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A reconstructed physics object is considered isolated if its track and/or energy deposits in the calorimeter are well-separated from any others not associated with the object. Isolation requirements can help reduce background due to misidentified or non-prompt objects or genuine objects overlapping too much to guarantee proper reconstruction.

The precise criteria for isolation depend on the analysis needs.

Isolation algorithms

Many isolation algorithms define an isolation cone centered about the direction of the object and requires that the summed energy deposits or track momenta not associated with the object of interest within this cone are below some isolation cutoff. The cutoff value is often dependent on the momentum of the object of interest, e.g. a fixed fraction of it.