Introduction to intrinsic reference frames of transitional processes on the example of 2-particle decay

In quantum relativistic physics transition processes are considered within special frames of reference which kinematics of processes becomes symmetric in certain respects. For elastic processes the list of convenient frames of reference is well known. For inelastic ones this list can be supplemented. We propose a general procedure of introducing Lorentz frames of reference for arbitrary processes. As an example we discuss the relativistic kinematics of a two-body decay in different frames of reference among which we distinguish a frame that we call a proper one for the process considered in the whole. The formulas obtained are useful for treatment of weak electromagnetic processes involving heavy quarks such as hyperon decays and more complicated hadron reactions. (author)