ParameterR and DeltaR

[namgyun]

hello

I confuse ParameterR and DeltaR.
now I study about ttbar sample
and use anti kt algorithm delta R=0.7
but in the delphes_card_CMS.tcl, I don't know handling parameters.

1. what is the definition of parameterR , parameterR and algorithm deltaR have same meaning?

2. actually, I want to get B tagging Pt distribution

but when I used parameterR=0.5 and deltaR=0.5 , the number of events is too small.

help Me

[Michele Selvaggi]

Hi,

ParameterR is simply the jet cone size, and is a parameter of the clustering algorithm.
deltaR is the matching criterion used in the b-tagging module to match the reconstructed jet with b-partons.
I would use similar values for the two, although having parameterR=0.7 and deltaR=0.5 should not give issues.
What do you mean by "number of events is too small" ?
If you want higher b-tagging efficiency you can simply change the formula in the b-tagging module

Michele

[namgyun]

Thank you Michele.

and then, deltaR(CMS note or twiki) and parameterR(delphes_card_CMS.tcl) are same?

and mentioned b-tagging module is in module folder? or b tagging section in ther card?

• nam

[Michele Selvaggi]

You can choose them same but it's not compulsory.
Yes, the btagging module I was mentionning is the b tagging section in the card.
More specifically, you might want to change these formulae:

add EfficiencyFormula {0} {0.001}

# efficiency formula for c-jets (misidentification rate)
add EfficiencyFormula {4} {                                      (pt <= 15.0) * (0.000) +
                                                (abs(eta) <= 1.2) * (pt > 15.0) * (0.2*tanh(pt*0.03 - 0.4)) +
                              (abs(eta) > 1.2 && abs(eta) <= 2.5) * (pt > 15.0) * (0.1*tanh(pt*0.03 - 0.4)) +
                              (abs(eta) > 2.5)                                  * (0.000)}

# efficiency formula for b-jets
add EfficiencyFormula {5} {                                      (pt <= 15.0) * (0.000) +
                                                (abs(eta) <= 1.2) * (pt > 15.0) * (0.5*tanh(pt*0.03 - 0.4)) +
                              (abs(eta) > 1.2 && abs(eta) <= 2.5) * (pt > 15.0) * (0.4*tanh(pt*0.03 - 0.4)) +
                              (abs(eta) > 2.5)                                  * (0.000)}
}

be aware that {5} is the btagging efficiency, and {4} {0} are respectively c and light mistag rates.

[namgyun]

Thank you so much Michele.

ok, I understand using B tagging in the card.

but deltaR is still confused me .

you mentioned "ParameterR is the jet cone size", it's ok

but if deltaR is matching criterion, what is the deltaR 's function ? and relation with ParameterR?

Could you explain?

nam

[Michele Selvaggi]

I assume you are talking about the deltaR parameter in the b-tagging module.

If a jet is found to be at distance DeltaR = sqrt((phi_jet - phi_parton)^{2 + (eta_jet - eta_parton)}2) from the parton of interest (b, if not c, if not light) it becomes a candidate for b-tagging.
At that point we evaluate the probability (given its pt and eta) for it to be b-tagged by using the function above, and throw a dice.

Clear enough?
Michele

[namgyun]

Thank you very much Michele.

I understand.