2,564 research outputs found
Bayesian Statistics at Work: the Troublesome Extraction of the CKM Phase alpha
In Bayesian statistics, one's prior beliefs about underlying model parameters
are revised with the information content of observed data from which, using
Bayes' rule, a posterior belief is obtained. A non-trivial example taken from
the isospin analysis of B-->PP (P = pi or rho) decays in heavy-flavor physics
is chosen to illustrate the effect of the naive "objective" choice of flat
priors in a multi-dimensional parameter space in presence of mirror solutions.
It is demonstrated that the posterior distribution for the parameter of
interest, the phase alpha, strongly depends on the choice of the
parameterization in which the priors are uniform, and on the validity range in
which the (un-normalizable) priors are truncated. We prove that the most
probable values found by the Bayesian treatment do not coincide with the
explicit analytical solution, in contrast to the frequentist approach. It is
also shown in the appendix that the alpha-->0 limit cannot be consistently
treated in the Bayesian paradigm, because the latter violates the physical
symmetries of the problem.Comment: 17 pages, 10 figure
Isospin constraints from/on B->pipi
The Standard Model constraints on alpha which can be derived from the B->
pipi decays are revisited in some depth. As experimental inputs, the three
branching ratios, the two CP parameters Spipi and Cpipi and/or the value of
alpha as determined by the global CKM fit are used. The constraints discussed
here are model independent in the sense that they rely only on Isospin
symmetry, following the Gronau-London proposal. A new bound on B00 and the
function C00(B00) are introduced. The Grossman-Quinn bound is rediscussed. A
close form expression is given for alpha as a function of the measurements.
Various scenarii for the future of the isospin analysis are explored. To probe
the Standard Model the (B00,C00) plane is introduced.Comment: 25 pages, 8 figures, Submitted to Eur. Phys. J.
Isospin Breaking Effects in the Extraction of Isoscalar and Isovector Spectral Functions From
We investigate the problem of the extraction of the isovector and isoscalar
spectral functions from data on , in the presence of
non-zero isospin breaking. It is shown that the conventional approach to
extracting the isovector spectral function in the resonance region, in
which only the isoscalar contribution associated with is
subtracted, fails to fully remove the effects of the isoscalar component of the
electromagnetic current. The additional subtractions required to extract the
pure isovector and isoscalar spectral functions are estimated using results
from QCD sum rules. It is shown that the corrections are small () in
the isovector case (though relevant to precision tests of CVC), but very large
() in the case of the contribution to the isoscalar spectral
function. The reason such a large effect is natural in the isoscalar channel is
explained, and implications for other applications, such as the extraction of
the sixth order chiral low-energy constant, , are discussed.Comment: minor changes to introduction, section 2. In Press Phys. Rev.
New high order relations between physical observables in perturbative QCD
We exploit the fact that within massless perturbative QCD the same Green's
function determines the hadronic contribution to the decay width and the
moments of the cross section. This allows one to obtain relations
between physical observables in the two processes up to an unprecedented high
order of perturbative QCD. A precision measurement of the decay width
allows one then to predict the first few moments of the spectral density in
annihilations integrated up to with high accuracy.
The proposed tests are in reach of present experimental capabilities.Comment: 7 pages, Latex, no figure
Test of the Running of in Decays
The decay rate into hadrons of invariant mass smaller than
can be calculated in QCD assuming global
quark--hadron duality. It is shown that this assumption holds for
~GeV. From measurements of the hadronic mass distribution, the
running coupling constant is extracted in the range
0.7~GeV. At , the result is
. The running of is in good
agreement with the QCD prediction.Comment: 9 pages, 3 figures appended; shortened version with new figures, to
appear in Physical Review Letters (April 1996
The Strange Quark Mass From Flavor Breaking in Hadronic Tau Decays
The strange quark mass is extracted from a finite energy sum rule (FESR)
analysis of the flavor-breaking difference of light-light and light-strange
quark vector-plus-axial-vector correlators, using spectral functions determined
from hadronic tau decay data. We point out problems for existing FESR
treatments associated with potentially slow convergence of the perturbative
series for the mass-dependent terms in the OPE over certain parts of the FESR
contour, and show how to construct alternate weight choices which not only cure
this problem, but also (1) considerably improve the convergence of the
integrated perturbative series, (2) strongly suppress contributions from the
region of s values where the errors on the strange current spectral function
are still large and (3) essentially completely remove uncertainties associated
with the subtraction of longitudinal contributions to the experimental decay
distributions. The result is an extraction of m_s with statistical errors
comparable to those associated with the current experimental uncertainties in
the determination of the CKM angle, V_{us}. We find m_s(1 GeV)=158.6\pm 18.7\pm
16.3\pm 13.3 MeV (where the first error is statistical, the second due to that
on V_{us}, and the third theoretical).Comment: 13 pages, 2 figures; final version to appear in Phys. Rev. D;
expanded versions of Figure 2 and Reference 3
The Physics of Hadronic Tau Decays
Hadronic tau decays represent a clean laboratory for the precise study of
quantum chromodynamics (QCD). Observables (sum rules) based on the spectral
functions of hadronic tau decays can be related to QCD quark-level calculations
to determine fundamental quantities like the strong coupling constant,
parameters of the chiral Lagrangian, |V_us|, the mass of the strange quark, and
to simultaneously test the concept of quark-hadron duality. Using the best
available measurements and a revisited analysis of the theoretical framework,
the value alpha_s(m_tau) = 0.345 +- 0.004[exp] +- 0.009[theo] is obtained.
Taken together with the determination of alpha_s(m_Z) from the global
electroweak fit, this result leads to the most accurate test of asymptotic
freedom: the value of the logarithmic slope of 1/alpha_s(s) is found to agree
with QCD at a precision of 4%. In another approach, the tau spectral functions
can be used to determine hadronic quantities that, due to the nonperturbative
nature of long-distance QCD, cannot be computed from first principles. An
example for this is the contribution from hadronic vacuum polarization to
loop-dominated processes like the anomalous magnetic moment of the muon. This
article reviews the measurements of nonstrange and strange tau spectral
functions and their phenomenological applications.Comment: 89 pages, 32 figures; final version accepted for publication by
Reviews of Modern Physic
Remark on the perturbative component of inclusive -decay
In the context of the inclusive -decay, we analyze various forms of
perturbative expansions which have appeared as modifications of the original
perturbative series. We argue that analytic perturbation theory, which combines
renormalization-group invariance and -analyticity, has significant merits
favoring its use to describe the perturbative component of -decay.Comment: 5 pages, ReVTEX, 2 eps figures. Revised paper includes clarifying
remarks and corrected references. To be published in Phys. Rev.
Towards Open Access Publishing in High Energy Physics : Report of the SCOAP3 Working Party
This Report concerns the implementation of a process today supported by leading actors from the particle physics community, and worked through in detail by members of an international Working Party. The initiative offers an opportunity for the cost-effective dissemination of high-quality research articles in particle physics, enabling use of the new technologies of e-Science across the literature of High Energy physics
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