Key Points
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CMS Physics Objects
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CMS physics objects include: muons, electrons, taus, photons, and jets.
Missing transverse momentum is derived from physics objects (negative vector sum).
Objects are stored in separate collections in the AOD files
Objects can be accessed one-by-one via a for loop
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Accessing common quantities
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Physics objects in CMS inherit common member functions for the 4-vector quantities of transverse momentum, polar/azimuthal angles, and mass/energy.
Objects are matched to generator-level particles based on spatial relationships.
Other quantities such as impact parameters and charge have common member functions.
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Accessing CMS-specific object information
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Physics objects in CMS are reconstructed from detector signals and are never 100% certain!
Identification and isolation algorithms are important for reducing fake objects.
Member functions for these algorithms are documented on public TWiki pages.
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Glossary
Physics object: an instance of a software class representing an electron, muon, tau, photon, or jet as reconstructed in a detector.
CMS: the Compact Muon Solenoid detector