[Paper Review] Susy searches in combined LHC/LC analyses

Gudrid Moortgat‐Pick, K. Desch+3 more|ArXiv.org|Oct 7, 2004

Particle physics theoretical and experimental studies3 citations

TL;DR

This paper proposes a synergistic analysis framework combining data from the Large Hadron Collider (LHC) and a future Linear Collider (LC) to improve supersymmetry (SUSY) parameter determination and heavy particle identification. By using precise LC measurements of light SUSY particles to constrain LHC analyses, the method enhances sensitivity to marginal signals and enables accurate mass reconstruction of heavy neutralinos, with feedback from LHC results further refining LC parameter determinations.

ABSTRACT

We present a case study for the synergy of combined LHC and LC analyses in Susy searches in which simultaneous running of both machines is very important. In this study only light non-coloured Susy particles are accessible at a Linear Collider with an initial energy of $\sqrt{s}=500$ GeV. Nevertheless the precise analysis at the LC leads to an accurate Susy parameter determination and prediction of heavy Susy particles. Providing these LC results as input for the LHC analyses could be crucial for the identification of signals resulting in a direct measurement of the heavy neutralinos. The interplay of the LHC and LC will thus provide an important consistency test of the underlying model.

Motivation & Objective

• Address the challenge of determining the large number of free parameters in the unconstrained MSSM.
• Overcome the ambiguity in identifying heavy SUSY particles from overlapping decay signatures at the LHC.
• Leverage the Linear Collider’s precision measurements to reduce uncertainties in SUSY parameter space.
• Establish a feedback loop between LHC and LC to iteratively improve model consistency and parameter accuracy.
• Enable a robust, model-independent test of the underlying SUSY framework through combined experimental input.

Proposed method

• Use precise LC measurements at √s = 500 GeV to determine masses and cross-sections of light non-coloured SUSY particles (e.g., charginos, neutralinos, sleptons).
• Apply polarized e+e− collisions at the LC to enhance sensitivity to quantum numbers, mixing angles, and couplings.
• Feed LC-derived SUSY parameters and predicted masses of heavy particles (e.g., m~χ⁰₄ ≈ 378.2 ± 8.1 GeV) into LHC event simulations.
• Utilize kinematic edge techniques at the LHC to identify decay chains involving heavy neutralinos, with LC predictions reducing ambiguity.
• Perform joint fits of multiple kinematic edges to constrain the lightest SUSY particle (LSP) mass and improve signal identification.
• Implement iterative feedback: use refined LHC results to further constrain LC parameter determinations, enhancing overall precision.

Experimental results

Research questions

• RQ1 How can the Linear Collider’s precision measurements improve the identification of heavy SUSY particles in complex LHC decay chains?
• RQ2 To what extent does incorporating LC-predicted masses reduce the uncertainty in LHC-based mass reconstruction of heavy neutralinos?
• RQ3 Can the combined LHC+LC analysis provide a consistent, model-independent determination of MSSM parameters like M₁, M₂, μ, and tanβ?
• RQ4 How does the feedback loop between LHC and LC data improve the accuracy of SUSY parameter extraction beyond individual collider capabilities?
• RQ5 What is the impact of LC data on resolving ambiguities in LHC edge interpretations, particularly for overlapping final states?

Key findings

• The LC 500 phase enables a precise determination of light SUSY particle masses and couplings, with 1σ errors of δ(M₁) = 0.2 GeV, δ(M₂) = 0.6 GeV, δ(μ) = 8.9 GeV, and δ(tanβ) = 1.5.
• LC data predict the mass of the heavy neutralino ~χ⁰₄ as 378.2 ± 8.1 GeV, which is crucial for identifying its decay chain at the LHC.
• When LC predictions are used in LHC analyses, the dilepton edge from ~χ⁰₄ decay is clearly identified at mₗₗ ≈ 377.87 ± 2.23 GeV, significantly improving signal clarity.
• The LHC’s measurement of m~χ⁰₂ improves to δ(m~χ⁰₂) = 0.08 GeV due to the precise knowledge of the LSP mass m~χ⁰₁ from LC input.
• The combined LHC+LC 500 analysis reduces uncertainties in fundamental SUSY parameters: δ(M₁) = 0.1 GeV, δ(M₂) = 0.3 GeV, δ(μ) = 2.1 GeV, and δ(tanβ) = 0.6 GeV.
• The iterative feedback loop between LHC and LC leads to a self-consistent, high-precision determination of MSSM parameters, validating the underlying SUSY model.