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Order alphas4 QCD corrections to Z and tau decays
P A Baikov1, K G Chetyrkin, J H Kühn
1Institute of Nuclear Physics, Moscow State University, Moscow 119899, Russia.
Physical Review Letters
|September 4, 2008
Summary
New calculations in perturbative quantum chromodynamics (QCD) stabilize the strong coupling constant (αs) series. This precision test of asymptotic freedom yields a highly accurate value for αs.
Area of Science:
- High-energy particle physics
- Quantum Chromodynamics (QCD)
- Perturbative calculations
Background:
- Electron-positron annihilation and Z boson/tau lepton decays provide crucial data for determining the strong coupling constant.
- Previous calculations were limited in precision due to theoretical uncertainties.
Purpose of the Study:
- To evaluate higher-order corrections (order αs⁴) for key processes in perturbative QCD.
- To improve the precision and stability of the strong coupling constant determination.
- To test the principle of asymptotic freedom by comparing αs values at different energy scales.
Main Methods:
- Application of recently developed methods for evaluating five-loop amplitudes in perturbative QCD.
- Calculation of nonsinglet cross-section corrections for electron-positron annihilation.
- Evaluation of decay rates for Z boson and tau lepton into hadrons.
Main Results:
- Significant stabilization of the perturbative series for the evaluated quantities.
- Reduction in theoretical uncertainty for the strong coupling constant (αs).
- A combined value of αs(MZ) = 0.1198 ± 0.0015 obtained from Z and tau decays, representing an order αs⁴ result.
Conclusions:
- The new calculations provide a more precise and stable determination of the strong coupling constant.
- The agreement of αs values at different energies strongly supports asymptotic freedom.
- This result represents one of the most precise determinations of αs to date at order αs⁴.
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