2,409 research outputs found

    Determination of MbM_b and αs\alpha_s from the Upsilon System

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    The mass of the bottom quark (both the pole mass MbM_b and the \MSb mass mbm_b) and the strong coupling constant αs\alpha_s have been determined from QCD moment sum rules for the Υ\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 αs(MZ)=0.119±0.008\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

    Spectral distribution for the decay tau -> nu_tau K pi

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    With the newly available data sets on hadronic tau decays from the B-factories BABAR and BELLE, and future data from BESIII, precise information on the decay distributions will soon become available. This calls for an improvement of the decay spectra also on the theoretical side. In this work, the distribution function for the decay tau -> nu_tau K pi will be presented with the relevant K pi vector and scalar form factors being calculated in the framework of the resonance chiral theory, also taking into account additional constraints from dispersion relations and short-distances. As a by-product the slope and curvature of the vector form factor F_+^{K pi}(s) are determined to be lambda_+^' = 25.6 10^{-3} and lambda_+^{''} = 1.31 10^{-3} respectively. From our approach it appears that it should be possible to obtain information on the low lying scalar K_0^*(800) as well as the second vector K^*(1410) resonances from the tau decay data. In particular, the exclusive branching fraction of the scalar component is found to be B[tau -> nu_tau(K pi)_{S-wave}] = (3.88 +- 0.19) 10^{-4}.Comment: 14 pages, 2 figure

    Combined analysis of the decays τKSπντ\tau^-\to K_S\pi^-\nu_\tau and τKηντ\tau^-\to K^-\eta\nu_\tau

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    In a combined study of the decay spectra of τKSπντ\tau^-\to K_S\pi^-\nu_\tau and τKηντ\tau^-\to K^-\eta\nu_\tau decays within a dispersive representation of the required form factors, we illustrate how the K(1410)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 MK=1304±17M_{K^{*\prime}}=1304 \pm 17\,MeV and ΓK=171±62\Gamma_{K^{*\prime}} = 171 \pm 62\,MeV. Further constraints on the width could result from updated analyses of the KπK\pi and/or KηK\eta spectra using the full Belle-I data sample. Prospects for Belle-II are also discussed. As the Kπ0K^-\pi^0 vector form factor enters the description of the decay τKηντ\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 τKπ0ντ\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

    Determination of |V_us| from hadronic tau decays

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    The recent update of the strange spectral function and the moments of the invariant mass distribution by the OPAL collaboration from hadronic tau decay data are employed to determine |V_us| as well as m_s. Our result, |V_us|=0.2208\pm0.0034, is competitive to the standard extraction of |V_us| from K_e3 decays and to the new proposals to determine it. Furthermore, the error associated to our determination of |V_us| can be reduced in the future since it is dominated by the experimental uncertainty that will be eventually much improved by the B-factories hadronic tau data. Another improvement that can be performed is the simultaneous fit of both |V_us| and m_s to a set of moments of the hadronic tau decays invariant mass distribution, which will provide even a more accurate determination of both parameters.Comment: 6 pages. Invited talk given by E.G. at the XXXXth Rencontres de Moriond on Electroweak Interactions and Unified Theories, La Thuile, Italy, 5-12 Mar 200

    Final State Interactions in Hadronic D decays

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    We show that the large corrections due to final state interactions (FSI) in the D^+\to \pi^-\pi^+\pi^+, D^+_s\to \pi^-\pi^+\pi^+, and D^+\to K^-\pi^+\pi^+ decays can be accounted for by invoking scattering amplitudes in agreement with those derived from phase shifts studies. In this way, broad/overlapping resonances in S-waves are properly treated and the phase motions of the transition amplitudes are driven by the corresponding scattering matrix elements determined in many other experiments. This is an important step forward in resolving the puzzle of the FSI in these decays. We also discuss why the \sigma and \kappa resonances, hardly visible in scattering experiments, are much more prominent and clearly visible in these decays without destroying the agreement with the experimental \pi\pi and K\pi low energy S-wave phase shifts.Comment: 22 pages, 6 figures, 5 tables. Minor changes. We extend the discusion when quoting a reference and we include a new one. Some typos are fixe

    alpha_s from tau decays revisited

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    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

    Duality Violation and the K --> pi pi Electroweak Penguin Operator Matrix Elements from Hadronic Tau Decays

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    We discuss a preliminary study of the impact of duality violations on extractions from tau decay data of the D=6 VEVs which determine chiral limit Standard Model K-->pi pi matrix elements of the electroweak penguin operators.Comment: 4 pages, 5 figures, prepared for the Proceedings of the 11th Particle and Nuclear Intersections Conference (PANIC 2011), Boston, USA, July 24-29, 201

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

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    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]
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