[Paper Review] Has SUSY Gone Undetected in 9-jet Events? A Ten-Fold Enhancement in the LHC Signal Efficiency

Tianjun Li, James A. Maxin+2 more|arXiv (Cornell University)|Aug 25, 2011

Particle physics theoretical and experimental studies61 references20 citations

TL;DR

This paper proposes that supersymmetry (SUSY) in the No-Scale $Φ$-$SU(5)$ model may have evaded detection at the LHC due to suboptimal search strategies, demonstrating that a tailored set of selection cuts targeting ultra-high jet multiplicity (e.g., 9-jet events) can enhance signal visibility by a factor of ten. The study establishes first exclusion bounds for this model class, showing viable parameter space with LSP mass ≥92 GeV and gluino mass ≥658 GeV, while explaining observed CMS excesses.

ABSTRACT

On the heels of the first analysis of LHC data eclipsing the inverse femtobarn integrated luminosity milestone, we undertake a detailed comparison of the most recent experimental results with Monte Carlo simulation of the full "bare-minimally constrained" parameter space of the class of supersymmetric models which go by the name of No-Scale FSU5. We establish the first sparticle exclusion boundaries on these models, finding that the LSP mass should be at least about 92 GeV, with a corresponding boundary gaugino mass M_1/2 above about 485 GeV. In contrast to the higher mass constraints established for the CMSSM, we find the minimum exclusion boundary on the FSU5 gluino and heavy squark masses resides in the range of 658-674 GeV and 854-1088 GeV, respectively, with a minimum light stop squark mass of about 520 GeV. Moreover, we show that elements of the surviving parameter space not only escape the onslaught of LHC data which is currently decimating the standard mSUGRA/CMSSM benchmarks, but are further able to efficiently explain certain tantalizing production excesses over the SM background which have been reported by the CMS collaboration. We also extend this study comparatively to five distinct collider energies and four specific cut methodologies, including a proposed set of selection cuts designed to reveal the natural ultra-high jet multiplicity signal associated with the stable mass hierarchy m_t < m_g < m_q of the FSU5 models. By so doing, we demonstrate that a rather stable enhancement in model visibility, conservatively of order ten, may be attained by adoption of these cuts, which is sufficient for an immediate and definitive testing of a majority of the model space using only the existing LHC data set. We stress the point that habits established in lower jet multiplicity searches do not necessarily carry over into the ultra-high jet multiplicity search regime.

Motivation & Objective

• To re-evaluate the viability of the No-Scale $Φ$-$SU(5)$ supersymmetric model in light of the first 1.1 fb⁻¹ of LHC data.
• To address the failure of standard mSUGRA/CMSSM-based search strategies to detect this model, despite its naturalness and low fine-tuning.
• To identify and validate a new set of selection cuts that maximize signal visibility for this model class in ultra-high jet multiplicity events.
• To demonstrate that existing LHC data can definitively test a majority of the No-Scale $Φ$-$SU(5)$ parameter space using these optimized cuts.

Proposed method

• Performed a detailed comparison between experimental LHC data (1.1 fb⁻¹) and Monte Carlo simulations of the full bare-minimally constrained parameter space of the No-Scale $Φ$-$SU(5)$ model.
• Applied the same CMS data selection methodology used in the 2011 analysis to ensure consistency and direct comparability.
• Designed and tested a new set of kinematic selection cuts optimized for the stable mass hierarchy $m_{\tilde{t}} < m_{\tilde{g}} < m_{\tilde{q}}$, which favors high jet multiplicity (e.g., 9-jet) final states.
• Evaluated the signal enhancement factor across four different collider energies and four cut strategies, including the proposed high-multiplicity cuts.
• Used the observed CMS production excesses over SM background as a benchmark to test model compatibility.
• Calibrated the analysis using limited background simulations supplemented with actual LHC observations to ensure realism.

Experimental results

Research questions

• RQ1 Can the No-Scale $Φ$-$SU(5)$ model evade current LHC exclusion limits despite being a viable natural SUSY framework?
• RQ2 To what extent can signal visibility be enhanced in high jet multiplicity final states through optimized selection cuts?
• RQ3 Do the observed CMS excesses in 9-jet events correlate with viable parameter space in the No-Scale $Φ$-$SU(5)$ model?
• RQ4 How do the exclusion bounds for the No-Scale $Φ$-$SU(5)$ model compare to those of the CMSSM and mSUGRA?
• RQ5 Is the standard mSUGRA/CMSSM-based search strategy fundamentally inadequate for detecting certain viable SUSY models?

Key findings

• The first exclusion boundaries for the No-Scale $Φ$-$SU(5)$ model have been established, with the LSP mass constrained to be at least 92 GeV and the gaugino mass $M_{1/2}$ above 485 GeV.
• The minimum gluino mass in the viable parameter space ranges from 658 to 674 GeV, and the minimum heavy squark mass from 854 to 1088 GeV.
• The light stop squark mass has a minimum boundary of approximately 520 GeV in the surviving parameter space.
• A ten-fold enhancement in signal visibility is achievable by adopting the proposed high-multiplicity jet cuts, which is stable across different LHC energies and model points.
• The viable parameter space of the No-Scale $Φ$-$SU(5)$ model not only evades current LHC exclusions but also efficiently explains the CMS-reported production excesses over SM background.
• The study demonstrates that standard search strategies based on lower jet multiplicity are insufficient for detecting this model, and that habits from such searches do not transfer to ultra-high jet multiplicity regimes.