[Paper Review] The Status of Supersymmetry after the LHC Run 1

P. Bechtle, Tilman Plehn+1 more|arXiv (Cornell University)|Jun 9, 2015

Particle physics theoretical and experimental studies112 references4 citations

TL;DR

This paper reviews the status of supersymmetry (SUSY) following LHC Run 1, evaluating its theoretical motivations, experimental searches across multiple final states, and global fits to constraints. Despite no direct discovery, the LHC data strongly constrain SUSY models—particularly the CMSSM—excluding them at 95% CL, while future Run 2 data is expected to provide definitive answers on the existence of strongly interacting SUSY states at the TeV scale.

ABSTRACT

Supersymmetry (SUSY) is a complete and renormalisable candidate for an extension of the Standard Model. At an energy scale not too far above the electroweak scale it would solve the hierarchy problem of the SM Higgs boson, dynamically explain electroweak symmetry breaking, and provide a dark-matter candidate. Since it doubles the Standard Model degrees of freedom, SUSY predicts a large number of additional particles, whose properties and effects on precision measurements can be explicitly predicted in a given SUSY model. In this review the motivation for SUSY is outlined, the various searches strategies for SUSY particles at the LHC are described, and the status of SUSY in global analyses after the LHC Run 1 is summarized.

Motivation & Objective

• To assess the viability of supersymmetry as a solution to the hierarchy problem and unification of gauge couplings.
• To evaluate the impact of LHC Run 1 data on SUSY models, particularly in light of the observed Higgs boson mass and dark matter constraints.
• To summarize direct and indirect experimental limits on SUSY particles from Run 1, including searches in jets + missing transverse momentum, leptonic final states, and exotic signatures.
• To examine the role of simplified models and global fits in constraining SUSY parameter spaces.
• To project the discovery potential of LHC Run 2 for SUSY, especially for gluinos and third-generation squarks.

Proposed method

• Utilizes global fits combining direct LHC searches, low-energy precision measurements, cosmological data, and B-factory results to constrain SUSY models.
• Employs simplified model frameworks to interpret exclusion and discovery reach in key SUSY channels, such as gluino and top squark decays.
• Analyzes experimental results from ATLAS and CMS in final states with jets, leptons, photons, and missing transverse energy ($E^\text{miss}_\mathrm{T}$).
• Applies 95% confidence level (CL) exclusion limits from Run 1 data to benchmark models like the CMSSM and mSUGRA.
• Projects discovery reach for LHC Run 2 using luminosity scenarios of 300 fb$^{-1}$ and 3000 fb$^{-1}$ in mass planes such as $\tilde{g}$–$\tilde{\chi}^0_1$, $\tilde{t}_1$–$\tilde{\chi}^0_1$, and $\tilde{\chi}^\pm_1$–$\tilde{\chi}^0_1$.
• Considers kinematic challenges such as compressed spectra and R-parity-violating scenarios that reduce trigger and selection efficiency.

Experimental results

Research questions

• RQ1 To what extent do LHC Run 1 results exclude the CMSSM and other constrained SUSY models?
• RQ2 How do direct searches for SUSY particles in final states with jets, leptons, photons, and missing energy constrain the parameter space of the MSSM?
• RQ3 What is the discovery potential for SUSY in LHC Run 2, particularly for gluinos and top squarks, under high-luminosity scenarios?
• RQ4 How do indirect constraints—such as the anomalous magnetic moment of the muon $(g-2)_\mu$—interact with direct LHC limits to shape the viable SUSY parameter space?
• RQ5 In what cases do kinematic effects (e.g., compressed spectra) significantly reduce the sensitivity of SUSY searches, and how does this affect model exclusion?

Key findings

• The CMSSM is excluded at 95% confidence level by the combination of Higgs mass measurements, direct LHC SUSY searches, and low-energy precision data.
• No statistically significant signal for new physics was observed in LHC Run 1, despite extensive searches across multiple final states.
• The observed Higgs boson mass of approximately 125 GeV is consistent with MSSM expectations and does not rule out the model.
• The discovery reach for gluino pair production in the $\tilde{g} \to q\bar{q}\tilde{\chi}^0_1$ channel extends to masses above 2 TeV at 3000 fb$^{-1}$ luminosity.
• Compressed spectra—where the mass splitting between the lightest supersymmetric particle and its parent particle is small—significantly reduce trigger and selection efficiency, weakening exclusion and discovery potential.
• Prospects for LHC Run 2 are strong, with the potential to definitively test the MSSM and models with strongly interacting SUSY states at the few-TeV scale.