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Comment: 6 pages and 1 figure. To appear in the proceedings of the XXXIVth Rencontres de Moriond on "Gravitational Waves and Experimental Gravity" (les Arcs, Jan.99)
Comment: 45 pages, 15 figures; v2: e+e--based evaluation unchanged; modifications of the tau-based estimate: added OPAL data, corrected evaluation of Sew factor, used re-evaluated error matrices in preliminary ALEPH spectral functions; v3: updated arXiv abstract, no changes in results
Vacuum polarization integrals involve the vector spectral functions which can be experimentally determined from two sources: (i) e+e- annihilation cross sections and (ii) hadronic tau decays. Recently results with comparable precision have become available from CMD-2 on one side, and ALEPH and CLEO on the other. The comparison of the respective spectral functions involves a correction from isospin-breaking effects which is evaluated. After correction it is found that the dominant 2pi spectral functions do not agree within experimental and theoretical uncertainties. Some problems are also found for the 4pi spectral functions where different experiments do not agree well with each other. The consequences of these discrepancies for vacuum polarization calculations are presented, with emphasis on the muon anomalous magnetic moment. The wor...
An update of the ALEPH non-strange spectral functions from hadronic $\tau$ decays is presented. Compared to the 2005 ALEPH publication, the main improvement results from the use of a new method to unfold the measured mass spectra from detector effects. This procedure also corrects a previous problem in the correlations between the unfolded mass bins. Results from QCD studies and for the evaluation of the hadronic vacuum polarisation contribution to the anomalous muon magnetic moment are derived using the new spectral functions. They are found in agreement with published results based on the previous set of spectral functions.
We revisit the determination of alpha_s(m_tau) using a fit to inclusive tau hadronic spectral moments in light of (1) the recent calculation of the fourth-order perturbative coefficient K_4 in the expansion of the Adler function, (2) new precision measurements from BABAR of e+e- annihilation cross sections, which decrease the uncertainty in the separation of vector and axial-vector spectral functions, and (3) improved results from BABAR and Belle on tau branching fractions involving kaons. We estimate that the fourth-order perturbative prediction reduces the theoretical uncertainty, introduced by the truncation of the series, by 20% with respect to earlier determinations. We discuss to some detail the perturbative prediction and show that the effect of the incomplete knowledge of the series is reduced by using the so-called contour-imp...
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