The top quark is the last of the six quarks and the heaviest particle in the Standard Model. The mass of this elementary particle is almost as large as that of a gold atom, consisting of 79 protons and electrons, and about 118 neutrons.
The top quark was first theoretically predicted in 1973, but was not discovered until 22 years later at Fermilab in Chicago. Because of its large mass, the top quark requires, to be produced in the laboratory, very powerful accelerators that can reach very high energies.
The large mass of the top quark has numerous consequences: this quark decays immediately into a W boson and a bottom quark and is therefore unable to form bound states with other quarks. Furthermore, since the strength of the interaction with the Higgs boson is directly proportional to the mass, the top quark is the particle that interacts most strongly with the Higgs boson. Because of this strong coupling, we can investigate in more detail the Higgs boson’s properties by studying the Higgs decays in top quarks.
The top quark also plays an important role in the search for particles that have not been discovered yet. High-energy accelerators are used to search for increasingly heavier particles. Such heavy particles could either preferentially decay into top quarks (thus top quarks would help with the identification of new particles) or be produced together with top quarks (thereby, top quarks would appear as a disturbing background).
The signs show an example of the decay of a top quark pair in a particle detector. One top quark decays into a muon, a neutrino and a bottom quark (jet), the other into three jets.
