![]() The reaction pictured is experimentally identifiable because the on-shell $Z$ decays to an lepton pair with a mass of 90 GeV and the Higgs decays to a limited choice of end states that are mostly reconstructable and add up to the Higgs mass.Ī surprising amount of collider physics is not so much about what can happen as about what can be uniquely shown to have happened.įinally, I would certainly not describe this reaction as a "decay". The lepton pair can annihilate directly to the Higgs, but the event is experimentally identical to annihilation to photons or $Z^0$s (because the thing that makes a coupling possible is that both side have compatible quantum numbers, so that (at tree level) all three possibilities decay to very similar end states). All non-leptons have a lepton number of zero. So, a positron has a lepton number of -1. Anti-leptons have negative lepton numbers. ![]() So does a muon, a tau, and each of the three flavors of neutrinos. So, an electron has a lepton number of 1. The electron and positron form a particle and anti. Lepton number simply refers to the number of leptons present. For the anti-particles and anti-neutrinos, its value is -1. The lepton number for neutrinos is also equal to unity. The lifetime of the muon is 2.20 microseconds. All the members of the lepton family-electron(e), muon (), taon () are assigned a specific value called the ‘Lepton number’ and for these particles its value is 1. The fact that the above decay is a three-particle decay is an example of the conservation of lepton number there must be one electron neutrino and one muon neutrino. ![]() virtual or having the "wrong" mass).Īt the second vertex the $Z^0$ is put "on-shell" by the emission of a Higgs (note, however, that it will decay very quickly in any case). The muon is a lepton which decays to form an electron or positron. The $^*$ notation does not mean excited in this case, it means "off shell" (i.e. Thats what lepton universality means, and its why the branching ratio is the same for electron-positron pairs, muon-antimuon pairs and tau-antitau pairs.
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