Neutrino

:Neutrino is also an operating system. See QNX.

Types of neutrinos

There are three known types (flavors) of neutrinos: electron neutrino νe, muon neutrino νμ and tau neutrino ντ, named after their partner leptons in the Standard Model (see table at right). The current best measurement of the number of neutrino types comes form observing the decay of the Z boson. This particle can decay into any neutrino and its antineutrino, and the more types of neutrinos available, the shorted the lifetime of the Z boson. The latest measurements put the number of light neutrino types (where "light" means having mass less than half the Z mass) at 2.984±0.008http://pdg.lbl.gov/2004/listings/lxxx.html. The possibility of sterile neutrinos — neutrinos which do not participate in the weak interaction but which could be created through flavor oscillation (see below) — is unaffected by these Z-boson-based measurements. The correspondence between the six - currently known - quarks in the Standard Model and the six leptons, among them the three neutrinos, provides additional evidence that there should be exactly three types. However, conclusive proof that there are only three kinds of neutrinos remains an elusive goal of particle physics.

Related Topics:
Flavors - Electron - Muon - Tau - Lepton - Standard Model - Z boson - Quarks

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Flavor Oscillations

Neutrinos are always created or detected with a well defined flavor (electron, muon, tau). However, in a phenomenon known as neutrino flavor oscillation, neutrinos are able to oscillate between the three available flavors while they propagate through space. Specifically, this occurs because the neutrino flavor eigenstates are not eigenstates of the propagation Hamiltonian. This allows for a neutrino that was produced as an electron neutrino at a given location to have a calculable probability to be detected as either a muon or tau neutrino after it has traveled to another location. This effect was first noticed due to the number of electron neutrinos detected from the sun's core failing to match the expected numbers, a discrepancy dubbed the "solar neutrino problem". The existence of flavor oscillations implies a non-zero neutrino mass, since the amount of mixing between neutrino flavors is proportional to the differences in their squared-masses (zero for massless neutrinos). Despite their massive nature, it is still possible that the neutrino and antineutrino are in fact the same particle, a hypothesis first proposed by the Italian physicist Ettore Majorana.

Related Topics:
Neutrino flavor oscillation - Eigenstates - Hamiltonian - Solar neutrino problem - Antineutrino - Ettore Majorana

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