New limits on effective Majorana neutrino masses from rare kaon decays

Abstract

The rare kaon decay $K^{+}\text{ra}{\pi }^{-}{\mu }^{+}{\mu }^{+}$ is violating lepton number by two units and is investigated within the context of Majorana neutrino masses. Using a new upper bound for this decay from E865 an upper limit on the effective Majorana mass term ${\text{m}}_{\mu \mu }<500$ GeV could be obtained. This is improving existing bounds by about one order of magnitude. Implications on heavy neutrinos are discusse d as well as future possibilities to improve limits on this as well as other elements of the Majorana m ass matrix are investigated.

Comments: 7 pages, 3 eps-figures, to be published in Phys. Lett. B