[Paper Review] Improving SUSY Spectrum Determinations at the LHC with Wedgebox and Hidden Threshold Techniques

Mike Bisset, N. Kersting+1 more|arXiv (Cornell University)|Jun 16, 2008

Particle physics theoretical and experimental studies3 references15 citations

TL;DR

This paper proposes a novel fusion of the wedgebox and mass-shell techniques to improve sparticle mass spectrum determinations at the LHC. By using the wedgebox method to isolate purer event samples before applying mass-shell equations, the approach reduces errors from incorrect decay chain assumptions and enhances reconstruction accuracy, offering a robust, data-driven method for precise SUSY spectrum measurements.

ABSTRACT

The LHC has the potential not only to discover supersymmetry (SUSY), but also to permit fairly precise measurements of at least a portion of the sparticle spectrum. Proposed mass reconstruction methods rely upon either inverting invariant mass endpoint expressions or upon solving systems of mass-shell equations. These methodologies suffer from the weakness that one certain specific sparticle decay chain is assumed to account for all the events in the sample. Taking two examples of techniques utilizing mass-shell equations, it is found that also applying the wedgebox technique allows for the isolation of a purer event sample, thus avoiding errors, possibly catastrophic, due to mistaken assumptions about the decay chains involved and simultaneously improving accuracy. What is innovative is using endpoint measurements (via the wedgebox technique) to obtain a more homogeneous, well-understood sample set rather than just using said endpoints to constrain the values of the masses (here found by the mass-shell technique). The fusion of different established techniques in this manner represents a highly profitable option for LHC experimentalists who will soon have data to analyze.

Motivation & Objective

• To address inaccuracies in SUSY sparticle mass spectrum determinations at the LHC caused by incorrect assumptions about decay chains.
• To reduce systematic errors arising when invariant mass endpoint or mass-shell methods assume a single decay chain for all events.
• To improve the purity and homogeneity of event samples used in mass reconstruction, thereby increasing measurement accuracy.
• To demonstrate that endpoint measurements via the wedgebox technique can serve as a preselection tool rather than just a constraint method.
• To provide experimentalists with a more reliable, integrated methodology for analyzing upcoming LHC data.

Proposed method

• The wedgebox technique is applied to isolate a cleaner, more homogeneous sample of events by selecting regions in kinematic space where specific decay chains dominate.
• Mass-shell equations are then solved on the purified event sample to determine sparticle masses with reduced contamination from other decay modes.
• The method inverts the traditional use of endpoints—instead of relying on endpoints to constrain masses, they are used to define the wedgebox region for sample selection.
• The approach combines established techniques in a synergistic way, leveraging the wedgebox’s ability to suppress background and misidentified decay chains.
• The technique is validated on two example decay chains, showing improved consistency and reduced sensitivity to model assumptions.
• The fusion of methods allows for more robust mass determinations even when multiple decay channels are present in the data.

Experimental results

Research questions

• RQ1 Can the wedgebox technique be used to improve the purity of event samples used in sparticle mass reconstruction at the LHC?
• RQ2 How does combining the wedgebox method with mass-shell equations reduce errors from incorrect decay chain assumptions?
• RQ3 To what extent does pre-selection via wedgebox endpoints enhance the accuracy of mass spectrum determinations compared to standard endpoint or mass-shell methods?
• RQ4 Can the wedgebox technique serve a dual role—both as a sample purification tool and as a source of kinematic constraints—without compromising precision?
• RQ5 How does the fused approach perform under realistic LHC conditions with overlapping decay chains?

Key findings

• The fusion of wedgebox and mass-shell techniques results in a significantly purer event sample, reducing contamination from misidentified or competing decay chains.
• By isolating events using wedgebox-defined regions, the method minimizes catastrophic errors that arise when a single decay chain is incorrectly assumed for all events.
• The approach improves the accuracy of sparticle mass measurements by reducing systematic uncertainties linked to model-dependent assumptions.
• The study demonstrates that endpoint measurements via the wedgebox technique are most effective when used as a preselection mechanism rather than solely as a constraint on mass values.
• The method provides a robust, data-driven framework for LHC experimentalists to analyze SUSY spectra with greater confidence, especially in complex event samples.
• The technique is shown to be effective across multiple decay chain examples, indicating broad applicability to future LHC data analysis.