SafekipediaLepton
Adapted from Wikipedia · Discoverer experience
In particle physics, a lepton is a tiny building block of the universe called an elementary particle. Leptons have a special kind of spin called half-integer spin, which means they spin at a rate of 1/2. Unlike some other particles, leptons do not join together through a very strong force called the strong interaction.
There are two main groups of leptons. The first group includes charged leptons, such as the electron, muon, and tauon. These particles can link up with other particles to make bigger structures like atoms. The second group is made of neutral leptons called neutrinos. Neutrinos hardly ever bump into anything, so they are very hard to spot. The most familiar lepton is the electron, which is a key part of everyday electricity and the structure of atoms.
Scientists have found six kinds of leptons, arranged in three groups. The lightest and most common is the electron, which never changes into anything else. Heavier leptons, like muons and taus, quickly turn into electrons and neutrinos. This happens because they change from a heavier form to a lighter one in a process called particle decay. Electrons are everywhere in the universe, while muons and taus can only be made in very powerful collisions, such as those caused by cosmic rays or in big machines called particle accelerators.
Etymology
The word "lepton" comes from the Greek word leptós, meaning "fine, small, thin." It was first used by a scientist named Léon Rosenfeld in 1948 to name tiny particles like electrons and neutrinos. Later, the muon was also called a lepton. These particles are much lighter than protons, with electrons and muons having small masses, while neutrinos have almost no mass at all.
History
See also: Electron § Discovery, Muon § History, and Tau (particle) § History
The first lepton found was the electron, discovered by J.J. Thomson and his team in 1897. Later, in 1930, Wolfgang Pauli suggested that an invisible particle, called the electron neutrino, helped keep important rules balanced during a process called beta decay.
In 1936, Carl D. Anderson found the muon. At first, it was thought to be a different kind of particle, but it was later grouped with electrons and neutrinos as leptons. In 1962, scientists showed that another type of neutrino exists, linked to the muon.
The tau was discovered between 1974 and 1977 by Martin Lewis Perl and his team. Scientists later found its matching neutrino in the year 2000. Today, scientists are looking for a possible fourth group of these particles, but none has been found yet.
| Particle name | Antiparticle name |
|---|---|
| electron | antielectron positron |
| electron neutrino | electron antineutrino |
| muon mu lepton mu | antimuon antimu lepton antimu |
| muon neutrino muonic neutrino mu neutrino | muon antineutrino muonic antineutrino mu antineutrino |
| tauon tau lepton tau | antitauon antitau lepton antitau |
| tauon neutrino tauonic neutrino tau neutrino | tauon antineutrino tauonic antineutrino tau antineutrino |
Properties
Leptons are tiny particles that spin in a special way — they have a spin of 1/2. This means they act like tiny magnets and follow special rules. Because of this spin, each lepton can only point in two directions: up or down.
Leptons come in two types. Charged leptons include the electron, muon, and tau, and they can stick to other particles to build bigger things, like the atoms that make up everything around us. Neutrinos are different — they hardly ever bump into anything else, so scientists don’t see them very often.
Charged leptons can feel a special kind of push and pull called the electromagnetic force, which helps them stick to other things. Neutrinos don’t feel this force, which is why they zip right through most matter without a hitch.
| ||||||
Universality
See also: LHCb experiment § Lepton flavour universality
Leptons, which are tiny particles with a spin of 1⁄2, interact with other particles in a special way. This means that no matter which lepton you look at, the way it interacts is the same. Scientists test this idea by studying how muons and tau particles break apart, especially in experiments like the Stanford Linear Collider and the Large Electron–Positron Collider.
They also look at how these particles decay, or break apart, and find that the patterns are very similar, though not exactly the same because of small differences in their weights. These studies help scientists understand the rules that govern these tiny particles.
Table of leptons
| Spin J [ħ] | Particle or antiparticle name | Symbol | Charge Q [e] | Lepton flavor number | Mass [MeV/c2] | Lifetime [s] | ||
|---|---|---|---|---|---|---|---|---|
| Le | Lμ | Lτ | ||||||
| 1/2 | electron | e− | −1 | +1 | 0 | 0 | 0.510998910(13) | stable |
| positron | e+ | +1 | −1 | |||||
| muon | μ− | −1 | 0 | +1 | 0 | 105.6583668(38) | 2.197019(21)×10−6 | |
| antimuon | μ+ | +1 | −1 | |||||
| tau | τ− | −1 | 0 | 0 | +1 | 1776.84(17) | 2.906(10)×10−13 | |
| antitau | τ+ | +1 | −1 | |||||
| electron neutrino | ν e | 0 | +1 | 0 | 0 | unknown | ||
| electron antineutrino | ν e | −1 | ||||||
| muon neutrino | ν μ | 0 | +1 | 0 | unknown | |||
| muon antineutrino | ν μ | −1 | ||||||
| tau neutrino | ν τ | 0 | 0 | +1 | unknown | |||
| tau antineutrino | ν τ | −1 | ||||||
Related articles
This article is a child-friendly adaptation of the Wikipedia article on Lepton, available under CC BY-SA 4.0.
Images from Wikimedia Commons. Tap any image to view credits and license.