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 $\gamma$, $n$, $p$ and $\beta^\pm$ 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: $\tau({ ^{ 12}\rm{ C}}\to{ ^{ 12}\widetilde{ \rm{ C}}}+\gamma) \geq 5.0\cdot10^{ 31}$ y, $\tau({ ^{ 12}\rm{ C}}\to{ ^{ 11}\widetilde{ \rm{ B}}}+ p) \geq 8.9\cdot10^{ 29}$ y, $\tau({ ^{ 12}\rm{ C}}\to{ ^{ 11}\widetilde{ \rm{ C}}}+ n) \geq 3.4 \cdot 10^{ 30}$ y, $\tau({ ^{ 12}\rm{ C}}\to{ ^{ 12}\widetilde{ \rm{ N}}}+ e^- + \widetilde{ \nu_e}) \geq 3.1\cdot 10^{ 30}$ y and $\tau({ ^{ 12}\rm{ C}}\to{ ^{ 12}\widetilde{ \rm{ B}}}+ e^+ + \nu_e) \geq 2.1 \cdot 10^{ 30}$ 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: $\delta^2_{ \gamma} \leq 2.2\cdot10^{ -57}$, $\delta^2_{ N} \leq 4.1\cdot10^{ -60}$ and $\delta^2_{ \beta} \leq 2.1\cdot10^{ -35}$.
Categories: hep-ex