How to write a root file for some specific tagged events only?

[Debashis Saha]

Hi,
Is it possible to create a .root file for events with some particular signatures? Actually, if we generate a general root file, information of all the events is getting stored in the file, thereby taking a huge unaffordable disk space. So, I am wondering whether there is any way to store only the events (say, events with 1 b-jet) in which we are interested in.

P.S: I am using DelphesPythia8 to create the root file.
Thanks

[Michele Selvaggi]

Hi,

it not possible to do what you ask INSIDE Delphes. The actual way of doing it would be to write a ROOT macro that creates a simplified tree that contains only the interesting event/variables. This said if you have problems of disk space, I would suggest you to not store collections that you don't use later. Usually these are Genparticle, Towers, Tracks, etc.. You can do this by commenting the relevant TreeWriter section in the card:

# add Branch Delphes/allParticles Particle GenParticle

#  add Branch TrackMerger/tracks Track Track
#  add Branch Calorimeter/towers Tower Tower

#  add Branch Calorimeter/eflowTracks EFlowTrack Track
#  add Branch Calorimeter/eflowPhotons EFlowPhoton Tower
#  add Branch Calorimeter/eflowNeutralHadrons EFlowNeutralHadron Tower

This should save you a lot of disk space.

Cheers,
Michele