– 1 – Searches for Massive Neutrinos

A. Heavy neutral lepton mass limits; B. Sum of neutrino masses; C. Searches for neutrinoless double-β decay (see the note by P. Vogel on “Searches for neutrinoless double-β decay” preceding this section); D. Other bounds from nuclear and particle decays; E. Solar ν experiments (see the note on “Solar Neutrinos” by K. Nakamura preceding this section); F. Astrophysical neutrino observations; G. Reactor νe disappearance experiments; H. Accelerator neutrino appearance experiments; I. Disappearance experiments with accelerator and radioactive source neutrinos. Direct searches for masses of dominantly coupled neutrinos are listed in the appropriate section on νe, νμ, or ντ . Searches for massive charged leptons are given elsewhere, and searches for the mixing of (μ−e+) and (μ+e−) are given in the muon Listings. Discussion of the current neutrino mass limits and the theory of mixing are given in the note on “Neutrino Mass” by Boris Kayser just before the νe Listings. In many of the following Listings (e.g. neutrino disappearance and appearance experiments), results are presented assuming that mixing occurs only between two neutrino species, such as ντ ↔ νe. This assumption is also made for leptonnumber violating mixing between two states, such as νe ↔ νμ or νμ ↔ νμ. As discussed in Kayser’s review, the assumption of mixing between only two states is valid if (a) all mixing angles are small or (b) there is a mass hierarchy such that one ∆M2 ij , e.g. ∆M2 21 = M 2 ν2 −M2 ν1 , is small compared with the others, so that there is a region in L/E (the ratio of the distance L that the neutrino travels to its energy E) where ∆M2 21L/E is negligible, but ∆M2 32L/E is not.