Heavy Quarks
Quark flavor tagging identifies the flavor of quark a jet comes from. B-tagging, the identification of bottom quarks, is the most important example. B-tagging relies on the b quark being the heaviest quark involved in a hadronic decay (tops are heavier but to have a top in a decay is necessary to produce some heavier particle to have a subsequent decay into a top). This implies that the b quark has a short lifetime and is possible to look for its decay vertex in the inner tracker. Additionally, its decay products are transversal to the beam, resulting in a high jet multiplicity. Charm tagging using similar techniques is also possible, but extremely difficult due to the lower mass. Tagging jets from lighter quarks is simply impossible, due to QCD background there are simply too many indistinguishable jets.
Read more about this topic: Particle Identification
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