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[2601.02484] Resummation of the C-Parameter Sudakov Shoulder Using Effective Field Theory

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Abstract:The C-parameter distribution in $e^+e^-$ annihilation exhibits a kinematic shoulder at $C = 3/4$, where three-parton final states reach their maximum and a fourth parton is required to exceed it. This boundary generates large logarithms that must be resummed. Using soft-collinear effective theory, we derive a factorization theorem involving new jet and soft functions specific to the C-parameter measurement, in which soft radiation contributes quadratically in transverse momentum. This quadratic structure explains the step discontinuity at leading order. We compute all ingredients at one loop, validate against Monte Carlo, and present matched NLL+NLO results. Unlike thrust and heavy jet mass, the C-parameter has no Sudakov--Landau pole, making momentum-space resummation straightforward. All calculations, numerical analysis, and manuscript preparation were performed by Claude, an AI assistant developed by Anthropic, working under physicist supervision.

[2601.02484] Resummation of the C-Parameter Sudakov Shoulder Using Effective Field Theory Skip to main content arXiv is now an independent nonprofit! Learn more × Search arXiv Press Enter to search · Advanced search --> High Energy Physics - Phenomenology arXiv:2601.02484 (hep-ph) [Submitted on 5 Jan 2026] Title: Resummation of the C-Parameter Sudakov Shoulder Using Effective Field Theory Authors: Matthew D. Schwartz View a PDF of the paper titled Resummation of the C-Parameter Sudakov Shoulder Using Effective Field Theory, by Matthew D. Schwartz View PDF HTML (experimental) Abstr

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