Neutralino Production and Decay at an e^+e^- Linear Collider with Transversely Polarized Beams

Abstract

Once supersymmetric neutralinos $\tilde{\chi}^0$ are produced copiously at $e^+e^-$ linear colliders, their characteristics can be measured with high precision. In particular, the fundamental parameters in the gaugino/higgsino sector of the minimal supersymmetric extension of the standard model (MSSM) can be analyzed. Here we focus on the determination of possible CP--odd phases of these parameters. To that end, we exploit the electron/positron beam polarization, including transverse polarization, as well as the spin/angular correlations of the neutralino production $e^+ e^- \to \tilde{\chi}^0_i \tilde{\chi}^0_j$ and subsequent 2--body decays $\tilde{\chi}^0_i \to \tilde{\chi}^0_k h, \tilde{\chi}^0_k Z, \tilde \ell^\pm_R \ell^\mp$, using (partly) optimized CP--odd observables. If no final--state polarizations are measured, the $Z$ and $h$ modes are independent of the $\tilde{\chi}^0_i$ polarization, but CP--odd observables constructed from the leptonic decay mode can help in reconstructing the neutralino sector of the CP--noninvariant MSSM. In this situation, transverse beam polarization does not seem to be particularly useful in probing explicit CP violation in the neutralino sector of the MSSM. This can most easily be accomplished using longitudinal beam polarization.