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T: Fachverband Teilchenphysik

T 13: QCD (Theorie) 3

T 13.8: Talk

Thursday, March 1, 2012, 18:30–18:45, VG 3.103

Decay Rate of the Z-boson into hadrons at O(α_s⁴) — •Pavel Baikov², Konstantin Chetyrkin¹, Johann Kühn¹, and Jörg Rittinger¹ — ¹Institut für theoretische Teilchenphysik, KIT, Karlsruhe — ²Institute of Nuclear Physics, Moscow State University, Moscow

To calculate the decay rate of the Z-boson into hadrons (Γ_Z), one has to do two steps. First the heavy top quark has to be decoupled, which leads to an effective massless 5-flavour QCD. Second the imaginary part of the Z-propagator, which is related to Γ_Z due to the optical theorem, has to be calculated in this effective theory. This was done up to O(α_s⁴), including the calculation of 5-loop propagators.

Since Γ_Z is related to one of the most precise determinations of α_s, our calculation will improve the existing 3 loop fit, resulting in a small shift in α_s and a reduction of the theory uncertainty.