The LHC higgsino discovery plane for present and future SUSY searches

TL;DR

This paper analyzes the higgsino discovery potential at the LHC within natural SUSY models, focusing on the mass discovery plane and naturalness considerations to guide future searches.

Contribution

It provides a detailed theoretical examination of the higgsino discovery plane in various SUSY models, incorporating naturalness criteria to identify promising search regions.

Findings

Electroweak naturalness allows for 4-20 GeV mass gaps.

Stringy naturalness favors smaller 4-10 GeV gaps.

Very small gaps require large gaugino masses, making the scenario unnatural.

Abstract

Considerations from electroweak naturalness and stringy naturalness imply a little hierarchy in supersymmetric models where the superpotential higgsino mass parameter mu is of order the weak scale whilst the soft SUSY breaking terms may be in the (multi-) TeV range. In such a case, discovery of SUSY at LHC may be most likely in the higgsino pair production channel. Indeed, ATLAS and CMS are performing searches in the higgsino mass discovery plane of m(chi_2^0) vs. \Delta m^0 = m(chi_2^0)-m(chi_1^0). We examine several theoretical aspects of this discovery plane in both the gravity-mediation NUHM2 model and the general mirage-mediation (GMM') models. These include: the associated chargino mass m(chi_1^+), the expected regions of the bottom-up notion of electroweak naturalness \Delta_{EW}, and the expected regions of stringy naturalness. While compatibility with electroweak naturalness allows for mass gaps \Delta m^0~ 4-20 GeV, stringy naturalness exhibits a clear preference for yet smaller mass gaps of 4-10 GeV. For still smaller mass gaps, the plane becomes sharply unnatural since very large gaugino masses are required. This study informs the most promising SUSY search channels and parameter space regions for the upcoming HL-LHC runs and possible HE-LHC option.