Analytical formula (see text) vs. numerical simulation of the density distribution of the product , where r_p is the distance between pair members projected on the plane of the sky and v_z is their radial velocity difference. This combination of variable is essential for the statistical determination of the total mass of the pair. The product is plotted here for r = 1 and v = 1, i.e., the plotted variable is actually . The number of simulated pairs is N ≈ 10 000. Within statistical fluctuations, the obtained probability distribution agrees well with the theoretical expectation (red line, Eq. (20)).