5,170 research outputs found
Reply to: ''Improved Determination of the CKM Angle alpha from B -> pipi decays''
In reply to hep-ph/0701204 we demonstrate why the arguments made therein do
not address the criticism exposed in hep-ph/0607246 on the fundamental
shortcomings of the Bayesian approach when it comes to the extraction of
parameters of Nature from experimental data. As for the isospin analysis and
the CKM angle alpha it is shown that the use of uniform priors for the observed
quantities in the Explicit Solution parametrization is equivalent to a
frequentist construction resulting from a change of variables, and thus relies
neither on prior PDFs nor on Bayes' theorem. This procedure provides in this
particular case results that are similar to the Confidence Level approach, but
the treatment of mirror solutions remains incorrect and it is far from being
general. In a second part it is shown that important differences subsist
between the Bayesian and frequentist approaches, when following the proposal of
hep-ph/0701204 and inserting additional information on the hadronic amplitudes
beyond isospin invariance. In particular the frequentist result preserves the
exact degeneracy that is expected from the remaining symmetries of the problem
while the Bayesian procedure does not. Moreover, in the Bayesian approach
reducing inference to the 68% or 95% credible interval is a misconception of
the meaning of the posterior PDF, which in turn implies that the significant
dependence of the latter to the chosen parametrization cannot be viewed as a
minor effect, contrary to the claim in hep-ph/0701204.Comment: 5 pages, 1 figure. Fig. 1 corrected (wrong file
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
Towards a global fit to extract the B->Xs gamma decay rate and Vub
The total B->Xs gamma decay rate and the CKM-matrix element Vub play an
important role in finding indirect evidence for new physics affecting the
flavor sector of the Standard Model, complementary to direct searches at the
LHC and Tevatron. Their determination from inclusive B-meson decays requires
the precise knowledge of the parton distribution function of the b quark in the
B meson, called the shape function. We implement a new model-independent
framework for the shape function with reliable uncertainties based on an
expansion in a suitable set of basis functions. We present the current status
of a global fit to BaBar and Belle data to extract the shape function and the
B->Xs gamma decay rate.Comment: 5 pages, 9 figure
A model independent determination of the B -> Xs gamma decay rate
The goal of the SIMBA collaboration is to provide a global fit to the
available measurements of inclusive B -> X_s gamma and B -> X_u l nu decays. By
performing a global fit one is able to simultaneously determine the relevant
normalizations, i.e. the total B -> X_s gamma rate and the CKM-matrix element
|Vub|, together with the required hadronic parameters, most importantly the
b-quark mass and the b-quark distribution function in the B-meson, called the
shape function. In this talk, the current status on the model-independent
determination of the shape function and |C7^\incl Vtb Vts*|, which parametrizes
the total B -> Xs gamma rate, from a global fit to the available B -> X_s gamma
measurements from Babar and Belle is presented. In particular, the theoretical
uncertainties originating from variations of the different factorization scales
are evaluated.Comment: Proceedings of CKM 2012, the 7th International Workshop on the CKM
Unitarity Triangle, University of Cincinnati, USA, 28 September - 2 October
201
Predictions of selected flavour observables within the Standard Model
This letter gathers a selection of Standard Model predictions issued from the
metrology of the CKM parameters performed by the CKMfitter group. The selection
includes purely leptonic decays of neutral and charged B, D and K mesons. In
the light of the expected measurements from the LHCb experiment, a special
attention is given to the radiative decay modes of B mesons as well as to the
B-meson mixing observables, in particular the semileptonic charge asymmetries
a^d,s_SL which have been recently investigated by the D0 experiment at
Tevatron. Constraints arising from rare kaon decays are addressed, in light of
both current results and expected performances of future rare kaon experiments.
All results have been obtained with the CKMfitter analysis package, featuring
the frequentist statistical approach and using Rfit to handle theoretical
uncertainties.Comment: 8 pages, 1 figure, 2 tables. Typos corrected and discussion of
agreement between SM and data update
Analysing powers for the reaction and for np elastic scattering from 270 to 570 MeV
The analysing power of the reaction for neutron energies between threshold and 570 MeV has been determined
using a transversely polarised neutron beam at PSI. The reaction has been
studied in a kinematically complete measurement using a time-of-flight
spectrometer with large acceptance. Analysing powers have been determined as a
function of the c.m. pion angle in different regions of the proton-proton
invariant mass. They are compared to other data from the reactions and . The np elastic scattering analysing power was determined as a
by-product of the measurements.Comment: 12 pages, 6 figures, subitted to EPJ-
The reaction from threshold up to 570 MeV
The reaction has been studied in a
kinematically complete measurement with a large acceptance time-of-flight
spectrometer for incident neutron energies between threshold and 570 MeV. The
proton-proton invariant mass distributions show a strong enhancement due to the
pp() final state interaction. A large anisotropy was found in the
pion angular distributions in contrast to the reaction . At small energies, a large forward/backward asymmetry has been
observed. From the measured integrated cross section , the isoscalar cross section has been extracted.
Its energy dependence indicates that mainly partial waves with Sp final states
contribute. Note: Due to a coding error, the differential cross sections as shown in Fig. 9 are too small by a factor of two, and
inn Table 3 the differential cross sections
are too large by a factor of . The integrated cross sections and all
conclusions remain unchanged. A corresponding erratum has been submitted and
accepted by European Physics Journal.Comment: 18 pages, 16 figure
Master equation approach to friction at the mesoscale
At the mesoscale friction occurs through the breaking and formation of local
contacts. This is often described by the earthquake-like model which requires
numerical studies. We show that this phenomenon can also be described by a
master equation, which can be solved analytically in some cases and provides an
efficient numerical solution for more general cases. We examine the effect of
temperature and aging of the contacts and discuss the statistical properties of
the contacts for different situations of friction and their implications,
particularly regarding the existence of stick-slip.Comment: To be published in Physical Review
Model-independent extraction of matrix elements from top-quark measurements at hadron colliders
Current methods to extract the quark-mixing matrix element from
single-top production measurements assume that : top quarks decay into quarks with 100% branching fraction,
s-channel single-top production is always accompanied by a quark and
initial-state contributions from and quarks in the -channel
production of single top quarks are neglected. Triggered by a recent
measurement of the ratio
performed by the D0 collaboration, we consider a extraction method
that takes into account non zero d- and s-quark contributions both in
production and decay. We propose a strategy that allows to extract consistently
and in a model-independent way the quark mixing matrix elements ,
, and from the measurement of and from single-top
measured event yields. As an illustration, we apply our method to the Tevatron
data using a CDF analysis of the measured single-top event yield with two jets
in the final state one of which is identified as a -quark jet. We constrain
the matrix elements within a four-generation scenario by combining
the results with those obtained from direct measurements in flavor physics and
determine the preferred range for the top-quark decay width within different
scenarios.Comment: 36 pages, 17 figure
Status of SIMBA
The goal of the SIMBA collaboration is to provide a global fit to the available data in inclusive B -> X_s gamma and B -> X_u l nu decays. By performing a global fit one is able to simultaneously determine the relevant normalizations, i.e. the total B -> X_s gamma rate and the CKM-matrix element |Vub|, together with the required input parameters, most importantly the b-quark mass and the b-quark distribution function in the B-meson, called the shape function. This strategy is analogous to the determination of |Vcb| from global fits to inclusive B -> X_c l nu decays. In this talk, we present preliminary results for the shape function and |C_7^incl Vtb Vts^*|, which parametrizes the total B -> X_s gamma rate, from a global fit to the available B -> X_s gamma measurements from BABAR and Belle
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