Göttingen 2025 – scientific programme
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T: Fachverband Teilchenphysik
T 31: Flavour physics II
T 31.3: Talk
Tuesday, April 1, 2025, 16:45–17:00, VG 1.104
Bc → ηc form factors at large recoil: Interplay of soft-quark and soft-gluon double logarithms — Guido Bell1, Philipp Böer2, Thorsten Feldmann1, •Dennis Horstmann1, and Vladyslav Shtabovenko1 — 1Theoretische Physik 1, Center for Particle Physics Siegen, Universität Siegen — 2CERN, Theoretical Physics Department
Soft-Collinear Effective Theory is an important tool used for setting up factorisation theorems and achieving resummations to all orders in perturbation theory. While most conceptual problems appearing in calculations at leading power have been understood, at subleading power endpoint divergent convolution integrals appear in the factorisation theorems preventing the use of renormalization group equations for resummations. While this problem has been solved in a few collider processes, it persists in exclusive B-decays. We therefore resort to diagrammatic resummation techniques to derive the double-logarithmic series of the soft-overlap contribution to Bc → ηc transition form factors, assuming the scale hierarchy mb ≫ mc≫ ΛQCD. We find that the leading double logarithms arise from a peculiar interplay of soft-quark endpoint logarithms from ladder diagrams with energy-ordered spectator-quark propagators, as well as standard Sudakov-type soft-gluon corrections. We elucidate the all-order systematics, and show that their resummation proceeds via a novel type of integral equations.
Keywords: Soft-Collinear Effective Theory; Resummation; Factorisation; Subleading power; Endpoint divergence