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

TL;DR

This study used the BOREXINO Counting Test Facility to set new, highly sensitive limits on the decay of nucleons into invisible channels, improving constraints on nucleon stability in nuclei.

Contribution

It provides the most stringent experimental bounds to date on nucleon decay into invisible channels using low-background underground detector data.

Findings

Established new lower bounds on nucleon decay lifetimes.

Achieved the most sensitive limits for decay channels into invisible states.

Demonstrated the effectiveness of the CTF detector in rare decay searches.

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 parents $^{12}$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 ton) of the CTF detector, the most stringent (or competitive) up-to-date experimental bounds have been established: $\tau(n \to inv) > 1.8 \cdot 10^{25}$ y, $\tau(p \to inv) > 1.1 \cdot 10^{26}$ y, $\tau(nn \to inv) > 4.9 \cdot 10^{25}$ y and $\tau(pp \to inv) > 5.0 \cdot 10^{25}$ y, all at 90% C.L.