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Diogo Boito

Publications and source records attributed to Diogo Boito.

61 records · Page 4Linked to original sources
arXiv2013

On the perturbative expansion of tau hadronic spectral function moments

In the determination of alpha_s from tau decays several different moments of the hadronic spectral functions have been used. In a recent work, we performed an analysis of their perturbative behaviour under two different assumptions for the higher-order coefficients of the Adler function. We showed that the various moments can be divided in a small number of classes. We concluded that some of the moments commonly employed in alpha_s extractions should be avoided due to their bad perturbative behaviour. Furthermore, for the moments that have a good perturbative behaviour, and under reasonable assumptions for the higher-order behaviour of the Adler function, fixed-order perturbation theory (FOPT) provides the superior framework for the renormalization group improvement. Here we discuss an extension of this analysis where we consider the perturbative series for values of the hadronic invariant mass squared s_0 < m_τ^2. Our conclusions are not altered within a reasonable s_0 window.

hep-ph↗
arXiv2012

The strong coupling from tau decays without prejudice

We review our recent determination of the strong coupling α_s from the OPAL data for non-strange hadronic tau decays. We find that α_s(m^2_τ) =0.325+-0.018 using fixed-order perturbation theory, and α_s(m^2_τ)=0.347+-0.025 using contour-improved perturbation theory. At present, these values supersede any earlier determinations of the strong coupling from hadronic tau decays, including those from ALEPH data.

hep-ph↗
arXiv2012

Perturbative expansion of tau hadronic spectral function moments and alpha_s extractions

Various moments of the hadronic spectral functions have been employed in the determination of the strong coupling alpha_s from tau decays. In this work we study the behaviour of their perturbative series under different assumptions for the large-order behaviour of the Adler function, extending previous work on the tau hadronic width. We find that the moments can be divided into a small number of classes, whose characteristics depend only on generic features of the moment weight function and Adler function series. Some moments that are commonly employed in alpha_s analyses from tau decays should be avoided because of their perturbative instability. This conclusion is corroborated by a simplified alpha_s extraction from individual moments. Furthermore, under reasonable assumptions for the higher-order behaviour of the perturbative series, fixed-order perturbation theory (FOPT) provides the preferred framework for the renormalization group improvement of all moments that show good perturbative behaviour. Finally, we provide further evidence for the plausibility of the description of the Adler function in terms of a small number of leading renormalon singularities.

hep-ph↗
arXiv2012

An updated determination of α_s from tau decays

Employing our previous framework to treat non-perturbative effects self-consistently, including duality violations, we update the determination of the strong coupling, α_s, using a modified version of the 1998 OPAL data, updated to reflect current values of exclusive mode hadronic τdecay branching fractions. Our best n_f=3 values from the updated OPAL data are α_s(m^2_τ)=0.325+-0.018 and α_s(m^2_τ)=0.347+-0.025 in fixed-order and contour-improved perturbation theory, respectively. To account for non-perturbative effects, non-linear, multi-parameter fits are necessary. We have, therefore, investigated the posterior probability distribution of the model parameters underlying our fits in more detail. We find that OPAL data alone provide only weak constraints on some of the parameters needed to model duality violations, especially in the case of fits involving axial vector channel data, making additional prior assumptions on the expected size of these parameters necessary at present. We provide evidence that this situation could be greatly improved if hadronic spectral functions based on the high-statistics BaBar and Belle data were to be made available.

hep-ph↗
arXiv2011

On the Extraction of the Strong Coupling from Hadronic Tau Decay

The finite energy sum rule extraction of the strong coupling α_s from hadronic τ decay data provides one of its most precise experimental determinations. As precision improves, small non-perturbative effects become increasingly relevant to both the central value and error. Here we present a new framework for this extraction employing a physically motivated model to accommodate violations of quark-hadron duality and enforcing a consistent treatment of higher-dimension operator product expansion contributions. Using 1998 OPAL data for the non-strange vector and axial-vector spectral functions, we find the n_f=3 values for α_s(m_τ^2) of 0.307(19) for fixed-order perturbation theory and 0.322(26) for contour-improved perturbation theory, corresponding to n_f=5 values for α_s(M_Z^2) of 0.1169(25) and 0.1187(32), respectively.

hep-lat↗
arXiv2011

A new determination of α_s from hadronic τ decays

We present a new framework for the extraction of the strong coupling from hadronic τdecays through finite-energy sum rules. Our focus is on the small, but still significant non-perturbative effects that, in principle, affect both the central value and the systematic error. We employ a quantitative model in order to accommodate violations of quark-hadron duality, and enforce a consistent treatment of the higher-dimensional contributions of the Operator Product Expansion to our sum rules. Using 1998 OPAL data for the non-strange isovector vector and axial-vector spectral functions, we find the n_f=3 values α_s(m_τ^2)=0.307+-0.019 in fixed-order perturbation theory, and 0.322+-0.026 in contour-improved perturbation theory. For comparison, the original OPAL analysis of the same data led to the values 0.324+-0.014 (fixed-order) and 0.348+-0.021 (contour-improved).

hep-ph↗