2,409 research outputs found

### Determination of $M_b$ and $\alpha_s$ 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

### Spectral distribution for the decay tau -> nu_tau K pi

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 $\tau^-\to K_S\pi^-\nu_\tau$ and $\tau^-\to K^-\eta\nu_\tau$

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

### Determination of |V_us| from hadronic tau decays

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

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

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

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

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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