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T: Teilchenphysik

T 408: QCD II

T 408.5: Vortrag

Mittwoch, 12. März 2003, 15:00–15:15, SFO11

On the Behavior of the Effective QCD Coupling α_τ(s) at Low Scales — •Sven Menke^1,2, Stanley J. Brodsky¹, Carlos Merino^1,3, and Johan Rathsman⁴ — ¹Stanford Linear Accelerator Center, Stanford University, Stanford, California 94309 — ²now at Max-Planck-Institut für Physik, Föhringer Ring 6, 80805 München, Germany — ³now at Department of Particle Physics, University of Santiago de Compostela, 15706 Santiago de Compostela, Spain — ⁴High Energy Physics, Uppsala University, Box 535, S-751 21 Uppsala, Sweden

The hadronic decays of the τ lepton can be used to determine the effective charge ατ(mτ′2) for a hypothetical τ-lepton with mass in the range 0<mτ′<mτ. This definition provides a fundamental definition of the QCD coupling at low mass scales. We study the behavior of ατ at low mass scales directly from first principles and without any renormalization-scheme dependence by looking at the experimental data from the OPAL Collaboration. The results are consistent with the freezing of the physical coupling at mass scales s = mτ′2 of order 1 GeV2 with a magnitude ατ∼ 0.9 ± 0.1.