Determination of MbM_b and αs\alpha_s from the Upsilon System

The mass of the bottom quark (both the pole mass $M_b$ and the \MSb mass $m_b$) and the strong coupling constant $\alpha_s$ have been determined from QCD moment sum rules for the $\Upsilon$ system. In the pole-mass scheme large perturbative corrections resulting from coulombic contributions have been resummed. The results of this analysis are: M_b=4.60 \pm 0.02 \gev, m_b(m_b)=4.13 \pm 0.06 \gev and $\alpha_s(M_Z)=0.119 \pm 0.008$.Comment: 5 pages, 1 Postscript figure Invited talk at the High Energy Conference on Quantum Chromodynamics (QCD'97), Montpellier, July 199

alpha_s from tau decays revisited

Being a determination at low energies, the analysis of hadronic tau decay data provides a rather precise determination of the strong coupling alpha_s after evolving the result to M_Z. At such a level of precision, even small non-perturbative effects become relevant for the central value and error. While those effects had been taken into account in the framework of the operator product expansion, contributions going beyond it, so-called duality violations, have previously been neglected. The following investigation fills this gap through a finite-energy sum rule analysis of tau decay spectra from the OPAL experiment, including duality violations and performing a consistent fit of all appearing QCD parameters. The resulting values for alpha_s(M_tau) are 0.307(19) in fixed-order perturbation theory and 0.322(26) in contour-improved perturbation theory, which translates to the n_f=5 values 0.1169(25) and 0.1187(32) at M_Z, respectively.Comment: 4 pages, 3 figures. Prepared for the Proceedings of the International Workshop on e+e- collisions from Phi to Psi (PHIPSI11), Sep. 19-22, 2011, BINP, Novosibirsk, Russi

Flavour-symmetry breaking of the quark condensate and chiral corrections to the Gell-Mann-Oakes-Renner relation

The relation between the chiral quark condensate in QCD sum rules and chiral perturbation theory is clarified with the help of a low-energy theorem for the scalar and pseudoscalar correlation functions. It is found that the quark condensate should be identified with the non-normal-ordered vacuum expectation value of quark-antiquark fields. Utilising results on flavour SU(3) breaking of the quark condensate from QCD sum rules, the unphysical low-energy constant H_2^r in the chiral Lagrangian, as well as next-to-leading order corrections to the Gell-Mann-Oakes-Renner relation are estimated

Semileptonic D decay into scalar mesons: a QCD sum rule approach

Semileptonic decays of D-mesons into scalar hadronic states are investigated. Two extreme cases are considered: a) the meson decays directly into an uncorrelated scalar state of two two mesons and b) the decay proceeds via resonance formation. QCD sum rules including instanton contributions are used to calculate total and differential decay rates under the two assumptions.Comment: 18 pages, 9 figures, e-mail: [email protected]

Combined analysis of the decays τ−→KSπ−ντ\tau^-\to K_S\pi^-\nu_\tau and τ−→K−ηντ\tau^-\to K^-\eta\nu_\tau

In a combined study of the decay spectra of $\tau^-\to K_S\pi^-\nu_\tau$ and $\tau^-\to K^-\eta\nu_\tau$ decays within a dispersive representation of the required form factors, we illustrate how the $K^*(1410)$ resonance parameters, defined through the pole position in the complex plane, can be extracted with improved precision as compared to previous studies. While we obtain a substantial improvement in the mass, the uncertainty in the width is only slightly reduced, with the findings $M_{K^{*\prime}}=1304 \pm 17\,$MeV and $\Gamma_{K^{*\prime}} = 171 \pm 62\,$MeV. Further constraints on the width could result from updated analyses of the $K\pi$ and/or $K\eta$ spectra using the full Belle-I data sample. Prospects for Belle-II are also discussed. As the $K^-\pi^0$ vector form factor enters the description of the decay $\tau^-\to K^-\eta\nu_\tau$, we are in a position to investigate isospin violations in its parameters like the form factor slopes. In this respect also making available the spectrum of the transition $\tau^-\to K^-\pi^0\nu_\tau$ would be extremely useful, as it would allow to study those isospin violations with much higher precision.Comment: 20 pages, 1figur

Bayesian approach to the first excited nucleon state in lattice QCD

We present preliminary results from the first attempt to reconstruct the spectral function in the nucleon and $\Delta$ channels from lattice QCD data using the maximum entropy method (MEM). An advantage of the MEM analysis is to enable us to access information of the excited state spectrum. Performing simulations on two lattice volumes, we confirm the large finite size effect on the first excited nucleon state in the lighter quark mass region.Comment: Lattice2002(spectrum), Latex with espcrc2.sty, 3 pages, 3 figure

Virtual O(\a_s) corrections to the inclusive decay b→sγb \to s \gamma

We present in detail the calculation of the O(\a_s) virtual corrections to the matrix element for b \to s \g. Besides the one-loop virtual corrections of the electromagnetic and color dipole operators $O_7$ and $O_8$, we include the important two-loop contribution of the four-Fermi operator $O_2$. By applying the Mellin-Barnes representation to certain internal propagators, the result of the two-loop diagrams is obtained analytically as an expansion in $m_c/m_b$. These results are then combined with existing O(\a_s) Bremsstrahlung corrections in order to obtain the inclusive rate for B \to X_s \g. The new contributions drastically reduce the large renormalization scale dependence of the leading logarithmic result. Thus a very precise Standard Model prediction for this inclusive process will become possible once also the corrections to the Wilson coefficients are available.Comment: 29 pages, uses epsfig.sty, 12 postscript figures include

epsilon'/epsilon at the NLO: 10 Years Later

During the last four years several parameters relevant for the analysis of the CP-violating ratio epsilon'/epsilon improved and/or changed significantly. In particular, the experimental value of epsilon'/epsilon and the strange quark mass decreased, the uncertainty in the CKM factor has been reduced, and for a value of the hadronic matrix element of the dominant electroweak penguin operator Q_8, some consensus has been reached among several theory groups. In view of this situation, ten years after the first analyses of epsilon'/epsilon at the next-to-leading order, we reconsider the analysis of epsilon'/epsilon within the SM and investigate what can be said about the hadronic Q_6 matrix element of the dominant QCD penguin operator on the basis of the present experimental value of epsilon'/epsilon and todays values of all other parameters. Employing a conservative range for the reduced electroweak penguin matrix element R_8=1.0+-0.2 from lattice QCD, and present values for all other input parameters, on the basis of the current world average for epsilon'/epsilon, we obtain the reduced hadronic matrix element of the dominant QCD penguin operator R_6=1.23+-0.16 implying _0^NDR(m_c) ~ -0.8 _2^NDR(m_c). We compare these results with those obtained in large-N_c approaches in which generally R_6 ~ R_8 and _0^NDR(m_c) is chirally suppressed relatively to _2^NDR(m_c). We present the correlation between R_6 and R_8 that is implied by the data on epsilon'/epsilon provided new physics contributions to epsilon'/epsilon can be neglected.Comment: 18 pages, 1 eps figure, version to appear in JHE