Phenomenology of the Minimal Supersymmetric Standard Model

Background: The recent discovery of a Standard Model (SM) – like Higgs boson underscores a theoretical problem that has been anticipated for decades, known as the hierarchy problem. Generically, particles that couple to the Higgs can give contributions to its mass that grow quadratically with energy, requiring a finely-tuned cancellation to produce the observed Higgs mass. Supersymmetry (SUSY) solves this problem by pairing each particle with a partner with the same charge and couplings but opposite spin-statistics, giving equal and opposite contributions to the Higgs mass. If SUSY solves the hierarchy problem, we expect to see new SUSY particles at around the TeV scale. This has motivated an ongoing experimental effort to discover SUSY particles, which has so far been unsuccessful. In this work, we consider the Minimal Supersymmetric SM (MSSM) and examine several current and near-future experiments to determine their sensitivity to different regions of the parameter space. Methods: Although it contains the minimal particle content for a supersymmetric theory, the MSSM is still described by over 100 free parameters. However, many of these parameters are strongly constrained by experimental results. This motivates us to consider a simplified case, the 19 parameter phenomenological MSSM (pMSSM), which captures most of the phenomenology of the general case. We survey the pMSSM by testing 3 × 10⁶ randomly-chosen points against experimental and theoretical constraints, and examine the properties of the 2.2 × 10⁵points that agree with all pre-LHC data. In particular, we consider their signatures in current and future LHC searches, direct and indirect dark matter searches, and precision measurements of the 125 GeV Higgs boson. Results: We find that current and planned experiments have an excellent sensitivity to a wide range of pMSSM models. Interestingly, LHC searches depend strongly on the masses of colored SUSY particles and of the lightest SUSY particle (LSP), which are less important for direct detection experiments and Higgs precision measurements. The LHC search sensitivity is therefore approximately independent from direct detection and Higgs measurement sensitivities. On the other hand, indirect dark matter searches with the planned Cherenkov Telescope Array benefit from large LSP masses, which are challenging for the LHC. In this case, therefore, we observe a strong complementarity between the two techniques. Finally, we find that “natural” models, which provide the best solution to the hierarchy problem (smallest amount of fine-tuning), are particularly good targets for LHC searches. Conclusion: The suite of proposed and planned experiments considered during the 2013 Snowmass process, including next-generation dark matter experiments, precision Higgs measurements at a linear collider, and a high luminosity run of the 14 TeV LHC, are sensitive to a wide variety of MSSM scenarios. Additionally, each experimental category plays an independent and important role in the search for SUSY.