On 4 December 1930, Austrian theorist Wolfgang Pauli (pictured here in 1933) wrote a famous letter in which he dared to hypothesise the existence of new particle - now known as the neutrino. He proposed the new particle to explain why energy seemed to go missing in the form of radioactivity known as beta-decay. The neutrino would took away energy but without being detected, as it has no electric charge and a very small mass. It was to be another 26 years before Fred Reines and Clyde Cowan claimed the first detection of Pauli's "undetectable" particle. Pauli himself went on to receive the Nobel prize for physics not the neutrino but for his famous "exclusion principle". CERN Pauli Archive Wolfgang Paulifamous letterneutrinoradioactivitybeta-decayFred Reinesthe first detectionexclusion principle

Proposal of neutrino existence, from conservation arguments The first known observation of a neutrino, on November 13, A neutrino hit a proton in a hydrogen bubble chamber. The collision occurred at the point where three tracks emanate on the right of the photograph. The neutrino[nb 1] was first postulated in 1930 by Wolfgang Pauli to preserve the conservation of energy, conservation of momentum, and conservation of angular momentum in beta decay—the decay of an atomic nucleus (not known as neutron back then) into a proton, an electron and an antineutrino.[nb 2][2]bubble chamber[nb 1]Wolfgang Pauli conservation of energyconservation of momentumconservation of angular momentumbeta decayneutronprotonelectron[nb 2][2] n 0 → p + + e − + ν 0

He theorized that an undetected particle was carrying away the observed difference between the energy, momentum, and angular momentum of the initial and final particles.energy momentumangular momentum Pauli originally named his proposed light particle a neutron. When James Chadwick discovered a much more massive nuclear particle in 1932 and also named it a neutron, this left the two particles with the same name. Enrico Fermi, who developed the theory of beta decay, coined the term neutrino in 1934 as a clever way to resolve the confusion. It was a pun on neutrone, the Italian equivalent of neutron.[3]James ChadwickneutronEnrico FermipunItalian[3] [edit] Direct detection from induced beta decayedit

In 1942 Kan-Chang Wang first proposed the use of beta-capture to experimentally detect neutrinos.[4] In 1956 Clyde Cowan, Frederick Reines, F. B. Harrison, H. W. Kruse, and A. D. McGuire detected the neutrino through this process,[5] a result that was rewarded with the 1995 Nobel Prize. In this experiment, now known as the Cowan–Reines neutrino experiment, neutrinos created in a nuclear reactor by beta decay were shot into protons producing neutrons and positrons both of which could be detected. It is now known that both the proposed and the observed particles were antineutrinos.Kan-Chang Wang[4]Clyde CowanFrederick Reines[5]1995 Nobel PrizeCowan–Reines neutrino experimentneutronspositrons

First neutrino observation Nov. 13, 1970in the Zero Gradient Synchrotron's 12-foot H bubble chamber. The invisible neutrino strikes a proton where three particle tracks originate (lower right). The neutrino turns into a mu- meson, the long center track (extending up and left). The short track is the proton. The third track (extending down and left) is a pi-meson created by the collision. Argonne National Laboratory

Neutrinos (Italian pronunciation: [neu ˈ tri ː no], meaning "small neutral one"; English pronunciation: /nju ːˈ tri ː no ʊ /) are elementary particles that often travel close to the speed of light, are electrically neutral, and are able to pass through ordinary matter almost undisturbed and are thus extremely difficult to detect. Neutrinos have a minuscule, but nonzero mass. They are denoted by the Greek letter ν (nu).[neu ˈ tri ː no]/nju ːˈ tri ː no ʊ /elementary particlesspeed of light electrically neutralordinary mattermassnu Neutrinos are created as a result of certain types of radioactive decay or nuclear reactions such as those that take place in the Sun, in nuclear reactors, or when cosmic rays hit atoms. There are three types, or "flavors", of neutrinos: electron neutrinos, muon neutrinos and tauon neutrinos (or tau neutrino); each type also has a corresponding antiparticle, called antineutrinos. Electron neutrinos (or antineutrinos) are generated whenever neutrons change into protons (or protons into neutrons), the two forms of beta decay. Interactions involving neutrinos are mediated by the weak interaction.radioactive decaynuclear reactions Sunnuclear reactorscosmic raysflavorselectron neutrinos muon neutrinostauon neutrinosantiparticleantineutrinos neutronsprotonsbeta decayweak interaction Most neutrinos passing through the Earth emanate from the Sun, and more than 50 trillion solar electron neutrinos pass through the human body every second.[1]trillionsolar electron neutrinos[1]

Neutrino Composition:Elementary particleStatistical behavior:FermionGroup:LeptonInteraction:weak interaction and gravitationSymbol(s):νe, νμ, ντAntiparticle:Antineutrino (νe, νμ, ντ) Antineutrinos are possibly identical to the neutrino (see Majorana fermion).Theorized:νe:Elementary particleStatistical behaviorFermionLeptonInteractionweak interactiongravitationAntiparticleMajorana fermion Wolfgang PauliWolfgang Pauli (1930) νμ: Late 1940s ντ: Mid 1970s Discovered:νe: Clyde Cowan, Frederick Reines (1956) νμ: Leon Lederman, Melvin Schwartz and Jack Steinberger (1962) ντ: DONUT collaboration (2000)Types:3 – electron neutrino, muon neutrino and tauon neutrinoMass:Small, but non-zero. See the mass section.Electric charge:0 eSpin:1⁄2Weak hypercharge:−1B − L:−1X:−3Clyde CowanFrederick ReinesLeon LedermanMelvin Schwartz Jack SteinbergerDONUT collaborationMassmassElectric chargeeSpinWeak hyperchargeB − LX

The first known observation of a neutrino, on November 13, A neutrino hit a proton in a hydrogen bubble chamber. The collision occurred at the point where three tracks emanate on the right of the photograph. Wikibubble chamber