Muons were discovered in 1936 by Carl Anderson and Seth Neddermeyer, who were performing experiments with cosmic rays from deep space (Anderson had already discovered the electron's anti-particle, the positron, four years earlier). (Image credit: Photo12/Universal Images Group via Getty Images) He is photographed here in the Cavendish Laboratory, Cambridge, UK. Many chemical processes are related to the presence of these electrons in atoms.īritish physicist Joseph John Thomson discovered the electron in 1897. Positive charges on the protons and the negative charges on the electrons cancel out to create an electrically neutral atom. An atom will have the same number of electrons as it does protons, ensuring that the Electrons are important components of atoms, orbiting the nucleus of an atom composed of protons and neutrons. An electron has a rest mass energy of 0.511 MeV (Mega electron-Volt) (which equates to 9.1 x 10^–31 kilograms). The electron was the first lepton to be discovered, in 1897 by the British physicist Joseph John Thomson. It turned out that they weren't vanishing, but oscillating into muon and tau neutrinos on their way here. Neutrino oscillations are the solution to the mystery of the solar neutrino problem, where it seemed that only a third of the expected number of electron neutrinos from the sun were reaching Earth. This is referred to as neutrino oscillation and is described by physicists in Stanford University's Neutrino Group. 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. So, a neutron could never decay and produce an electron and an anti-muon neutrino, because they belong to different families of leptons. The Lepton Number of an electron is 1, and the Lepton Number of an anti-neutrino is –1, hence they cancel and conserve the overall Lepton Number of the reaction.Ĭomplicating things are the three families of leptons (electron and electron neutrinos, muons and muon neutrinos, and tau particles and tau neutrinos) and the rules of Lepton Numbers say they can't be mixed and matched. Therefore its decay products must also add up to a Lepton Number of 0. A neutron is a baryon, not a lepton, so its Lepton Number is 0. First of all, it conserves a property known as the Lepton Number, which is defined by physicists at Georgia State University as the number of leptons minus the number of anti-leptons. This decay reaction demonstrates a couple of the fundamental properties of leptons. Tachyons: Facts about these faster-than-light particles Leptons and their corresponding neutrinos have a lepton number of 1, while antileptons and lepton antineutrinos have a lepton number of -1.- Higgs boson: The 'God Particle' explained A quantum number can only take integer values.Īll quarks have a baryon number of \dfrac\right). This means that in a particle interaction, both sides of the equation must have the same baryon number. The baryon number is a quantum number and is conserved for all particle interactions. Baryons have a baryon number of B = 1, antibaryons have a baryon number of B = -1, with all other particles having a baryon number of B = 0. There are other types of baryons, including sigmas \left(\Sigma\right) and lambdas \left(\Lambda\right), but these have very short half-lives and you don’t need to know them.Īll particles have a baryon number \left(B\right). The quarks are all the same type of quark either 3 normal quarks (baryon) or 3 antiquarks (antibaryon).
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