Sneutrino cascade decays ~nu_e -> e- ~X_1^+ -> e- f f' ~X_1^0 as a probe of chargino spin properties and CP violation

Abstract

The decays ~nu_e -> e- ~X_1^+, ~nu_e* -> e+ ~X_1^-, when kinematically allowed, constitute a source of 100% polarised charginos. We study the process e+ e- -> ~nu_e* ~nu_e -> e+ ~X_1^- e- ~X_1^+, with subsequent chargino decays \~X_1^- -> nu_mu mu- ~X_1^0, X_1^+ -> q qbar' ~X_1^0 or their charge conjugate \~X_1^- -> qbar q' ~X_1^0, ~X_1^+ -> nu_mu mu+ ~X_1^0. 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 ~X_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 M_1 and can test CP violation in the neutralino sector.