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 $0\nu \beta \beta$ decay in ${}^{76}\mathrm{Ge}$ of $T_{1/2}^{0\nu }\ge 5.7\times {10}^{25}\mathrm{yr}$ at $90\%$ C.L. (after PDG98 [C. Caso et al., Eur. Phys. J. C3, 1 (1998]), the sensitivity of the experiment being $T_{1/2}^{0\nu }\ge 1.6\times {10}^{25}\mathrm{yr}$ 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.

• Received 26 January 1999

DOI:https://doi.org/10.1103/PhysRevLett.83.41