Reconstructing the Chargino System at $e^+e^-$ Linear Colliders

Abstract

In most supersymmetric theories charginos, $\tilde{\chi}^\pm_{1,2}$, belong to the class of the lightest supersymmetric particles. The chargino system can be reconstructed completely in $e^+e^-$ collider experiments: $e^+e^-\to\tilde{\chi}_i^+ \tilde{\chi}_j^- [i,j=1,2]$. By measuring the total cross sections and the asymmetries with polarized beams, the chargino masses and the gaugino-higgsino mixing angles of these states can be determined accurately. If only the lightest charginos $\tilde{\chi}_1^\pm$ are kinematically accessible in a first phase of the machine, transverse beam polarization or the measurement of chargino polarization in the final state is needed to determine the mixing angles. From these observables the fundamental SUSY parameters can be derived: the SU(2) gaugino mass $M_2$, the modulus and the cosine of the CP-violating phase of the higgsino mass parameter $\mu$, and $\tan\beta = v_2/v_1$, the ratio of the vacuum expectation values of the two neutral Higgs doublet fields. The remaining two-fold ambiguity of the phase can be resolved by measuring the normal polarization of the charginos. Sum rules of the cross sections can be exploited to investigate the closure of the two-chargino system.