6,166 research outputs found

    Charm Meson Spectroscopy at Babar and CLEO-C

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    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

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    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

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    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

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    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

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    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

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    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

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    An eikonal expansion is used to provide systematic corrections to the eikonal approximation through order 1/k21/k^2, where kk 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

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    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

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    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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