dR between leptons and Jets after delphes

[teddy]

Hi:

In the delphes cards, in the anti-kT algorithm, the parameter:

ParameterR 0.5

will control the distance between two jets and also between jet and lepton ( Right? )

But when I plot the distribution of dR_jj and dR_jl, I find that there are several pairs of jets having dR_jj < 0.5, and several pairs of jet and lepton having dR_jl < 0.5.

How does this happen?

Thanks very much!

[Michele Selvaggi]

Hi,

sorry for late reply.
Rparameter is just an algorithm parameter, it does not mean that the jets ALWAYS have a cone radius of R.
Moreover, it can be also be that you have non-isolated leptons inside jets.

However, the fraction of DR_jj and DR_jl should be small, is it what you observe?

Michele

[teddy]

Yes the fraction of small dR_jj and dR_jl is very small.

Further, I have another question, if we want to require jets to have PT larger than 30 GeV, should we implement this cuts after delphes, or change the parameter JetPTMin in Jet algorithm? Do these two methods have differences?

Thanks!

[Michele Selvaggi]

Hi, in principle these two methods may present a small difference if you are applying some jet energy scale.

Say you have JetPTMin = 20.0 and then you apply a constant JetEnergyScale factor of 1.2. This will result in an implicit cut on jets pT > 24 GeV. So in this case if you want to do things properly, you have to set a JetPTMin to some value < 16.666 GeV.

If the JetEnergyScale factor is set to 1.0, then it makes no difference if you apply your cut in or outside Delphes.
As a personal preference, I would apply set JetPTMin = 20 and apply a cut pt > 30 GeV after, since it leaves you more freedom (also considering the Jet collection represent a very tiny fraction of the output size).

Michele