The ILC as a natural SUSY discovery machine and precision microscope: From light higgsinos to tests of unification

The requirement of electroweak naturalness in simple supersymmetric models motivates the ex-istence of a cluster of four light higgsinos with mass 100-300 GeV. While such light compressedspectra may be challenging to observe at the LHC, futuree+e−colliders with√s>2mhiggsinowould serve as both a SUSY discovery machine and a precision microscope.We study higgsino pair production signatures at the ILC based on full,Geant4-based simulationof the ILD concept. We examine several benchmark scenarios that may or may not be accessibleto the HL-LHC searches, with mass differences between the higgsino states between 20 and 4GeV. Assuming√s= 500 GeV and 1000 fb−1of integrated luminosity, the individual higgsinomasses can be measured to 1-2% precision in case of the larger mass differences, and still at thelevel of 5% for the smallest mass difference case. The higgsino mass splittings are sensitive to theelectroweak gaugino masses and can allow extraction of gaugino masses to∼3-20% (dependingon the model). Extrapolation of gaugino masses via renormalization group running can test thehypothesis of gaugino mass unification. We also examine a case with natural generalized miragemediation where the unification of gaugino masses at an intermediate scale apparently gives riseto a natural SUSY spectrum somewhat beyond the reach of the HL-LHC