# Test of the Pauli Exclusion Principle in the VIP-2 underground experiment

## TL;DR

The VIP-2 experiment tests the Pauli Exclusion Principle for electrons by searching for forbidden x-ray transitions in copper, setting a new, more stringent limit on possible violations and aiming for further improvements.

## Contribution

This paper reports the first results from the VIP-2 experiment, improving the limit on Pauli Exclusion Principle violations for electrons beyond previous bounds.

## Key findings

- New limit on violation probability: 4.7 × 10^{-29}
- Improved sensitivity over VIP experiment
- Progress towards two orders of magnitude better constraints

## Abstract

The validity of the Pauli Exclusion Principle, a building block of Quantum Mechanics, is tested for electrons. The VIP (VIolation of Pauli exclusion principle) and its follow-up VIP-2 experiments at the Laboratori Nazionali del Gran Sasso search for x-rays from copper atomic transition that are prohibited by the Pauli Exclusion Principle. The candidate events, if they exist, originate from the transition of a $2p$ orbit electron to the ground state which is already occupied by two electrons. The present limit on the probability for Pauli Exclusion Principle violation for electrons set by the VIP experiment is 4.7 $\times$ 10 $^{-29}$. We report a first result from the VIP-2 experiment improving on the VIP limit, that solidifies the final goal to achieve a two order of magnitude gain in the long run.