6,166 research outputs found

### Charm Meson Spectroscopy at Babar and CLEO-C

In this mini-review we report on the most recent progress in charm meson
spectroscopy. We discuss the precision measurements performed by the BaBar and
CLEO-c experiments in the non strange charm meson part and we present the newly
discovered strange charmed meson excited states.Comment: To be published in the proceedings of CHARM07, Ithaca, NY, August
2007, eConf C070805 First version had an unecessary additional tex file
(containing symbols) which has been added to the pdf fil

### Hadronic B decays at BABAR

By means of hadronic B decays, the BABAR experiment aims to constrain the CKM matrix performing CP parameter measurements. It also seeks to test QCD factorization predictions and other models for B structure and decay mechanisms. We will present some of the on-going CP related analyses in the first section, while the second section will be dedicated to report on the conducted investigations on subjects as diverse as probing the gluon component in the B meson wave function, new physics and final state interactions in annihilation processes, intrinsic charm searches and first observation of strange charmed baryon production in B decays

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### Hadronic B Decays at BaBar

By means of hadronic B decays, the BABAR experiment aims to constrain the CKM matrix performing CP parameter measurements. It also seeks to test QCD factorization predictions and other models for B structure and decay mechanisms. We will present some of the on-going CP related analyses in the first section, while the second section will be dedicated to report on the conducted investigations on subjects as diverse as probing the gluon component in the B meson wave function, new physics and final state interactions in annihilation processes, intrinsic charm searches and first observation of strange charmed baryon production in B decays

### Longitudinal response function of 4He with a realistic force

The longitudinal response function of 4He is calculated with the Argonne V18
potential. The comparison with experiment suggests the need of a three-body
force. When adding the Urbana IX three-body potential in the calculation of the
lower longitudinal multipoles, the total strength is suppressed in the
quasi-elastic peak, towards the trend of the experimental data.Comment: 3 pages, 3 figures, proceedings of the 20th European Conference on
Few-Body Problems in Physics (EFB20

### Focusing of high-energy particles in the electrostatic field of a homogeneously charged sphere and the effective momentum approximation

The impact of the strongly attractive electromagnetic field of heavy nuclei
on electrons in quasi-elastic (e,e') scattering is often accounted for by the
effective momentum approximation. This method is a plane wave Born
approximation which takes the twofold effect of the attractive nucleus on
initial and final state electrons into account, namely the modification of the
electron momentum in the vicinity of the nucleus, and the focusing of electrons
towards the nuclear region leading to an enhancement of the corresponding wave
function amplitudes. The focusing effect due to the attractive Coulomb field of
a homogeneously charged sphere on a classical ensemble of charged particles
incident on the field is calculated in the highly relativistic limit and
compared to results obtained from exact solutions of the Dirac equation. The
result is relevant for the theoretical foundation of the effective momentum
approximation and describes the high energy behavior of the amplitude of
continuum Dirac waves in the potential of a homogeneously charged sphere. Our
findings indicate that the effective momentum approximation is a useful
approximation for the calculation of Coulomb corrections in (e,e') scattering
off heavy nuclei for sufficiently high electron energies and momentum transfer.Comment: 16 pages, 9 figures, LATEX, some references adde

### Exact 4He Spectral Function in a Semirealistic NN Potential Model

The spectral function of 4He is calculated with the Lorentz integral
transform method in a large energy and momentum range. The excitation spectrum
of the residual 3N-system is fully taken into account. The obtained spectral
function is used to calculate the quasi elastic longitudinal (e,e') response
R_l of 4He for q=300, 400, and 500 MeV/c. Comparison with the exact R_l shows a
rather sizeable disagreement except in the quasi elastic peak, where the
differences reduce to about 10% at q=500 MeV/c. It is shown as well that very
simple momentum distribution approximations for the spectral function provide
practically the same results for R_l as the exact spectral function.Comment: 7 pages, Latex (Revtex), 4 Postscript figures, to appear in Phys.
Rev.

### Approximate treatment of electron Coulomb distortion in quasielastic (e,e') reactions

In this paper we address the adequacy of various approximate methods of
including Coulomb distortion effects in (e,e') reactions by comparing to an
exact treatment using Dirac-Coulomb distorted waves. In particular, we examine
approximate methods and analyses of (e,e') reactions developed by Traini et al.
using a high energy approximation of the distorted waves and phase shifts due
to Lenz and Rosenfelder. This approximation has been used in the separation of
longitudinal and transverse structure functions in a number of (e,e')
experiments including the newly published 208Pb(e,e') data from Saclay. We find
that the assumptions used by Traini and others are not valid for typical (e,e')
experiments on medium and heavy nuclei, and hence the extracted structure
functions based on this formalism are not reliable. We describe an improved
approximation which is also based on the high energy approximation of Lenz and
Rosenfelder and the analyses of Knoll and compare our results to the Saclay
data. At each step of our analyses we compare our approximate results to the
exact distorted wave results and can therefore quantify the errors made by our
approximations. We find that for light nuclei, we can get an excellent
treatment of Coulomb distortion effects on (e,e') reactions just by using a
good approximation to the distorted waves, but for medium and heavy nuclei
simple additional ad hoc factors need to be included. We describe an explicit
procedure for using our approximate analyses to extract so-called longitudinal
and transverse structure functions from (e,e') reactions in the quasielastic
region.Comment: 30 pages, 8 figures, 16 reference

### Eikonal analysis of Coulomb distortion in quasi-elastic electron scattering

An eikonal expansion is used to provide systematic corrections to the eikonal
approximation through order $1/k^2$, where $k$ is the wave number. Electron
wave functions are obtained for the Dirac equation with a Coulomb potential.
They are used to investigate distorted-wave matrix elements for quasi-elastic
electron scattering from a nucleus. A form of effective-momentum approximation
is obtained using trajectory-dependent eikonal phases and focusing factors.
Fixing the Coulomb distortion effects at the center of the nucleus, the
often-used ema approximation is recovered. Comparisons of these approximations
are made with full calculations using the electron eikonal wave functions. The
ema results are found to agree well with the full calculations.Comment: 12 pages, 6 Postscript figure

### Eta-Helium Quasi-Bound States

The cross section and tensor analysing power t_20 of the d\vec{d}->eta 4He
reaction have been measured at six c.m. momenta, 10 < p(eta) < 90 MeV/c. The
threshold value of t_20 is consistent with 1/\sqrt{2}, which follows from
parity conservation and Bose symmetry. The much slower momentum variation
observed for the reaction amplitude, as compared to that for the analogous
pd->eta 3He case, suggests strongly the existence of a quasi-bound state in the
eta-4He system and optical model fits indicate that this probably also the case
for eta-3He.Comment: LaTeX, uses elsart.sty, 10 pages, 3 Postscript figures, Submitted to
Physics Letters

### Mean-field calculations of quasi-elastic responses in 4He

We present calculations of the quasi-elastic responses functions in 4He based
upon a mean-field model used to perform analogous calculations in heavier
nuclei. The meson exchange current contribution is small if compared with the
results of calculations where short-range correlations are explicitly
considered. It is argued that the presence of these correlations in the
description of the nuclear wave functions is crucial to make meson exchange
current effects appreciable.Comment: uuencoded file containing 7 LaTex peges plus 3 ps figures. To be
published in Physical Review

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