2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/177712The Pauli exclusion principle (PEP) has been tested for nucleons ($n,p$) in $^{12}C$ and $^{16}O$ 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 $γ$, $n$, $p$ and/or $α$'s emitted in a non-Paulian transition of 1$P$- shell nucleons to the filled 1$S_{1/2}$ shell in nuclei. Similarly, the Pauli-forbidden $β^{\pm}$ 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: $τ(^{12}C\to^{12}\widetilde{C}+γ) > 2.1\cdot10^{27}$ y, $τ(^{12}C\to^{11}\widetilde{B}+ p) > 5.0\cdot10^{26}$ y, $τ(^{12}C(^{16}O)\to^{11}\widetilde{C}(^{15}\widetilde{O})+ n) > 3.7 \cdot 10^{26}$ y, $τ(^{12}C\to^{8}\widetilde{Be}+α) > 6.1 \cdot 10^{23}$ y, $τ(^{12}C\to^{12}\widetilde{N}+ e^- + \widetilde{ν_e})> 7.6 \cdot 10^{27}$ y and $τ(^{12}C\to^{12}\widetilde{B}+ e^+ + ν_e)> 7.7 \cdot 10^{27}$ y, all at 90% C.L.10 pages, 5 figures. Submitted to European Physical Journal C Spokesperson of the Borexino Collaboration: G.Bellini. Corresponding authors: A.Derbin, O.SmirnovHigh Energy Physics - Phenomenologytext