JER Corrections

[shane-breeze]

Is the recommended smearing procedure [1] for jet energy resolution applied to the Jet collection in nanoAOD or should this be applied on-the-fly to this collection?

[1] https://twiki.cern.ch/twiki/bin/view/CMS/JetResolution#Smearing_procedures

[ktht]

There's a nanoAOD-tools module for that (link).

[peruzzim]

It's not applied in production, it would be very nice to have it.
The recommended procedure applies a random smearing for jets not matched to any generator-level jet, which is not ok for reproducibility.

For those cases, we should rather use a semi-deterministic approach as it is done for the EGM smearings (see EgammaAnalysis/ElectronTools/plugins/CalibratedElectronProducersRun2.cc).
In order to set the seed, we should use only variables for which precision is not lost in the nanoAOD production (so that one could later reproduce its behaviour in nanoAOD-tools module - avoid pt, phi etc.).

Would you please try implementing that in a producer?

[peruzzim]

@zdemirag @ahinzmann would you agree?

[ahinzmann]

A semi-deterministic approach is certainly better.
And keeping the ability to apply new JER factors on top of NanoAOD (since those typically come later than the JEC corrections).
Putting also @rappoccio @eioannou in the loop here.

[zdemirag]

I also agree that to some level a deterministic approach is good way to go. In the this PR: cms-sw#20240 an option was added to the templates class to achieve the deterministic JER application. @eioannou: specifically this might be useful for the smeared MET and @rappoccio was part of this conversation in the past for the PR.

[mariadalfonso]

This topic is discussed in the context of the correction-lib to be added post-nano.
see here
cms-nanoAOD/correctionlib#130
@zdemirag @ahinzmann you might want to contribute there

I close this topic as nano-content will not be modified.