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# Lepton

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 Sub Topics Leptons are the another class of elementary particles besides the quarks. Like quarks there are three families of leptons. Each lepton family consists of negatively charged particle and extremely light particle. They are affected by the gravitational, electromagnetic and weak forces but not by a strong force. They must be either created or destroyed in the particle-anti-particle pairs, the total number of leptons is conserved in all processes. Let's see more about them.

## What is a Lepton?

A lepton is the major elementary particles like quarks and bosons. These leptons are believed to be fundamental units of matter, i.e., the particle do have no more smaller units. These six leptons come in pairs, each pair consisting of one charged lepton and one neutral lepton. The neutral lepton is called a neutrino. Each pair is called a generation and in each generation the mass of the neutrino is much less than the mass of the charged lepton. Electrons, muons and taus have a negative electric charge. Muons and taus have a much larger mass than that of electrons. A muon is about 207 times as heavy as electrons and tau is about 3490 times as heavy as an electron.

 Generation Particle Charge Mass 1 Electron (e)Electron neutrino ($\nu_e$) -10 0.51 MevLess than 50 ev 2 Muon ($\mu$)Muon neutrino ($\nu_\mu$) -10 106 MevLess than 0.5 Mev 3 tau ($\tau$)tau neutrino ($\nu_r$) -10 1784 MevLess than 160 Mev

## Lepton Number

Each lepton generation has its own lepton number. The lepton number for electron is electronic number for the electron and electron neutrino denoted as $L_{e}$. The lepton number for muon is muonic number for muon and muon neutrino denoted as $L_{\mu}$. The lepton number for tau is tauonic number for tau and tau neutrino denoted as $L_{\tau}$.

Lepton number is the number of leptons minus number of antileptons. It is given as
L = $n_{\iota}$ - $n_{\bar{\iota}}$
where,
$n_{\iota}$ is the lepton,
$n_{\bar{\iota}}$ is the antilepton.