Improved alpha_s from Tau Decays

We present an update of the measurement of alpha_s(m_tau) from ALEPH tau hadronic spectral functions. We report a study of the perturbative prediction(s) showing that the fixed-order perturbation theory manifests convergence problems not presented in the contour-improved calculation. Potential systematic effects from quark-hadron duality violations are estimated to be within the quoted systematic errors. The fit result is alpha_s(m_tau) = 0.344 +- 0.005 +- 0.007, where the first error is experimental and the second theoretical. After evolution, the alpha_s(M_Z) determined from tau data is the most precise one to date, in agreement with the corresponding NNNLO value derived from Z decays.Comment: 4pages, 1 figure, Contribution to the proceedings of Moriond 2008, QCD sessio

Measurement of hadronic cross sections at BABAR with ISR and implications for the muon (g-2)

The ISR method has been largely exploited by the BABAR experiment, for measuring numerous channels of the cross section e+e- into hadrons. For the pi+pi-(gamma) and K+K-(gamma) channels, BABAR has pioneered the method based on the ratio between the hadronic mass spectra and the mu+mu-(gamma) one. This method allows to cancel many systematic uncertainties in the ratio, hence the precise measured cross sections. Many multihadronic channels have also been studied using the ISR method, and cross sections have been published. These experimental results have also been exploited for phenomenological studies, like the determination of the hadronic contribution to the anomalous magnetic moment of the muon (g-2)_mu.Comment: 10 pages, 3 figures. Contribution to the proceedings of the PHOTON2013 conference. Talk presented on behalf of the BABAR collaboratio

An iterative, dynamically stabilized method of data unfolding

We propose a new iterative unfolding method for experimental data, making use of a regularization function. The use of this function allows one to build an improved normalization procedure for Monte Carlo spectra, unbiased by the presence of possible new structures in data. We are able to unfold, in a dynamically stable way, data spectra which can be strongly affected by fluctuations in the background subtraction and simultaneously reconstruct structures which were not initially simulated. This method also allows one to control the amount of correlations introduced between the bins of the unfolded spectrum, when the transfers of events correcting the systematic detector effects are performed.Comment: 23 pages, 16 figure

An Iterative, Dynamically Stabilized(IDS) Method of Data Unfolding

We describe an iterative unfolding method for experimental data, making use of a regularization function. The use of this function allows one to build an improved normalization procedure for Monte Carlo spectra, unbiased by the presence of possible new structures in data. We unfold, in a dynamically stable way, data spectra which can be strongly affected by fluctuations in the background subtraction and simultaneously reconstruct structures which were not initially simulated.Comment: 5 pages, 2 figures, presented at PHYSTAT 2011, CERN, Geneva, Switzerland, January 2011, to be published in a CERN Yellow Repor

The Current Status of g-2

Recently, important updates were made for the hadronic contribution to the theoretical prediction of g-2. The isospin-breaking-corrections, needed in the comparison of the two pion spectral functions from tau decays and e+e- annihilations, were improved using new experimental and theoretical input. The recently published BABAR data were included in the global average of e+e- spectral functions. These data, as well as the ones from tau decays, were combined using newly developed software, featuring improved data interpolation and averaging, more accurate error propagation and systematic validation. The discrepancy between the e+e- and the tau-based result is reduced from previously 2.4 to 1.5 sigma. The full Standard Model prediction of g-2, obtained using e+e- data, differs from the experimental value by 3.2 standard deviations.Comment: Two figures remove

Comments on "An Update of the HLS Estimate of the Muon g-2"by M.Benayoun {\it et al.}, arXiv:1210.7184v3

In a recent paper \cite{benayoun} M.Benayoun {\it et al.} use a specific model to compare results on the existing data for the cross section of the process $e^+e^-\rightarrow \pi^+\pi^-$ and state conclusions about the inconsistency of the BABAR results with those from the other experiments. We show that a direct model-independent comparison of the data at hand contradicts this claim. Clear discrepancies with the results of Ref. \cite{benayoun} are pointed out. As a consequence we do not believe that the lower value and the smaller uncertainty obtained for the prediction of the muon magnetic anomaly are reliable results.Comment: 7 pages,2 figures, comment

A note on renormalon models for the determination of alpha_s(M_tau)

The tau hadronic width provides a determination of the strong coupling constant alpha_s at low energies, since it can be related to a weighted integral of the Adler function in the complex energy plane. Using Operator Product Expansion, one sees that the sensitivity to alpha_s comes from the perturbative contribution, which can be obtained by integrating the perturbative expansion of the Adler function. Two different prescriptions proposed to perform this integral, called Fixed-Order Perturbation Theory and Contour-Improved Perturbation Theory (FOPT and CIPT), yield different results for the strong coupling constant. Recently, models for the Adler function based on renormalon calculus have been proposed to determine which of the two methods is the most accurate, by comparing the resulting asymptotic series with the true value of the integral. We discuss the assumptions of such ansatz and the determination of their free parameters. We show that variations of this renormalon ansatz can yield opposite conclusions concerning the comparison of CIPT versus FOPT, and that such models are not constrained enough to provide a definite answer on this issue or to be exploited for a high-precision determination of alpha_s(m_tau^2).Comment: 28 pages, 5 figure