9,759 research outputs found
Measurements of the CKM angle at the B Factories
We report measurements of time-dependent CP asymmetries related to the CKM
angle , using decays of neutral B mesons to charmonium, open
charm and in loop processes. A preliminary measurement of
time-dependent CP asymmetries in decays from the
BaBar experiment is given here.Comment: Contributed to the Proceedings of the XLI Rencontres de Moriond -
Electroweak Interactions and Unified Theory, La Thuile Italy, March 11-18,
2006. 6 page
Scaling regimes in spherical shell rotating convection
Rayleigh-B\'enard convection in rotating spherical shells can be considered
as a simplified analogue of many astrophysical and geophysical fluid flows.
Here, we use three-dimensional direct numerical simulations to study this
physical process. We construct a dataset of more than 200 numerical models that
cover a broad parameter range with Ekman numbers spanning , Rayleigh numbers within the range and a Prandtl number unity. We investigate the scaling behaviours of
both local (length scales, boundary layers) and global (Nusselt and Reynolds
numbers) properties across various physical regimes from onset of rotating
convection to weakly-rotating convection. Close to critical, the convective
flow is dominated by a triple force balance between viscosity, Coriolis force
and buoyancy. For larger supercriticalities, a subset of our numerical data
approaches the asymptotic diffusivity-free scaling of rotating convection
in a narrow fraction of the parameter space delimited by
. Using a decomposition of the viscous
dissipation rate into bulk and boundary layer contributions, we establish a
theoretical scaling of the flow velocity that accurately describes the
numerical data. In rapidly-rotating turbulent convection, the fluid bulk is
controlled by a triple force balance between Coriolis, inertia and buoyancy,
while the remaining fraction of the dissipation can be attributed to the
viscous friction in the Ekman layers. Beyond , the
rotational constraint on the convective flow is gradually lost and the flow
properties vary to match the regime changes between rotation-dominated and
non-rotating convection. The quantity provides an accurate
transition parameter to separate rotating and non-rotating convection.Comment: 42 pages, 20 figures, 3 tables, accepted for publication in JF
CP violation and limits on New Physics including recent measurements
We analyse present constraints on the SM parameter space and derive, in a
model independent way, various bounds on New Physics contributions to
-- and -- mixings. Our analyses include
information on a large set of asymmetries, leading to the measurement of the
CKM phases and , as well as recent data from D0 and CDF
related to the -- system such as the measurement of , and . We examine in detail several
observables such as the asymmetries , , the width differences
and and discuss the r\^ole they play
in establishing the limits on New Physics. The present data clearly favour the
SM, with the New Physics favoured region placed around the SM solution. A New
Physics solution significantly different from the SM is still allowed, albeit
quite disfavoured (2.6% probability). We analyse the presently available
indirect knowledge on the phase entering in --
mixing and study the impact of a future measurement of to be
achieved at LHC, through the measurement of the time-dependent CP asymmetry in
decays.Comment: 29 pages, 31 figures; updated analyses and reference
Time Reversal Violation from the entangled B0-antiB0 system
We discuss the concepts and methodology to implement an experiment probing
directly Time Reversal (T) non-invariance, without any experimental connection
to CP violation, by the exchange of "in" and "out" states. The idea relies on
the B0-antiB0 entanglement and decay time information available at B factories.
The flavor or CP tag of the state of the still living neutral meson by the
first decay of its orthogonal partner overcomes the problem of irreversibility
for unstable systems, which prevents direct tests of T with incoherent particle
states. T violation in the time evolution between the two decays means
experimentally a difference between the intensities for the time-ordered (l^+
X, J/psi K_S) and (J/psi K_L, l^- X) decays, and three other independent
asymmetries. The proposed strategy has been applied to simulated data samples
of similar size and features to those currently available, from which we
estimate the significance of the expected discovery to reach many standard
deviations.Comment: 17 pages, 2 figures, 6 table
Comment on form factor shape and extraction of |V_ub| from B --> pi l nu
We point out that current experimental data for partial B --> pi l nu
branching fractions reduce the theoretical input required for a precise
extraction of |V_ub| to the form factor normalization at a single value of the
pion energy. We show that the heavy-quark expansion provides a bound on the
form factor shape that is orders of magnitude more stringent than conventional
unitarity bounds. We find |V_ub| = (3.7 +/- 0.2 +/- 0.1) x [0.8/F_+(16 GeV^2)].
The first error is from the experimental branching fractions, and the second is
a conservative bound on the residual form factor shape uncertainty, both of
which will improve with additional data. Together with current and future
lattice determinations of the form factor normalization this result gives an
accurate, model independent determination of |V_ub|. We further extract
semileptonic shape observables such as |V_ub F_+(0)| = 0.92 +/- 0.11 +/- 0.03
and show how these observables can be used to test factorization and to
determine low-energy parameters in hadronic B decays.Comment: 14 pages, 3 figures; journal version, results and conclusions
unchange
Too many , and ?
A large number of new states have been reported during the last few years in
charmonium spectroscopy above the charmed meson production threshold. They have
been called , , and . We reflect on the influence of thresholds
on heavy meson spectroscopy comparing different flavor sectors and quantum
numbers. The validity of a quark-model picture above open-flavor thresholds
would severely restrict the number of channels that may lodge meson-meson
molecules.Comment: 8 pages, 5 figure
Inferring internal properties of Earth's core dynamics and their evolution from surface observations and a numerical geodynamo model
Over the past decades, direct three-dimensional numerical modelling has been successfully used to reproduce the main features of the geodynamo. Here we report on efforts to solve the associated inverse problem, aiming at inferring the underlying properties of the system from the sole knowledge of surface observations and the first principle dynamical equations describing the convective dynamo. To this end we rely on twin experiments. A reference model time sequence is first produced and used to generate synthetic data, restricted here to the large-scale component of the magnetic field and its rate of change at the outer boundary. Starting from a different initial condition, a second sequence is next run and attempts are made to recover the internal magnetic, velocity and buoyancy anomaly fields from the sparse surficial data. In order to reduce the vast underdetermination of this problem, we use stochastic inversion, a linear estimation method determining the most likely internal state compatible with the observations and some prior knowledge, and we also implement a sequential evolution algorithm in order to invert time-dependent surface observations. The prior is the multivariate statistics of the numerical model, which are directly computed from a large number of snapshots stored during a preliminary direct run. The statistics display strong correlation between different harmonic degrees of the surface observations and internal fields, provided they share the same harmonic order, a natural consequence of the linear coupling of the governing dynamical equations and of the leading influence of the Coriolis force. Synthetic experiments performed with a weakly nonlinear model yield an excellent quantitative retrieval of the internal structure. In contrast, the use of a strongly nonlinear (and more realistic) model results in less accurate static estimations, which in turn fail to constrain the unobserved small scales in the time integration of the evolution scheme. Evaluating the quality of forecasts of the system evolution against the reference solution, we show that our scheme can improve predictions based on linear extrapolations on forecast horizons shorter than the system <i>e</i>-folding time. Still, in the perspective of forthcoming data assimilation activities, our study underlines the need of advanced estimation techniques able to cope with the moderate to strong nonlinearities present in the geodynamo
Graded Hecke algebras for disconnected reductive groups
We introduce graded Hecke algebras H based on a (possibly disconnected)
complex reductive group G and a cuspidal local system L on a unipotent orbit of
a Levi subgroup M of G. These generalize the graded Hecke algebras defined and
investigated by Lusztig for connected G.
We develop the representation theory of the algebras H. obtaining complete
and canonical parametrizations of the irreducible, the irreducible tempered and
the discrete series representations. All the modules are constructed in terms
of perverse sheaves and equivariant homology, relying on work of Lusztig. The
parameters come directly from the data (G,M,L) and they are closely related to
Langlands parameters.
Our main motivation for considering these graded Hecke algebras is that the
space of irreducible H-representations is canonically in bijection with a
certain set of "logarithms" of enhanced L-parameters. Therefore we expect these
algebras to play a role in the local Langlands program. We will make their
relation with the local Langlands correspondence, which goes via affine Hecke
algebras, precise in a sequel to this paper.Comment: Theorem 3.4 and Proposition 3.22 in version 1 were not entirely
correct as stated. This is repaired in a new appendi
Nonleptonic charmless two-body decays
In this work we have studied hadronic charmless two-body B decays involving
p-wave mesons in final state. We have calculated branching ratios of
decays (where and denotes a axial-vector and a tensor meson,
respectively), using form factors obtained in the covariant
light-front (CLF) approach, and the full effective Hamiltonian. We have
obtained that ,
,
(with ) for ,
with
, for
where . It seems that these decays can be measured
in experiments at factories. Additionally, we have found that
and
ratios could be useful to determine numerical values of mixing angles
and , respectively.Comment: 12 page
The UTfit Collaboration Average of D meson mixing data: Spring 2012
We derive constraints on the parameters , and
that describe meson mixing using all available data, allowing
for CP violation. We also provide posterior distributions and predictions for
observable parameters appearing in physics.Comment: 5 pages, 3 figure
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