Twoneutrino

Twoneutrino is not a standard term in particle physics. In most contexts, it refers informally to two-neutrino processes, especially the two-neutrino double beta decay (2νββ). There is no particle or interaction officially named twoneutrino.

Two-neutrino double beta decay is a second-order weak process in certain even-even nuclei where the nuclear state changes by two units of charge with the emission of two electrons and two (anti)neutrinos. It is allowed in the Standard Model and conserves lepton number. The energy spectrum of the emitted electrons and the total decay rate depend on nuclear matrix elements and phase space factors, making precise predictions challenging.

Experimentally, 2νββ has been observed in multiple isotopes, with half-lives typically in the range of 10^18 to 10^21 years. Measurements test nuclear theory and provide backgrounds for neutrinoless double beta decay searches. Distinguishing 2νββ from 0νββ relies on the energy sum of the electrons: 2νββ produces a continuous spectrum, whereas 0νββ would yield a peak near the Q-value if neutrinos are Majorana particles.

While the term twoneutrino is not standard, it is sometimes used informally when discussing two-neutrino processes in double beta decay, or as shorthand for the broader class of two-neutrino interactions. The concept is important for understanding lepton-number conservation, neutrino masses, and the potential for physics beyond the Standard Model.