New limits on nucleon decays into invisible channels with the BOREXINO Counting Test Facility

Abstract The results of background measurements with the second version of the BOREXINO Counting Test Facility (CTF-II), installed in the Gran Sasso Underground Laboratory, were used to obtain limits on the instability of nucleons, bounded in nuclei, for decays into invisible channels ( inv ): disappearance, decays to neutrinos, etc. The approach consisted of a search for decays of unstable nuclides resulting from N and NN decays of parent 12 C, 13 C and 16 O nuclei in the liquid scintillator and the water shield of the CTF. Due to the extremely low background and the large mass (4.2 t) of the CTF detector, the most stringent (or competitive) up-to-date experimental bounds have been established: τ ( n → inv )>1.8×10 25  yr, τ ( p → inv )>1.1×10 26  yr, τ ( nn → inv )>4.9×10 25  yr and τ ( pp → inv )>5.0×10 25  yr, all at 90% C.L.