Naturalness and light higgsinos: A powerful reason to build the ILC

TL;DR

The paper argues that the proposed International Linear Collider offers a promising environment to detect or exclude light higgsinos predicted by natural Supersymmetry, which are difficult to observe at hadron colliders.

Contribution

It provides a detailed analysis of higgsino pair production at the ILC, demonstrating the collider's potential to discover or rule out natural SUSY through precision measurements.

Findings

Higgsinos are hard to detect at hadron colliders due to small mass splittings.

Electron-positron colliders can effectively search for light higgsinos.

Precision measurements at the ILC can reveal underlying SUSY parameters.

Abstract

A core prediction of natural Supersymmetry is the existence of four light higgsinos not too far above the mass of the $Z$ boson. The small mass splittings amongst the higgsinos -- typically 5-20\,GeV -- imply very little visible energy release from decays of heavier higgsinos. In particular, if other SUSY particles are quite heavy, as can be the case in SUSY with radiatively-driven naturalness, the higgsinos are extremely hard to detect at hadron colliders. The clean environment of electron-positron colliders with $\sqrt{s} > 2m_{\mathrm{higgsino}}$, however, would allow for a decisive search for the required light higgsinos. Thus, $e^+e^-$ colliders should either discover or exclude natural SUSY. We present a detailed study of higgsino pair production at the proposed International Linear $e^+e^-$ Collider which is under consideration for construction in Japan. A variety of precision measurements should allow for extraction of underlying parameters and provide a window onto physics at the grand unified scale.