A Nondiagonal Pair of Majorana Particles at $e^+e^-$ Colliders

Abstract: We perform a comprehensive and model-independent analysis for characterizing the spin and dynamical structure of the production of a non-diagonal pair of Majorana particles with different masses and arbitrary spins, $e^{-e^+\to} X_2 X_1$, followed by a sequential two-body decay, $X_2\to Z X_1$, of the heavier particle $X_2$ into a $Z$ gauge boson and the lighter particle $X_1$ escaping undetected at high-energy $e<sup>+e<sup>-$ colliders. Standard leptonic $Z$-boson decays, $Z\to \ell<sup>-\ell<sup>+$ with $\ell=e$ or $\mu$, are employed for precisely diagnosing the $Z$ polarization influenced by the production and decay processes. Based on helicity formalism and Wick helicity rotation for describing the correlated production-decay amplitudes and distributions, we work out the implications on the amplitudes and distributions of discrete CP symmetry and the Majorana condition that two particles are their own anti-particles. For the sake of a concrete illustration, an example of this type in the minimal supersymmetric Standard Model is investigated in detail.