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Jets 101
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Jet is a physical object representing hadronic showers interacting with our detectors. A jet is usually associated with the physical representation of quark and gluons, but they can be more than that depending of their origin and the algorithm used to define them.
A jet is defined by its reclustering algorithm and its constituents. In current experiments, jets are reclusted using the anti-kt algorithm. Depending on their constituents, in CMS, we called jets reclustered from genparticles as GenJets, calorimeter clusters as CaloJets, and particle flow candidates as PFJets.
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Pileup Reweighting and Pileup Mitigation
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We call pileup to the amount of other processes not coming from the main interaction point. We must mitigates its effects to reduce the amount of noise in our events.
Many event variables help us to learn how different pileup was during the data taking period, compared to the pileup that we use in our simulations. The pileup reweighting procedure help us to calibrate the pileup profile in our simulations.
The so-called jetID is the basic jet quality criteria to remove fake jets.
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Jet energy corrections and resolution
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The energy of jets in data and simulations is different, for many reasons, and in CMS we calibrate them in a series of steps.
Jets are stochastic objects which its content fluctuates a lot. We measure the jet energy resolution to mitigate this effects.
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Jet Substructure
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Jet substructure is the field study the internakl structure of high pt jets, usually clustered with a bigger jet radius (AK8).
Grooming algorithms like softdrop, and substructure variables like the nsubjettiness ratio help us to identify the origin of these jets.
Over the years more state-of-the-art taggers involving ML have been implemented in CMS. Those help us indentify more effectively boosted jets.
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