The Pauli Exclusion Principle (PEP) represents one of the fundamental principles of the modern physics and all our comprehension of the surrounding matter is based on it. Even if today there are no compelling reasons to doubt its validity, it still spurs a lively debate on its limits, as testified by the abundant contributions found in the literature and in topical conferences.

It is clear that part of the interest towards these very important fundamental principles is due to their evasiveness. Feynman wrote [17]:

“ This brings up an interesting question: Why is it that particles with half-integral spin are Fermi particles (...) whereas particles with integral spin are Bose particles (...)? We apologize for the fact that we can not give you an elementary explanation. An explanation has been worked out by Pauli from complicated arguments from quantum field theory and relativity. He has shown that the two must necessarily go together, but we have not been able to find a way to reproduce his arguments on an elementary level. It appears to be one of the few places in physics where there is a rule which can be stated very simply, but for which no one has found a simple and easy explanation. (...) This probably means that we do not have a complete understanding of the fundamental principle involved. For the moment, you will just have to take it as one of the rules of the world.”

The VIP experiment aims to improve the current limit on the violation of the Pauli principle for electrons, (P<1.7 x 10 -26 ), reported in E. Ramberg e G. A. Snow: Experimental limit on a small violation of the Pauli principle , Phys. Lett. B 238 (1990) 438 , by four orders of magnitude (P< 10 -30 ), exploring a region where new theories allow for a possible PEP violation.