The present Standard Model assumes that there are no more than three types (aka. These pairings consist of the electron/positron, muon/antimuon, tau/antitau, electron neutrino/electron antineutrino, muon neutrino/muan antinuetrino, and tau neutrino/tau antineutrino. In addition, all three leptons and their neutrinos have an associated antiparticle (antilepton).įor each, the antileptons have an identical mass, but all of the other properties are reversed. One observed cause has to do with “muon decay” (see below), a process where muons change their flavor to become electron neutrinos or tau neutrinos – depending on the circumstances. Muons, a type of lepton, shown being produced by the Large Hadron Collider. In all observed cases, the oscillations were confirmed by what appeared to be a deficit in the number of neutrinos being created. This can take a number of forms, which include solar neutrino, atmospheric neutrino, nuclear reactor, or beam oscillations. While each of the three lepton flavors are different and distinct (in terms of their interactions with other particles), they are not immutable.Ī neutrino can change its flavor, a process which is known as “neutrino flavor oscillation”. The different varieties of the elementary particles are commonly called “flavors”. Leptons have negative charge and a distinct mass, whereas their neutrinos have a neutral charge.Įlectrons are the lightest, with a mass of 0.000511 gigaelectronvolts (GeV), while Muons have a mass of 0.1066 Gev and Tau particles (the heaviest) have a mass of 1.777 Gev.
electron neutrino, muon neutrino, and tau neutrino). These include the Electron, the Muon, and Tau particles, as well as their associated neutrinos (i.e. Types of Leptons:Īccording to the Standard Model, there are six different types of leptons. Along with quarks, leptons are the basic building blocks of matter, and are therefore seen as “elementary particles”. These elementary particles are over 200 times more massive than electrons, but have only about one-ninth the the mass of a proton. Credit: Wikipedia Commons/MissMJ/PBS NOVA/Fermilab/Particle Data GroupThe term was chosen to refer to particles of small mass, since the only known leptons in Rosenfeld’s time were muons. The Standard Model of Particle Physics, showing all known elementary particles. In the book, he attributed the use of the word to a suggestion made by Danish chemist and physicist Prof. The first recorded use of the word was by physicist Leon Rosenfeld in his book Nuclear Forces (1948). The word lepton comes from the Greek leptos, which means “small”, “fine”, or “thin”. Where hadrons are composed of other elementary particles (quarks, anti-quarks, etc), leptons are elementary particles that exist on their own. According to this model, all matter in the Universe is composed of two kinds of particles: hadrons – from which Large Hadron Collider (LHC) gets its name – and leptons. Whereas the predominant theory used to be that all matter was made up of indivisible atoms, scientists began to realize that atoms are themselves composed of even smaller particles.įrom these investigations, the Standard Model of Particle Physics was born. In so doing, they quickly realized that the rules which govern them become increasingly blurry the deeper one goes. During the 19th and 20th centuries, physicists began to probe deep into the nature of matter and energy.
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