Flavor tagging

Inferring a quark flavor from the charges and identities of observed decay products. A mistaken assignment dilutes a flavour-dependent decay rate difference.

Bottom-quark jet tagging identifies jets compatible with containing a hadron carrying a bottom quark. A sufficiently long-lived bottom hadron travels away from the primary interaction before its particle decay, so displaced particle tracks and a secondary decay vertex provide evidence about its identity. A lepton within the jet can supply additional evidence. A top quark instead decays before hadronization.

A tag is a statistical classification, so both the efficiency for bottom jets and mistaken tags from charm quarks or light jets require calibration. That calibration concerns the flavor tagging response; it is not interchangeable with a calorimeter calibration of deposited energy. Control samples in collision data can measure the tagging efficiency for specified momentum and topology selections; those selections determine where the result applies.^[ref]