CMS Physics Objects
- Physics objects are the final abstraction in the detector that can
be associated to physical entities like particles.
- NanoAOD stores physics object properties as branches of a ROOT tree,
linked by common name prefixes.
- Quantities such as impact parameters and charge have common member
functions.
- Physics objects in CMS are reconstructed from detector signals and
are never 100% certain!
- Identification and isolation algorithms are important for reducing
fake objects.
- Track access may differ, but track-related member functions are
common across objects.
- Physics objects in CMS are reconstructed from detector signals and
are never 100% certain!
- Muons typically use pre-configured identification and isolation
variables”
- Jets are spatially-grouped collections of particles that traversed
the CMS detector
- Particles from additional proton-proton collisions (pileup) must be
removed from jets
- Missing transverse energy is the negative vector sum of particle
candidates
- Many of the variables discussed for other objects also exist for
jets
- Tagging algorithms separate heavy flavor jets from jets produced by
the hadronization of light quarks and gluons
- FatJet tagging algorithms can identify jets from massive SM
particles
- Tagging algorithms produce a disriminator value for each jet that
represents the likelihood that the jet came from a particular
particle
- Each tagging algorithm has recommended ‘working points’
(discriminator values) based on a misidentification probability for
non-interesting jets
- Jet energy corrections are factorized and account for many
mismeasurement effects
- L1+L2+L3 should be applied to jets used for analyses, with residual
corrections for data
- Jet energy resolution in simulation is typically too narrow and is
smeared using scale factors
- Jet energy and resolution corrections are sources of systematic
error and uncertainties should be evaluated
- In general, the jet corrections are significant and lower the
momenta of the jets with standard LHC pileup conditions
- For most jets, the JES uncertainty dominates over the JER
uncertainty
- In the endcap region of the detector, the JER uncertainty in larger
and matches the JES uncertainty
