Research on the phase space of three- and four-body final states processes

Analytical formulae for the phase space factors and three-momenta of three- and four-body final states are derived for all sets of independent kinematic variables containing invariant mass variables. These formulae will help experimental physicists to perform data analysis. As an example, we show how to use these formulae to distinguish the different mechanisms of the begin{document}$ e+pto e+J/psi+ p $end{document} process when searching the signals of begin{document}$ P_c $end{document} states in the energy region of the Electron–Ion collider at China (EicC).