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Abstract

The Pauli Exclusion Principle (PEP) appears from fundamental symmetries in quantum field theories, but its physical origin is still to be understood. High-precision experimental searches for small PEP violations permit test- ing key assumptions of the Standard Model with high sensi- tivity. We report on a dedicated measurement with Gator, a low-background, high-purity germanium detector operated at the Laboratori Nazionali del Gran Sasso, aimed at test- ing PEP-violating atomic transitions in lead. The experi- mental technique, relying on forming a new symmetry state by introducing electrons into the pre-existing electron sys- tem through a direct current, satisfies the conditions of the Messiah-Greenberg superselection rule. No PEP violation has been observed, and an upper limit on the PEP violation probability of β²/2 < 4.8 x 10⁻²⁹ (90% CL) is set. This improves the previous constraint from a comparable mea- surement by more than one order of magnitude.