Detection of massive multi-particle beams by two-particle ionization

Multi-photon absorption is a well-known phenomenon. With atom lasers a similar process could take place for massive particles, the ionization of an atom or molecule by the successive interaction with various particles. This process would lead to multi-particle detection events for incident multi-particle beams. We show that two-particle detections would introduce a correction (proportional to the fourth power of the wavefunction modulus) to the usual one-particle detection probability (only proportional to the second power).