then analyze in Delphes (hepmc). Even if I let W decay to leptons (by force), there coming out to be lots of jets in the final state. I mean just by showering/ISR/FSR should not give such large number of jets from a leptonic final state.

So, I was looking into JetDefinition.cc and JetDefinition.hh. I was using delphes_card_CMS.tcl where it was written in line 490

# algorithm: 1 CDFJetClu, 2 MidPoint, 3 SIScone, 4 kt, 5 Cambridge/Aachen, 6 antikt

and default is 6 which I am using.
But, JetDefinition.hh uses completely different number assigned.
E.g. kt_algorithm=0,cambridge_algorithm=1,antikt_algorithm=2, etc.

Is this correct ?
Or, Am I making any mistake ? Shall I use the default cards in Delphes, or I have to make certain changes ? Thank you.

Regards,
Saurabh Niyogi

[Michele Selvaggi]

I am not sure I understand what is your problem. The jet definitions are fine, and they are defined in modules/FastJetFinder.

You don't have enough jets in the final state?
Are you sure you are producing an hadronized event file?

Can you attach a small hepmc or stdhep event file here so we can have a look?

[S. Niyogi]

Thanks for the reply.

I am doing a comparison between the processes

pp > w+ w- and gamma gamma > w+ w-

I am using calchep for event generation, pass through Pythia8 (ISR, FSR, Hadronization on) and then analyze in Delphes.

I expect much less jets in gamma initiated process. But this is not so. So, to check I decay W to leptons only, gamma gamma > e nu e nu*. Still I am getting many jets in the final state. I am attaching a small LHE file (hepmc file size is large). It contains 400 events. I am getting 216 0j event, 127 1j event, 36 2j events and so on. I am using delphes CMS card (all input default).

Regards,
Saurabh

[S. Niyogi]

Hi,

Is there any problem in my implementation? LHE file from calchep or madgraph after passing through Pythia8, I make root in delphes. I hope this procedure is correct.

Thanks,