Hale Sert (DESY)
In unconstrained SUSY models, the most natural value for the mu parameter is not far from the Z^0 mass, predicting the lightest gauginos to be higgsino-like and nearly degenerate in mass, with mass splittings of a few GeV or even of less than a GeV. At the ILC, chi_1^0 chi_2^0 and chi_1^+ chi_1^- production can be detected via the recoil against hard photon radiation and even sub-GeV mass differences can be reconstructed from the kinematics of the very soft visible decay products. The expected precisions on the polarised cross sections, on the chi_1^+- and chi_2^0 masses and on their mass differences to the chi_1^0 have been investigated with the ILD detector concept at the centre-of-mass energies of 350 and 500 GeV, taking into account realistic assumptions on the beam parameters and beam-induced backgrounds. From these observables alone, the mu parameter can be determined to the level of a few percent, while M_1 and M_2 can be constrained within 10-20% even if they are in the multi-TeV regime.