New experimental limits on violations of the Pauli exclusion principle obtained with the Borexino Counting Test Facility

Abstract.

The Pauli exclusion principle (PEP) has been tested for nucleons (n,p) in ${}^{12}{\rm C}$ and ${}^{16}{\rm O}$ nuclei, using the results of background measurements with the prototype of the Borexino detector, the Counting Test Facility (CTF). The approach consisted of a search for $\gamma$, n, p and/or $\alpha$’s emitted in a non-Paulian transition of 1P- shell nucleons to the filled 1S _1/2 shell in nuclei. Similarly, the Pauli-forbidden $\beta^{\pm}$ decay processes were searched for. Due to the extremely low background and the large mass (4.2 tons) of the CTF detector, the following most stringent up-to-date experimental bounds on PEP violating transitions of nucleons have been established: $\tau({}^{12}{\rm C} \rightarrow {}^{12}{\rm\widetilde C} + \gamma) > 2.1\cdot10^{27} \mathrm y$, $\tau({}^{12}{\rm C} \rightarrow {}^{11}{\rm\widetilde B} + p) > 5.0\cdot10^{26} {\mathrm{y}}$, $\tau({}^{12}{\rm C} ({}^{16}{\rm O}) \rightarrow {}^{11}{\rm\widetilde C} ({}^{15}{\rm\widetilde O} ) + n) > 3.7 \cdot 10^{26} {\mathrm{y}}$, $\tau({}^{12}{\rm C} \rightarrow {}^{8}{\rm\widetilde{Be}} + \alpha) > 6.1 \cdot 10^{23} \mathrm y$, $\tau({}^{12}{\rm C} \rightarrow {}^{12}{\rm\widetilde N} + e^- + \widetilde{\nu_e}) > 7.6 \cdot 10^{27} \mathrm y$ and $\tau({}^{12}{\rm C} \rightarrow {}^{12}{\rm\widetilde B} + e^ + + \nu_e) > 7.7 \cdot 10^{27} \mathrm y$, all at $90 \%$ C.L.