Quest for precision in hadronic cross sections at low energy: Monte Carlo tools vs. experimental data

Institut für Physik Humboldt-Universität zu Berlin 12489 Berlin Germany; Dipartimento di Fisica dell’Università di Bologna 40126 Bologna Italy; INFN, Sezione di Bologna 40126 Bologna Italy; Novosibirsk State University 630090 Novosibirsk Russia; Università di Parma Dipartimento di Fisica 43100 Parma Italy; INFN, Gruppo Collegato di Parma 43100 Parma Italy; Università di Pavia Dipartimento di Fisica Nucleare e Teorica 27100 Pavia Italy; Bergische Universität Wuppertal Fachbereich C 42097 Wuppertal Germany
European Physical Journal C (Impact Factor: 5.25). 12/2009; DOI: 10.1140/epjc/s10052-010-1251-4
Source: arXiv

ABSTRACT We present the achievements of the last years of the experimental and theoretical groups working on hadronic cross section measurements at the low energy e+e- colliders in Beijing, Frascati, Ithaca, Novosibirsk, Stanford and Tsukuba and on tau decays. We sketch the prospects in these fields for the years to come. We emphasise the status and the precision of the Monte Carlo generators used to analyse the hadronic cross section measurements obtained as well with energy scans as with radiative return, to determine luminosities and tau decays. The radiative corrections fully or approximately implemented in the various codes and the contribution of the vacuum polarisation are discussed. Comment: Report of the "Working Group on Radiative Corrections and Monte Carlo Generators for Low Energies"; 99 pages, submitted to EPJC

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    ABSTRACT: We update our standard model predictions for g − 2 of the muon and for the hadronic contributions to the running of the QED coupling, Δα(5)had(M2Z). Particular emphasis is put on recent changes in the hadronic contributions from new data in the 2π channel and from the energy region just below 2 GeV. In particular, for the e+e− → π+π− contribution we include the recent 'radiative return' data from KLOE and BaBar. We also include the recent BaBar data on other exclusive channels. We make a detailed study of the effect of replacing the measurements of the inclusive cross section, σ(e+e− → hadrons), by the sum of the exclusive channels in the energy interval GeV, which includes a QCD sum-rule analysis of this energy region. Our favoured prediction for the muon anomalous magnetic moment is (g − 2)/2 = (11 659 182.8 ± 4.9) × 10−10 which is 3.3 σ below the present world-average measurement. We compare our g − 2 value with other recent calculations. Our prediction for the QED coupling, obtained via Δα(5)had(MZ2) = (276.26 ± 1.38) × 10−4 , is α(M2Z)−1 = 128.944 ± 0.019.
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