Normal tau polarization as a sensitive probe of CP violation in chargino decay

CP violation in the spin-spin correlations in chargino production and subsequent two-body decay into a tau and a tau-sneutrino is studied at the ILC. From the normal polarization of the tau, an asymmetry is defined to test the CP-violating phase of the higgsino mass parameter mu. Asymmetries of more than +/- 70% are obtained, also in scenarios with heavy first and second generation sfermions. Bounds on the statistical significances of the CP asymmetries are estimated. As a result, the normal tau polarization in the chargino decay is one of the most sensitive probes to constrain or measure the phase phi(mu) at the ILC, motivating further detailed experimental studies.