The MSSM golden region and its collider signature

The “golden region” in the Minimal Supersymmetric Model (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 At is large, leading to a significant mass splitting between the two stop mass eigenstates. As a result, the decay t̃2 → t̃1Z 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 + E/T + 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. PACS. 14.80.Ly Supersymmetric partners of known particles – 12.60.Jv Supersymmetric models 1 The MSSM Golden Region In this talk (based on our recent paper [1]) we explore the idea that data and naturalness point to a particular ”golden” region within the Higgs and top sectors of the minimal supersymmetric model (MSSM), where the experimental bounds from non-observation of superpartners and the Higgs boson are satisfied and finetuning is close to the minimum value possible. We start by outlining the boundaries of the MSSM golden region. These are somewhat fuzzy due to an inherent lack of precision surrounding the concept of fine-tuning. Our goal is to understand the qualitative features by making approximations which greatly clarify the picture. The Higgs sector of the MSSM is strongly coupled to the top sector, but couplings to the rest of the MSSM are weaker. One may therefore begin by considering the Higgs and top sectors in isolation; that is, the gauge and non-top Yukawa couplings are set to zero. This is a good approximation as long as M1/Mt̃ <∼ 4, M2/Mt̃ <∼ 2, M3/Mt̃ <∼ 10,Mb̃ <∼ 35Mt̃/ tanβ, where g1,2,3 and M1,2,3 are the gauge couplings and (weak-scale) gaugino masses for U(1), SU(2) and SU(3), and Mt̃ and Mb̃ are the stop and sbottom mass scales. In this approximation, physics is described in terms of the holomorphic Higgs mass μ and the six parameters appearing in the soft Lagrangian for the Higgs and top sectors. Since the model has to reproduce the known EWSB scale, v = 174 GeV, only six parameters are independent. We choose the physical basis: tanβ, μ,mA, m̃1, m̃2, θt, (1) where mA is the CP-odd Higgs mass, m̃1 and m̃2 are stop eigenmasses (by convention, m̃2 > m̃1) and θt is the stop mixing angle. We will analyze the finetuning and Higgs mass constraints in this approximation and map out the golden region in the sixparameter space (1). Following Barbieri and Guidice [2], we quantify fine-tuning by computing