Two-Electron Atoms — Pauli Principle

Frederick Reines, Henry W. Sobel

Jim Baggott

Despite the success of Schrödinger’s description of the H-atom, it became apparent that the spectrum of the simplest multi-electron atom—helium—could not be so readily explained. And the spectra of other atoms showed ‘anomalous’ splitting in a magnetic field. In 1920 Sommerfeld introduced a fourth quantum number. A few years later Pauli was led to the inspired conclusion that the electron must have a curious ‘two-valuedness’ characterized by a quantum number of ½, and went on to discover the exclusion principle. Perhaps this is because the electron possesses a self-rotation, leading to the notion of electron spin, potentially explaining why each orbital can accommodate only two electrons. Heisenberg traced this behaviour back to the symmetry properties of the wavefunctions. By observing which transitions in the spectrum of helium are allowed and which are forbidden, we can deduce the generalized Pauli principle, from which the exclusion principle follows.

J. Marton, A. Pichler, Aidin Amirkhani +25 more

Abstract The VIP2 (VIolation of the Pauli Exclusion Principle) experiment at the Gran Sasso underground laboratory (LNGS) is searching for possible violations of standard quantum mechanics predictions in atoms at very high sensitivity. We investigate atomic transitions with precision X-ray spectroscopy in order to test the Pauli Exclusion Principle (PEP) and therefore the related spin-statistics theorem. We will present our experimental method for the search for “anomalous” (i.e. Pauli-forbidden) X-ray transitions in copper atoms, produced by “new” electrons, which could have tiny probability to undergo Pauli-forbidden transition to the ground state already occupied by two electrons. We will describe the VIP2 experimental setup, which is taking data at LNGS presently. The goal of VIP2 is to test the PEP for electrons with unprecedented accuracy, down to a limit in the probability that PEP is violated at the level of 10−31. We will present current experimental results and discuss implications of a possible violation.

Catalina Curceanu, Hexi Shi, Sergio Bartalucci +25 more

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 transitions that are prohibited by the Pauli exclusion principle. The candidate events—if they exist—originate from the transition of a 2 p 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 × 10 − 29 . We report a first result from the VIP-2 experiment improving on the VIP limit, which solidifies the final goal of achieving a two orders of magnitude gain in the long run.