Electron

Electron Stats

  • Symbol: e−
  • Generation: First
  • Type: Charged
  • Antiparticle: Positron
  • Mass: 30.5 MeV/c²
  • Charge: -1
  • Antiparticle Charge: +1
  • Colors: None
  • Lifetime: Stable

The Electron

The electron (symbol: e−) is the least massive of the charged leptons and a major constituent of everyday matter. Atoms, the basic building blocks of matter, are composed of a dense central nucleus made of positively charged protons (two up quarks, one down quark) and electrically neutral neutrons (two down quarks, one up quark); this nucleus is then surrounded by a cloud of negatively charged electrons.

The electron is part of the first generation of matter, has an electric charge of -1 e and a bare mass of 0.5 MeV/c². Like all leptons, the electron is a fundamental fermion with spin 1⁄2. As a charged lepton, the electron experiences three of the four fundamental interactions: gravitation, electromagnetism, and the weak force.

The antiparticle of the electron is called the positron which differs from the electron only in that its electrical charge and some other properties have equal magnitude but opposite sign. Electrons are denoted by e− and positrons by e+. Like all charged leptons, the electron is associated with a neutrino (non-charged/neutral lepton), the electron neutrino. Electron neutrinos are denoted by νe.

History

In the mid-1800s, British natural philosopher Richard Laming developed the idea that an atom is composed of a core of matter surrounded by subatomic particles that had unit electric charges. In 1874, Irish physicist George Johnstone Stoney suggested that there was a "single definite quantity of electricity"; however, Stoney believed these charges were attached to atoms themselves. In 1881, German physicist Hermann von Helmholtz argued that both positive and negative charges were divided into elementary parts. In 1891 Stoney coined the term electron to describe these elementary charges, the word electron is a combination of the words electr(ic) and (i)on.

In 1896, the British physicist J. J. Thomson, and his colleagues performed experiments indicating that cathode rays were unique particles, as opposed to waves, atoms or molecules as earlier believed. Thomson made good estimates of both the charge e and the mass m, finding that cathode ray particles, which he called "corpuscles," were approximately one-thousandth the mass of the smallest known ion: hydrogen. The Irish physicist George F. Fitzgerald again proposed the name electron for these particles, and the name has since gained universal acceptance.

Electron Neutrino

Electron Neutrino Stats

  • Symbol: νe
  • Generation: First
  • Type: Neutral
  • Antiparticle: Electron Antineutrino
  • Mass: <2×10-6 MeV/c²
  • Charge: None
  • Antiparticle Charge: None
  • Colors: None
  • Lifetime: ?

The Electron Neutrino

The electron neutrino (symbol: νe) is the least massive of all the neutrinos. Electron neutrinos can be observed in instances of radioactive decay called beta decay (β decay), in which a beta particle (an electron or a positron) is emitted from an atomic nucleus along with either an electron neutrino (if it's positron emission) or an electron antineutrino (if it's electron emission).

The electron neutrino is part of the first generation of matter, and has an estimated bare mass of <2×10-6 MeV/c². Like all leptons, the electron neutrino is a fundamental fermion with spin-1⁄2. Being a neutrino, the electron neutrino experiences only two of the four fundamental interactions: gravitation, and the weak force. Electron Neutrinos do not participate with the electromagnetic force and therefore have no electric charge.

The antiparticle of the electron neutrino is the electron antineutrino, which differs from the electron neutrino only in that some of its properties have equal magnitude but opposite sign.

History

The process of beta decay produces both beta particles and electron antineutrinos. Wolfgang Pauli proposed the existence of these particles, in 1930, to ensure that beta decay conserved energy and momentum. The electron neutrino and its anti particle- the electron antineutrino were discovered in 1956 by a team led by Clyde Cowan and Frederick Reines (Cowan–Reines neutrino experiment).

Muon

Muon Stats

  • Symbol: μ−
  • Generation: Second
  • Type: Charged
  • Antiparticle: Antimuon
  • Mass: 105.7 MeV/c²
  • Charge: -1
  • Antiparticle Charge: +1
  • Colors: None
  • Lifetime: 2.2 microseconds
  • Decays to: e- + νe + νμ

The Muon

The muon, from the Greek letter mu (μ) used to represent it, is a charged lepton, similar to the electron, but with much more mass. Since the muon's interactions are very similar to those of the electron, a muon can be thought of as an ustable, heavier version of the electron. Of the charged leptons, the muon is more massive than the electron but less massive than the tau. The muon is unstable and decays rapidly, with a lifetime of only 2.2 microseconds (1 microsecond = 10-6 of a second).

The muon is part of the second generation of matter, has an electric charge of -1 e and a bare mass of 105.7 MeV/c² which is equivalent to the mass of approximately 200 electrons. Like all leptons, the muon is a fundamental fermion with spin 1⁄2. As a charged lepton, the muon experiences three of the four fundamental interactions: gravitation, electromagnetism, and the weak force.

The antiparticle of the muon is called the antimuon which differs from the muon only in that its electrical charge and some other properties have equal magnitude but opposite sign. Muons are denoted by μ− and antimuons by μ+. Like all charged leptons, the electron is associated with a neutrino (non-charged/neutral lepton), the electron neutrino. Muon neutrinos are denoted by νe.

History

Muons were discovered by Carl D. Anderson and Seth Neddermeyer at Caltech in 1936, while studying cosmic radiation. Anderson initially called the new particle a mesotron, but as more particles with these traits were discovered in accelerator experiments later on, they became collectively known as mesons. With the rise of the codified Standard Model in the 1970s, all mesons other than the mu meson were finally understood to be hadrons—that is, non-fundametal (composite) particles made of quarks. Mu mesons, however, had shown themselves to be fundamental particles (leptons) like electrons, with no quark substructure. Thus, mu mesons were not mesons at all, and the term mu meson was altogether abandoned and replaced by the modern term “muon.” The existence of the mu meson, or the muon as we now know it, was confirmed in 1937 by J. C. Street and E. C. Stevenson's cloud chamber experiment.

Muon Neutrino

Muon Neutrino Stats

  • Symbol: νμ
  • Generation: Second
  • Type: Neutral
  • Antiparticle: Muon Antineutrino
  • Mass: <0.17 MeV/c²
  • Charge: None
  • Antiparticle Charge: None
  • Colors: None
  • Lifetime: ?

The Muon Neutrino

The muon neutrino (symbol: νμ) is more massive than the electron neutrino and less massive than the tau neutrino. Muon neutrino interactions, or interactions in which muon neutrinos are produced, are not common in the relatively low-energy world we experience in everyday life, but have been measured as the products of high-energy reactions in particle accelerators.

The muon neutrino is part of the second generation of matter, and has an estimated bare mass of <0.17 MeV/c². Like all leptons, the muon neutrino is a fundamental fermion with spin 1⁄2. Being a neutrino, the muon neutrino experiences only two of the four fundamental interactions: gravitation, and the weak force. Muon Neutrinos do not participate with the electromagnetic force and therefore have no electric charge.

The antiparticle of the muon neutrino is the muon antineutrino , which differs from the muon neutrino only in that some of its properties have equal magnitude but opposite sign.

History

In 1962 Leon M. Lederman, Melvin Schwartz and Jack Steinberger proved the existence of more than one type of neutrino by first detecting interactions of the muon neutrino, earning them the 1988 Nobel Prize.

Tau

Tau Stats

  • Symbol: t−
  • Generation: Third
  • Type: Charged
  • Antiparticle: Antimuon
  • Mass: 1776.8 MeV/c²
  • Charge: -1
  • Antiparticle Charge: +1
  • Colors: None
  • Lifetime: 300 fs
  • Decays to: tau decay modes

The Tau

The tau (symbol: t−) is a charged lepton, similar to the electron, but with much more mass. Since the tau's interactions are very similar to those of the electron, a tau can be thought of as an ustable, heavier version of the electron. Of the charged leptons, the tau is the most massive. The tau is extremely unstable and decays rapidly, with a lifetime of a mere 300 fs (1fs = 10-15 of a second).

The tau is part of the third generation of matter, has an electric charge of -1 e and a bare mass of 1776.8 MeV/c². Like all leptons, the tau is a fundamental fermion with spin 1⁄2. As a charged lepton, the tau experiences three of the four fundamental interactions: gravitation, electromagnetism, and the weak force.

The antiparticle of the tau is called the antitau which differs from the tau only in that its electrical charge and some other properties have equal magnitude but opposite sign. Taus are denoted by t− and antitaus by t+. Like all charged leptons, the tau is associated with a neutrino (non-charged/neutral lepton), the tau neutrino. Tau neutrinos are denoted by νt.

History

The tau was detected in a series of experiments between 1974 and 1977 by Martin Lewis Perl and his colleagues at the SLAC-LBL group. Their equipment could detect and distinguish between leptons, hadrons and photons. They did not detect the tau directly, but rather discovered anomalous events for which there was no conventional explanation. It was proposed that these events occurred due to the production and subsequent decay of a new particle/antiparticle pair (the Tau and the Antitau) This was difficult to verify, because of the amount of energy required to produce the τ+τ− pair, however work done at DESY-Hamburg with the Direct Electron Counter (DELCO) at SPEAR eventually established the mass and spin of the tau.

Tau Neutrino

Tau Neutrino Stats

  • Symbol: νt
  • Generation: Third
  • Type: Neutral
  • Antiparticle: Tau Antineutrino
  • Mass: <15.5 MeV/c²
  • Charge: None
  • Antiparticle Charge: None
  • Colors: None
  • Lifetime: ?

The Tau Neutrino

The tau neutrino (symbol: νt) is the most massive of the neutrinos (which doesn't say much because they are all extremely small). Tau neutrino interactions, or interactions in which tau neutrinos are produced, are not common in the relatively low-energy world we experience in everyday life, but have been measured as the products of high-energy reactions in particle accelerators.

The tau neutrino is part of the third generation of matter, and has an estimated bare mass of <15.5 MeV/c². Like all leptons, the tau neutrino is a fundamental fermion with spin-1⁄2. Being a neutrino, the tau neutrino experiences only two of the four fundamental interactions: gravitation, and the weak force. Tau Neutrinos do not participate with the electromagnetic force and therefore have no electric charge.

The antiparticle of the tau neutrino is the tau antineutrino, which differs from the tau neutrino only in that some of its properties have equal magnitude but opposite sign.

History

The existence of the Tau Neutrino was immediately implied after the tau particle was detected in a series of experiments between 1974 and 1977 by Martin Lewis Perl with his colleagues at the SLAC–LBL group. The discovery of the tau neutrino was announced in July 2000 by the DONUT collaboration. Tau Neutrinos are extremely rare and hard to detect because of the extraordinarily short lifetime of tau particles.