page_title: Neutrino
hierarchical_section_title: Neutrino
caption_attribution_description: English: The first use of a hydrogen bubble chamber to detect neutrinos, on November 13, 1970. A neutrino hit a proton in a hydrogen atom. The collision occurred at the point where three tracks emanate on the right of the photograph. Français&#160;: Photographie historique de la première observation d'un neutrino dans une chambre à bulles d'hydrogène de 12 pieds (3,70 m.) du Zero Gradient Synchrotron, prise le 13 novembre 1970. Sur cette image, un neutrino invisible percute un proton, donnant naissance aux traces des particules résultant de la collision sur la droite de l'image&#160;: le neutrino se transforme en méson-mu (nom moderne: muon / lepton mu) (longue trace rectiligne centrale). La trace la plus courte au-dessus matérialise le chemin parcouru par le proton. La troisième trace est celle d'un méson-pi créé par la collision.
context_page_description: A neutrino is a fermion that interacts only via the weak subatomic force and gravity. The neutrino is so named because it is electrically neutral and because its rest mass is so small that it was long thought to be zero. The mass of the neutrino is much smaller than that of the other known elementary particles. The weak force has a very short range, the gravitational interaction is extremely weak, and neutrinos do not participate in the strong interaction. Thus, neutrinos typically pass through normal matter unimpeded and undetected.
  Weak interactions create neutrinos in one of three leptonic flavors: electron neutrinos, muon neutrinos, or tau neutrinos, in association with the corresponding charged lepton. Although neutrinos were long believed to be massless, it is now known that there are three discrete neutrino masses with different tiny values, but they do not correspond uniquely to the three flavors. A neutrino created with a specific flavor has an associated specific quantum superposition of all three mass states. As a result, neutrinos oscillate between different flavors in flight.
context_section_description: A neutrino (/nuːˈtriːnoʊ/ or /njuːˈtriːnoʊ/) (denoted by the Greek letter ν) is a fermion (an elementary particle with spin of ) that interacts only via the weak subatomic force and gravity. The neutrino is so named because it is electrically neutral and because its rest mass is so small (-ino) that it was long thought to be zero. The mass of the neutrino is much smaller than that of the other known elementary particles. The weak force has a very short range, the gravitational interaction is extremely weak, and neutrinos do not participate in the strong interaction. Thus, neutrinos typically pass through normal matter unimpeded and undetected.
  Weak interactions create neutrinos in one of three leptonic flavors: electron neutrinos (
  ν
  ₑ), muon neutrinos (
  ν
  μ), or tau neutrinos (
  ν
  τ), in association with the corresponding charged lepton. Although neutrinos were long believed to be massless, it is now known that there are three discrete neutrino masses with different tiny values, but they do not correspond uniquely to the three flavors. A neutrino created with a specific flavor has an associated specific quantum superposition of all three mass states. As a result, neutrinos oscillate between different flavors in flight. For example, an electron neutrino produced in a beta decay reaction may interact in a distant detector as a muon or tau neutrino. Although only differences between squares of the three mass values are known as of 2019, cosmological observations imply that the sum of the three masses must be less than one millionth that of the electron.
  For each neutrino, there also exists a corresponding antiparticle, called an antineutrino, which also has spin of  and no electric charge. Antineutrinos are distinguished from the neutrinos by having opposite signs of lepton number and right-handed instead of left-handed chirality. To conserve total lepton number (in nuclear beta decay), electron neutrinos only appear together with positrons (anti-electrons) or electron-antineutrinos, whereas electron antineutrinos only appear with electrons or electron neutrinos.
  Neutrinos are created by various radioactive decays; the following list is not exhaustive, but includes some of those processes:
  beta decay of atomic nuclei or hadrons,
  natural nuclear reactions such as those that take place in the core of a star
  artificial nuclear reactions in nuclear reactors, nuclear bombs, or particle accelerators
  during a supernova
  during the spin-down of a neutron star
  when cosmic rays or accelerated particle beams strike atoms.
  The majority of neutrinos which are detected about the Earth are from nuclear reactions inside the Sun. At the surface of the Earth, the flux is about 65 billion (6.5×10¹⁰) solar neutrinos, per second per square centimeter. Neutrinos can be used for tomography of the interior of the earth.
  Research is intense in the hunt to elucidate the essential nature of neutrinos, with aspirations of finding:
  the three neutrino mass values
  the degree of CP violation in the leptonic sector (which may lead to leptogenesis)
  evidence of physics which might break the Standard Model of particle physics, such as neutrinoless double beta decay, which would be evidence for violation of lepton number conservation.
caption: The first use of a hydrogen bubble chamber to detect neutrinos, on 13 November 1970, at Argonne National Laboratory. Here a neutrino hits a proton in a hydrogen atom; the collision occurs at the point where three tracks emanate on the right of the photograph.
exif: {}