Limits on the Majorana Neutrino Mass in the 0.1 eV Range

Abstract

The Heidelberg-Moscow experiment gives the most stringent limit on the Majorana neutrino mass. After 24 kg yr of data with pulse shape measurements, we set a lower limit on the half-life of the $0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$ decay in ${}^{76}\mathrm{Ge}$ of ${T}_{1/2}^{0\ensuremath{\nu}}\ensuremath{\ge}5.7\ifmmode\times\else\texttimes\fi{}{10}^{25}\mathrm{yr}$ at $90%$ C.L. (after PDG98 [C. Caso et al., Eur. Phys. J. C3, 1 (1998]), the sensitivity of the experiment being ${T}_{1/2}^{0\ensuremath{\nu}}\ensuremath{\ge}1.6\ifmmode\times\else\texttimes\fi{}{10}^{25}\mathrm{yr}$ at $90%$ C.L. We thus exclude an effective Majorana neutrino mass greater than 0.2 eV (0.39 eV sensitivity), using the matrix elements of A. Staudt, K. Muto, and H. V. Klapdor-Kleingrothaus, Europhys. Lett. 13, 31 (1990). This limit sets strong constraints on degenerate neutrino mass models.