Leptons are elementary particles, meaning they are not made up of smaller particles.
There are six known types of lepton (12 if you count antiparticles). Three of these are negatively charged particles: ELECTRON, muons and tau particles. The other three are neutrinos, which are electrically neutral. There is a neutrino corresponding to each type of charged lepton, so we have the electron neutrino, the muon neutrino and the tau neutrino.
Leptons are a crucial part of Standard model of particle physics. Electrons are important components of atomwhile the neutrinos flood in The universe and are produced by nuclear fusion reactions in stars as well as by particle decomposition.
In connection with: 10 Surprising Things You Should Know About Quantum Physics
What is the Lepton number?
An example of leptons involved in particle decay is the decay of a neutron. neutron are stable when bound to other neutrons and proton in atomic nuclei, but when alone outside atomic nuclei they are unstable and degradation after about 15 minutes (opens in a new tab) into a proton, an electron, and an antielectron neutrino.
This decay reaction demonstrates some of the fundamental properties of leptons. First, it conserves a property known as the Lepton Number, which is defined by physicists at Georgia State University (opens in a new tab) as the number of leptons minus the number of antileptons. A neutron is a baryon, not a lepton, so its lepton number is 0. Therefore, its decay products must also add up to a lepton number of 0. An electron’s lepton number is 1, and the of leptons of an anti-neutrino. is –1, so it cancels out and conserves the total number of leptons of the reaction.
Complicating things are the three families of leptons (electron and electron neutrinos, muons and muon neutrinos and tau particles and tau neutrinos) and the lepton number rules say they cannot be mixed and matched. So a neutron could never decay and produce an electron and an anti-muon neutrino, because they belong to different families of leptons.
However, once an anti-electron neutrino is produced from the decay of a neutron, the neutrino itself can change flavor into a muon or tau neutrino. This is called neutrino oscillation and is described by physicists at Stanford University’s Neutrino Group (opens in a new tab). Neutrino oscillations are solution to the mystery of the solar neutrino problem (opens in a new tab)where only a third of the expected number of electron neutrinos appeared to originate sun reached Earth. It turned out that they were not disappearing, but oscillating into muon and tau neutrinos on their way here.
Properties of leptons
The electron was the first lepton discovered in 1897 by the British physicist. Joseph John Thomson (opens in a new tab). An electron has a rest mass energy of 0.511 MeV (opens in a new tab) (Mega electron-Volt) (which is equivalent to 9.1 x 10^–31 kilograms). Electrons are important components of atoms, orbiting around the nucleus of an atom composed of protons and neutrons. An atom will have the same number of electrons as protons, ensuring that
the positive charges on the protons and the negative charges on the electrons cancel out to create an electrically neutral atom. Many chemical processes are related to the presence of these electrons in atoms.
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The muons were discovered in 1936 (opens in a new tab) by Carl Anderson and Seth Neddermeyer, who were experimenting with cosmic rays from deep space (Anderson had already discovered the antiparticle of the electron, positron (opens in a new tab), four years earlier). A cosmic ray is a misnomer – it’s not a “ray” but a particle of extremely high energy produced by violent processes in the universe, such as quasars, supernovae and highly magnetized ones. supernova remains. When the cosmic rays come in Earth’s atmosphere, collide with atmospheric molecules and break apart, producing a shower of daughter particles created in the collision. Muons are among these daughter particles, but they are short-lived, decaying back to an electron after only 2.2 million seconds. Fortunately, because I travel almost to speed of lightthey can reach the Earth’s surface before decaying, allowing scientists to detect them.
Muons are more massive than electrons; More precisely, 207 times more massive, with a rest mass-energy of 105.7 MeV (opens in a new tab) (equivalent to 1.9 x 10^–28 kg).
Tau particles were discovered by Martin Perl particle accelerator experiments in 1975 (opens in a new tab) and, like muons, they are also created only in violent collisions of particles. Tau particles are even more massive than muons, with a rest mass energy of 1,777 MeV (opens in a new tab) (equivalent to 3.1x 10^–27 kg) which means they are approx 3,700 times more massive than an electron (opens in a new tab). Like muons, tau particles have incredibly short lifetimes and decay after just 29 trillionths of a second (opens in a new tab). You literally blink and you’ll miss them, which is why they took so much longer to be detected.
The name “lepton” was coined in 1948 by a physicist Leon Rosenfeld (opens in a new tab) and the last lepton to be discovered, the tau neutrino, was found as early as 2000. The Standard Model does not predict that there will be any more leptons, although there have been some suggestions that there might be a hypothetical fourth type of neutrino called the sterile neutrino . The sterile neutrino is a possible explanation for the identity dark matter. If sterile neutrinos do exist, then it would be a hint of physics beyond the Standard Model.
Important difference between leptons and quarks
Leptons are fermions, meaning they have a spin of 1/2 (fermions have half-integer quantum spins, ie 1/2 or 3/2). quarks – which are the building blocks of protons and neutrons that form the basis of atomic nuclei – are also fermions and elementary particles. So is there any difference between leptons and quarks?
Yes it is. Crucially, quarks are the only particles that experience all four fundamental forces: strong nuclear force, weak interaction, electromagnetic force and gravity. Leptons, on the other hand, experience only three of them: the weak interaction, the electromagnetic force, and gravity.
The strong force is the glue that binds quarks together to form atomic nuclei. Because of this, no quark can exist in isolation. Because leptons do not feel the strong force, they are free to exist on their own, outside of atoms, floating through space. Although muons and tau particles do not exist long enough before decaying through the weak interaction to make the most of their freedom, free electrons and neutrinos are key components of the particle universe.
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Free electrons, for example, scatter photons. When the universe was very young and hot, space-bar it was covered in light-scattering free electrons, meaning photons couldn’t travel any appreciable distance and the universe remained pretty dark. About 379,000 years after The big explosion, the universe had cooled enough for atomic nuclei to combine with electrons to form complete atoms of hydrogen and helium. With most of the free electrons swept away, that path was cleared to allow photons to finally travel through space unhindered. These first photons are what we see today as being cosmic microwave background (CMB) radiation that tells us so much about the very early universe and the Big Bang.
Of course, there are still many free electrons today; the energy of a photon impacting an atom may be sufficient to release an electron and “ionize” the atom. Inside Earth’s Sun, where temperatures can reach 27 million degrees Fahrenheit (15 million degrees Celsius) in the core, such collisions occur in all time. Photons of energy generated in the core of the sun by nuclear fusion reactions continuously scatter free electrons inside the sun’s inner “radiative zone”, which means that, depending on the assumptions you use in your calculations, they can take anywhere between 4,000 years (opens in a new tab) and a million years (opens in a new tab) to reach the surface of the sun and be emitted as light. As a result, the sunlight we see is very old indeed!
Explore the standard model of particle physics in more detail with these resources from Department of Energy (opens in a new tab). Learn more about leptons with chemeurope.com (opens in a new tab), a specialized portal for the chemical sector. Delve into particle physics with this free online learning course from The Open University (opens in a new tab).
Particle Physics, by Brian R. Martin (2011, One-World Publications)