[Paper Review] Report of the Beyond the MSSM Subgroup for the Tevatron Run II SUSY/Higgs Workshop

S. Ambrosanio, Howard Baer+31 more|ArXiv.org|Jun 15, 2000

Particle physics theoretical and experimental studies5 citations

TL;DR

This paper explores non-minimal supersymmetry models beyond the MSSM, focusing on extended gauge symmetries, R-parity violation, and gravity-mediated SUSY breaking with non-standard soft-breaking parameters. It demonstrates that these models yield vastly different Tevatron discovery prospects, with gauge kinetic mixing in E6-inspired Z′ models significantly altering search reach and complicating model discrimination, even when multiple observables are used.

ABSTRACT

There are many low-energy models of supersymmetry breaking parameters which are motivated by theoretical and experimental considerations. Here, we discuss some of the lesser-known theories of low-energy supersymmetry, and outline their phenomenological consequences. In some cases, these theories have more gauge symmetry or particle content than the Minimal Supersymmetric Standard Model. In other cases, the parameters of the Lagrangian are unusual compared to commonly accepted norms (e.g., Wino LSP, heavy gluino LSP, light gluino, etc.). The phenomenology of supersymmetry varies greatly between the different models. Correspondingly, particular aspects of the detectors assume greater or lesser importance. Detection of supersymmetry and the determination of all parameters may well depend upon having the widest possible view of supersymmetry phenomenology.

Motivation & Objective

• To explore low-energy supersymmetry models that extend beyond the Minimal Supersymmetric Standard Model (MSSM), including those with additional gauge symmetries or non-standard soft-breaking parameters.
• To assess the discovery potential for supersymmetry at the upgraded Tevatron under a wide range of beyond-MSSM scenarios.
• To evaluate the impact of gauge kinetic mixing (GKM) on Z′ boson couplings and search reach in E6-inspired models.
• To examine the challenges in distinguishing between models with similar signatures, such as Left-Right symmetric models and E6-based Z′ models.
• To highlight the importance of using multiple observables (e.g., Pτ, Rbl, Afb) for model discrimination in the presence of GKM-induced parameter degeneracy.

Proposed method

• Analyzes a broad class of supersymmetry models with extended matter and gauge content, including those with R-parity violation and non-universal soft-breaking parameters.
• Applies renormalization group equations (RGEs) to compute gauge kinetic mixing (GKM) parameters δ and λ in E6-inspired models with incomplete GUT representations below the GUT scale.
• Uses Monte Carlo scans over θ, δ, and λ parameters to determine the allowed parameter space for E6 Z′ couplings and their phenomenological consequences.
• Evaluates the Tevatron discovery reach for Z′ bosons using Drell-Yan production, incorporating GKM effects and assuming luminosities of 2 and 30 fb⁻¹.
• Compares model predictions across different benchmark models (e.g., A, B, L, U, SM couplings, W3) using observables like Pτ, Rbl, and Afb to assess distinguishability.
• Considers the implications of a light gravitino LSP and non-standard LSPs (e.g., wino, heavy or light gluino) in phenomenological analyses.

Experimental results

Research questions

• RQ1 How do gauge kinetic mixing effects alter the couplings and detectability of Z′ bosons in E6-inspired models at the Tevatron?
• RQ2 To what extent do non-minimal soft-SUSY-breaking parameters and extended gauge sectors change the discovery potential for supersymmetry at the Tevatron?
• RQ3 Can models with similar signatures—such as Left-Right symmetric models and E6-based Z′ models—be distinguished using multiple precision measurements?
• RQ4 What is the effective search reach for Z′ bosons in the presence of GKM, particularly in the case of leptophobic Z′ bosons?
• RQ5 How does the inclusion of multiple observables (Pτ, Rbl, Afb) improve model discrimination in the context of GKM-induced parameter degeneracy?

Key findings

• Gauge kinetic mixing (GKM) in E6-inspired models modifies Z′ couplings, leading to a non-trivial parameter space with δ ranging from -0.286 to 0.250 at one-loop level.
• The worst-case search reach for a Z′ boson in an η-type E6 model with λ=0.862 and δ=-0.286 is 482 GeV at 2 fb⁻¹ and 736 GeV at 30 fb⁻¹, significantly reduced from naive expectations.
• The 'leptophobic hole' in the search reach—where Z′ does not couple to leptons—disappears due to GKM, but a dimple in the reach occurs when coupling to u-quarks vanishes.
• With GKM, the E6 model's parameter space spreads into broad regions in θ–δ–λ space, causing significant overlap with Left-Right symmetric models and SM-coupled Z′ models.
• Even with all three observables (Pτ, Rbl, Afb), model separation between E6 and Left-Right models remains difficult, and SM-coupled Z′ models become indistinguishable from E6 models.
• The analysis underscores that multiple precision measurements are essential for model discrimination, as single-channel searches (e.g., Drell-Yan) can fail in the presence of GKM.