One way to fulfill this rule and test the Pauli exclusion principle with high precision is to introduce "new" electrons in a conductor. The electrons form new quantum states with the atoms in the conductor. These "new" states could violate the Pauli exclusion principle. The aim of VIP2 is to search for new quantum states, which have a symmetric component in an otherwise antisymmetric state. These non-Paulian states can be identified by the characteristic X-rays emitted during Pauli exclusion principle—prohibited atomic transitions to the ground state. An example for a transition of this kind would be a third electron arriving on the 1s level. The emitted X-rays are detected by silicon drift detectors.