Pauli Exclusion Principle test with electrons at LNGS

According to our present understanding, nature is divided according to the Spin-Statistic connection into bosons and fermions. The Pauli Exclusion Principle (PEP) is a consequence of the Spin-Statistics connection and prevents two fermions, like electrons, from being in the same quantum state. Consequently, quantum states with two electrons in the same state are forbidden. Therefore, the PEP is a pillar of our understanding of nature. It helps to explain interesting phenomena like the periodic table of elements and also exotic objects such as neutron stars. An intuitive explanation of the Pauli Exclusion Principle is still missing. Speculations about a possible violation are existing in literature. Thus, it is extremely important to experimentally test its validity with high sensitivity. So far, no experiment has found a violation of the PEP. Nevertheless, the experiments succeeded to put increasingly tight upper bounds on the probability for its violation. The VIP (Violation of the Pauli Principle) experiment could establish the most stringent bounds up to now. Its successor experiment VIP2 is presently taking data at the Gran Sasso Underground Laboratory (LNGS) in Italy. It tests the violation of the PEP in atomic transitions of electrons with strongly increased sensitivity compared to the VIP experiment. It searches for X-rays coming from atomic transitions forbidden by the PEP. We propose an upgrade to this experiment. On the one hand the upgrade consists of new detectors with a larger detector area. This increases the probability to detect the forbidden X-rays from PEP violating atoms. On the other hand we will install an optimized shielding of the experiment against radiation originating from the environment at the LNGS experiment site. These improvements will enable us to test the PEP with unprecedented sensitivity.

The VIP2 experiment is conducted in the italian Underground-Laboratory LNGS (Laboratori Nazionali di Gran Sasso) of INFN (Istituto Nazionali di Fysika Nucleare). The experiment reached the up-to-now most stringent limit for apossible violation of the Pauli Exclusion Principle (PEP) for elektrons with the search for forbidden atomic transitions in the Roentgen energy range using Silicon-Drift-Detektors. New methods concerning data analysis applying the Bayes concept were developed and used with the measured data. The experiment could verify the validity of the Pauli Exclusioin Principle. An extremely important result is the test of theoretical models in quantum gravity due to the extreme sensitivity of the VIP2 experiment. A publication on this topic was published 2022 in the journal Physical Review Letters.