New experimental limits on the Pauli forbidden transitions in $^{12}$C nuclei obtained with 485 days Borexino data

Abstract

The Pauli exclusion principle (PEP) has been tested for nucleons ($n,p$) in $^{12}C$ with the Borexino detector.The approach consists of a search for $γ$, $n$, $p$ and $β^\pm$ emitted in a non-Paulian transition of 1$P_{3/2}$- shell nucleons to the filled 1$S_{1/2}$ shell in nuclei. Due to the extremely low background and the large mass (278 t) of the Borexino detector, the following most stringent up-to-date experimental bounds on PEP violating transitions of nucleons have been established: $τ({^{12}\rm{C}}\to{^{12}\widetilde{\rm{C}}}+γ) \geq 5.0\cdot10^{31}$ y, $τ({^{12}\rm{C}}\to{^{11}\widetilde{\rm{B}}}+ p) \geq 8.9\cdot10^{29}$ y, $τ({^{12}\rm{C}}\to{^{11}\widetilde{\rm{C}}}+ n) \geq 3.4 \cdot 10^{30}$ y, $τ({^{12}\rm{C}}\to{^{12}\widetilde{\rm{N}}}+ e^- + \widetilde{ν_e}) \geq 3.1\cdot 10^{30}$ y and $τ({^{12}\rm{C}}\to{^{12}\widetilde{\rm{B}}}+ e^+ + ν_e) \geq 2.1 \cdot 10^{30}$ y, all at 90% C.L. The corresponding upper limits on the relative strengths for the searched non-Paulian electromagnetic, strong and weak transitions have been estimated: $δ^2_γ \leq 2.2\cdot10^{-57}$, $δ^2_{N} \leq 4.1\cdot10^{-60}$ and $δ^2_β \leq 2.1\cdot10^{-35}$.