Lepton number

The lepton number of particle physics, a charge -like quantum number of elementary particles, is defined as the difference in the number of leptons and the number of antileptons:

Thus it is:

• For single leptons: and
• For individual antileptons.

Analogously, for each family of leptons a separate Leptonenfamilienzahl define (English: Leptonic family number, also often referred to briefly as lepton number ) to which only count the particles and the antiparticles of each family. Specifically, these are:

• The electronic lepton number
• The muonic lepton number
• Tauonische the lepton number.

In summary,.

Leptonenzahlen as conserved quantities

In many physical models, especially in the standard model of elementary particle physics, the lepton number is preserved, since all interactions get the Leptonenzahlen. When drawing Feynman diagrams is to ensure that remain at each vertex get the Leptonenzahlen.

If one considers, for example, the decay, the initial state has the Leptonenzahlen, and because the neutron is not a lepton. In the final state before are: a proton (no lepton ) with an electron with and an anti- electron neutrino with (all other Leptonenzahlen are respectively 0). So also the final state for all three families each has the Leptonenfamilienzahl 0 ( specially ). The leptons is also obtained as the sum of Leptonenfamilienzahlen in this example.

For a long time were thought to be massless neutrinos for. In this case, the lepton number is preserved not only as a whole but also for each individual family. Have a neutrino mass, the mass matrix is not necessarily diagonal in the basis of the individual Leptonfamilien and neutrino oscillations can occur and so leptons of different families are transformed into each other, so that only the Gesamtleptonenzahl is still preserved. If it is in the neutrino Majorana fermions to (ie, the neutrino is its own antiparticle ), a neutrino -less double beta decay is possible that violates the lepton number conservation by two units.

When (not yet observed ) proton decay and baryogenesis during the big bang is not conserved lepton. The lepton number is hence may not be strictly maintained. In most versions of the Grand Unified Theory (GUT), however, the difference of baryon and lepton number BL remains strictly obtain at least.

• Particle Physics