New limits on the Pauli forbidden transitions in nuclei

New limits on the Pauli forbidden transitions in nuclei obtained with the complete Borexino dataset.

Eur. Phys. J. C86, 736 (2026).

Published 30 June 2026

Abstract

The Pauli exclusion principle (PEP) was tested for nucleons in $^{12}{C}$ nuclei using the Borexino dataset from 2007 to 2021. The approach consists of searching for $\gamma$ -quanta, neutrons, protons, as well as electrons and positrons emitted in non-Paulian transitions of nucleons from the $1P_{3/2}$ shell to the filled $1S_{1/2}$ shell. Due to the uniquely low background level, the large mass, and long measurement time of the Borexino detector, the most stringent experimental constraints to date on the lifetime of the $\mathrm {^{12}C}$ nucleus with respect to PEP-forbidden transitions were obtained:

$\tau ({^{12}\textrm{C}}\rightarrow {^{12}\widetilde{\textrm{C}}}+\gamma ) \ge {1.1\times 10^{32}}$ y,
$\tau ({^{12}\textrm{C}}\rightarrow {^{11}\widetilde{\textrm{B}}}+ p) \ge {1.0\times 10^{31}}$ y,
$\tau ({^{12}\textrm{C}}\rightarrow {^{11}\widetilde{\textrm{C}}}+ n) \ge 2.0 \times 10^{31}$ y,
$\tau ({^{12}\textrm{C}}\rightarrow {^{12}\widetilde{\textrm{N}}}+ e^- + \overline{\nu }_e) \ge 6.4 \times 10^{30}$ y and
$\tau ({^{12}\textrm{C}}\rightarrow {^{12}\widetilde{\textrm{B}}}+ e^+ + \nu _e) \ge 6.6 \times 10^{30}$ y

(90% C.L.)

The upper limits on the relative strengths for the non-Paulian electromagnetic, strong, and weak transitions have been obtained: $\delta ^2_{\gamma }\le 1.0\times 10^{-57}$ , $\delta ^2_{N}\le 7.0\times 10^{-61}$ and $\delta ^2_{\beta }\le 9.6\times 10^{-36}$ , all at 90% C.L.

See also:

New limits on the Pauli forbidden transitions in nuclei

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Abstract

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