Pauli Ionization Mechanism for Recoil Atoms in Matter

Free-electron emission by stopping recoil atoms arising from particle-atom collisions in a noblegas medium is numerically investigated using argon as an example. We demonstrate that, during propagation through matter of recoil atoms with energies over a few keV, vacancies in their internal L-shells arise via the Pauli mechanism with a probability on the order of 100%. As a result, over 30 free electrons are released upon a single interaction act in liquid or gaseous noble gas as a working medium of a particle detector. Thereby, the sensitivity of an argon-filled particle detector is significantly enhanced. In a xenon-filled detector, Pauli ionization sets in at higher recoil-atom energies of greater than or similar to 100-200 keV and, therefore, is unlikely to boost the detector sensitivity to light-dark-matter particles, which are generally expected to produce recoil atoms with energies less than or similar to 10 keV.