A Collider Signature of the Supersymmetric Golden Region

TL;DR

The paper tackles the tension between naturalness and experimental bounds in the MSSM by proposing a 'golden region' where fine-tuning is minimized yet LEP/Higgs constraints are satisfied. It develops a six-parameter framework $(\tan\beta,\mu,m_A,\tilde{m}_1,\tilde{m}_2,\theta_t)$ and uses Barbieri–Giudice tuning measures $A(\cdot)$ together with an analytic Higgs-mass formula to carve out the viable region, further constrained by $\Delta\rho$, $b\to s\gamma$, and $g-2$. The golden region predicts light stops with substantial mass splitting and nonzero mixing, making the decay $\tilde{t}_2 \to \tilde{t}_1 Z$ a characteristic collider feature and motivating an LHC search in the inclusive channel $Z+2j_b+\mathrm{MET}+X$. The authors present a benchmark point and a detailed collider study showing that this signature can be observable at the LHC, while also discussing alternative interpretations and strategies to distinguish them, thereby providing a direct test of naturalness-inspired MSSM scenarios and a handle on the stop spectrum.

Abstract

Null results of experimental searches for the Higgs boson and the superpartners imply a certain amount of fine-tuning in the electroweak sector of the Minimal Supersymmetric Standard Model (MSSM). The "golden region" in the MSSM parameter space is the region where the experimental constraints are satisfied and the amount of fine-tuning is minimized. In this region, the stop trilinear soft term is large, leading to a significant mass splitting between the two stop mass eigenstates. As a result, the decay of the heavier stop into the lighter stop and a Z boson is kinematically allowed throughout the golden region. We propose that the experiments at the Large Hadron Collider (LHC) can search for this decay through an inclusive signature, Z+2jb+missing Et+X. We evaluate the Standard Model backgrounds for this channel, and identify a set of cuts that would allow detection of the supersymmetric contribution at the LHC for the MSSM parameters typical of the golden region. We also discuss other possible interpretations of a signal for new physics in the Z+2jb+missing Et+X channel, and suggest further measurements that could be used to distinguish among these interpretations.