Sneutrino cascade decays as a probe of chargino spin properties and CP violation

The decays ν˜e→e−χ˜1+, ν˜e∗→e+χ˜1−, when kinematically allowed, constitute a source of 100% polarised charginos. We study the process e+e−→ν˜e∗ν˜e→e+χ˜1−e−χ˜1+, with subsequent chargino decays χ˜1−→ν¯μμ−χ˜10, χ˜1+→qq¯′χ˜10 or their charge conjugate χ˜1−→q¯q′χ˜10, χ˜1+→νμμ+χ˜10. The kinematics of this process allows the reconstruction of the sneutrino and chargino rest frames, and thus a clean analysis of the angular distributions of the visible final state products in these reference systems. Furthermore, a triple product CP asymmetry can be built in χ˜1± hadronic decays, involving the chargino spins and the momenta of the quark and antiquark. With a good c tagging efficiency, this CP asymmetry is quite sensitive to the phase of the bino mass term M1 and can test CP violation in the neutralino sector.