On the probability of finding and momentum of a free particle from another free particles point of view

In this Note it is investigated, which probability of finding and probability of momentum of a free particle with mass m2 is perceived from another free particles point of view with mass m1. Both particles are distinguishable. An example is given for a non-relativistic case, to show which quantum mechanic wave functions (space and momentum) describe the particle with mass m2 from the other particles point of view. The uncertainty relation for this special case is given. A limiting case is considered, when the perceiving particle is a laboratory system with m1>>m2 . In a short outlook the approach in the relativistic case is considered.