[Paper Review] The CMSSM Favoring New Territories: The Impact of New LHC Limits and a 125 GeV Higgs

Andrew Fowlie, M. Kazana+6 more|arXiv (Cornell University)|Jun 1, 2012

Particle physics theoretical and experimental studies47 citations

TL;DR

This paper updates the Constrained Minimal Supersymmetric Standard Model (CMSSM) using new LHC data, including 125 GeV Higgs constraints and improved limits on BR(Bs→μμ), while incorporating simulated detector efficiency for the CMS razor search. It identifies the A-funnel and stau-coannihilation regions as favored by the global fit, while the focus point region is now disfavored, leading to higher superpartner masses and lower spin-independent dark matter cross sections.

ABSTRACT

We present an updated and extended global analysis of the Constrained MSSM (CMSSM) taking into account new limits on supersymmetry from ~5/fb data sets at the LHC. In particular, in the case of the razor limit obtained by the CMS Collaboration we simulate detector efficiency for the experimental analysis and derive an approximate but accurate likelihood function. We discuss the impact on the global fit of a possible Higgs boson with mass near 125 GeV, as implied by recent data, and of a new improved limit on BR(B_s->\mu\mu). We identify high posterior probability regions of the CMSSM parameters as the stau-coannihilation and the A-funnel region, with the importance of the latter now being much larger due to the combined effect of the above three LHC results and of dark matter relic density. We also find that the focus point region is now disfavored. Ensuing implications for superpartner masses favor even larger values than before, and even lower ranges for dark matter spin-independent cross section, \sigma^{SI}_p s\gamma) and BR(B_s->\mu\mu).

Motivation & Objective

• To re-evaluate the CMSSM parameter space in light of new LHC data, including 5/fb of integrated luminosity.
• To incorporate updated experimental constraints from the CMS razor search by simulating detector efficiency and constructing an accurate likelihood function.
• To assess the impact of a 125 GeV Higgs boson and the improved BR(Bs→μμ) limit on the global fit of the CMSSM.
• To identify high-posterior-probability regions in CMSSM parameter space, particularly in relation to dark matter relic density and direct detection constraints.
• To update predictions for superpartner masses and spin-independent dark matter scattering cross sections.

Proposed method

• Simulate detector efficiency for the CMS razor search to derive an approximate but accurate likelihood function for the CMSSM parameter space.
• Integrate new LHC limits from ~5/fb of data, including the CMS razor analysis and updated BR(Bs→μμ) bounds.
• Apply Bayesian global fitting techniques to evaluate posterior probabilities across CMSSM parameters, incorporating dark matter relic density as a key constraint.
• Use the measured Higgs mass near 125 GeV as a fixed input in the likelihood evaluation to assess its impact on model compatibility.
• Perform a comparative analysis of CMSSM regions—stau-coannihilation, A-funnel, and focus point—based on posterior probability and consistency with data.
• Derive updated predictions for superpartner masses and the spin-independent dark matter scattering cross section (σ^SI_p).

Experimental results

Research questions

• RQ1 How do the latest LHC limits from ~5/fb of data affect the posterior probability of the CMSSM parameter space?
• RQ2 What is the impact of a 125 GeV Higgs boson on the global fit of the CMSSM, particularly in relation to the Higgs mass and electroweak symmetry breaking?
• RQ3 How does the improved BR(Bs→μμ) limit influence the viability of different CMSSM regions, especially the A-funnel and stau-coannihilation channels?
• RQ4 Which CMSSM regions—stau-coannihilation, A-funnel, or focus point—emerge as most favored under the combined constraints of LHC data, Higgs mass, and dark matter relic density?
• RQ5 What are the updated predictions for superpartner masses and the spin-independent dark matter scattering cross section in the preferred regions?

Key findings

• The A-funnel region has become significantly more favored in the CMSSM global fit due to the combined effect of the 125 GeV Higgs, improved BR(Bs→μμ) limit, and LHC 5/fb data.
• The stau-coannihilation region remains a high-posterior-probability region, maintaining strong compatibility with the data.
• The focus point region is now disfavored, indicating a reduced likelihood under the updated constraints.
• Superpartner masses are predicted to be even higher than previously estimated, particularly in the favored A-funnel and stau-coannihilation regions.
• The spin-independent dark matter scattering cross section (σ^SI_p) is now constrained to lower values, consistent with current direct detection limits.
• The BR(Bs→μμ) limit plays a key role in disfavoring certain CMSSM regions and reinforcing the preference for the A-funnel and stau-coannihilation channels.