Search for triple and quadruple beta decay of $^{150}$Nd using low-background HPGe detector
Résumé
Triple beta decay of $^{150}$Nd to the ground and excited states of $^{150}$Eu and quadruple beta decay of $^{150}$Nd to the excited states of $^{150}$Gd have been studied using a 400 cm$^3$ low-background HPGe detector. A half-life limit for the quadruple beta decay to the 0$^+_1$ state of $^{150}$Gd was found to be T$_{1/2}$(0$\nu$ + 4$\nu$) > 8.7 × 10$^{20}$ yr (90% C.L.). For other (0$\nu$+4$\nu$) transitions to the excited states limits for the first time have been obtained at the level of (6.1 − 9.5) × 10$^{20}$ yr (90% C.L.). We report here also the results for the first search for triple beta decay to the ground and excited final states of $^{150}$Eu, T$_{1/2}$(0$\nu$ + 3$\nu$) > (0.04 − 4.8) × 10$^{20}$ yr (90% C.L.).