Using an Effective Charges Method to extract Lambda-MS-bar from event shape moments in e+e- annihilation

Details Using an Effective Charges Method to extract Lambda-MS-bar from event shape moments in e+e- annihilation Using an Effective Charges Method to extract Lambda-MS-bar from event shape moments in e+e- annihilation

2011-08-31

arxiv.org/abs/1108.6204v2

Physics

High Energy Physics

High Energy Physics - Phenomenology

43 pages, 16 figures, Extended Conclusions section, minor textual editing, slight changes to some tabulated values, overall co

Scientific paper

We use an Effective Charges (ECH) method to extract Lambda-MS-bar, and hence alpha_s(M_z), from event shape moments in e+e- annihilation. We compare these results with ones obtained using standard MS-bar perturbation theory. The ECH method at NLO is found to perform better than standard MS-bar perturbation theory when applied to means of event shape observables. For example, when we apply the NLO ECH method to <1-T> we get alpha_s(M_z)=0.1193\pm0.0003. However ECH at NNLO is found to work less well than ECH at NLO, and the ECH method also fails to describe data for higher moments of event shapes. We attempt to explain this by considering the ECH beta-function as an asymptotic series. We also examine the effect of adding two different models for non-perturbative power corrections to the perturbative approximation given by the ECH method and MS-bar perturbation theory. Whilst only small power corrections are required when using ECH at NLO, it is found that these models are insufficient to couteract the undesirable behaviour of ECH at NNLO.

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