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Search Results: 1 - 10 of 156874 matches for " B. El-Bennich "
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Planar versus non-planar anti-NN annihilation into mesons in the light of anti-qq operators and the 1/Nc expansion
B. El-Bennich
Physics , 2004, DOI: 10.1103/PhysRevC.72.067001
Abstract: It is argued that in the antiproton-proton annihilation into two mesons $\bar pp\longrightarrow m_1 m_2$, the origin of different restrictive angular momentum selection rules commonly obtained for planar annihilation diagrams $A2$ and for non-planar rearrangement diagrams $R2$ lies in the omission of momentum transfer between an annihilated antiquark-quark pair and a remaining quark or antiquark. If it is included, there is no reason for dismissing one type of diagram in favor of another one. Some considerations in the large $N_c$ limit of QCD equally shed light on the planar and non-planar contributions to the total $\bar NN\to m_1 m_2$ annihilation amplitude.
Relativistic effects and angular dependence in the reaction antiproton-proton -> pi^- pi^+
B. El-Bennich,W. M. Kloet
Physics , 2004, DOI: 10.1103/PhysRevC.70.034002
Abstract: We present a new fit to the LEAR data on antiproton-proton -> pi^- pi^+ differential cross sections and analyzing powers motivated by relativistic considerations. Within a quark model describing this annihilation we argue, since the pions are highly energetic, that relativistic effects cannot be neglected. The intrinsic pion wave functions are Lorentz transformed to the center of mass frame. This change in quark geometry gives rise to additional angular dependence in the transition operators and results in a relative enhancement of higher J \ge 2 partial wave amplitudes. The fit to the data is improved significantly.
A relativistic treatment of pion wave functions in the annihilation antiproton-proton -> pi^-pi^+
B. El-Bennich,W. M. Kloet
Physics , 2004, DOI: 10.1103/PhysRevC.70.034001
Abstract: Quark model intrinsic wave functions of highly energetic pions in the reaction \bar pp->\pi^-\pi^+ are subjected to a relativistic treatment. The annihilation is described in a constituent quark model with A2 and R2 flavor-flux topology and the annihilated quark-antiquark pairs are in 3P_0 and 3S_1 states. We study the effects of pure Lorentz transformations on the antiquark and quark spatial wave functions and their respective spinors in the pion. The modified quark geometry of the pion has considerable impact on the angular dependence of the annihilation mechanisms.
Lorentz contraction, geometry and range in antiproton-proton annihilation into two pions
B. El-Bennich,W. M. Kloet
Physics , 2005, DOI: 10.1063/1.2130132
Abstract: We present a geometric interpretation of the so-called annihilation range in reactions of the type $\bar pp \to$ {\em two light mesons} based upon Lorentz effects in the highly relativistic final states ($\gamma=E_{\mathrm{cm}}/2mc^2\simeq 6.8-8.0$). Lorentz-boosted meson wave functions, within the framework of the constituent quark model, result in a richer angular dependence of the annihilation amplitudes and thus in higher partial wave contributions ($J>1$) than usually obtained. This approach sheds some light on what could be a "{\em short}" annihilation range and how it is influenced by the angular distribution of the final states.
Paris nucleon-antinucleon potential constrained by recent antiprotonic-atom data and antineutron-proton total cross sections
El-Bennich, B.;Lacombe, M.;Loiseau, B.;Wycech, S.
High Energy Physics - Phenomenology , 2008, DOI: 10.1103/PhysRevC.79.054001
Abstract: We report on an updated Paris nucleon-antinucleon optical potential. The long- and intermediate-range real parts are obtained by G-parity transformation of the Paris nucleon-nucleon potential based on a theoretical dispersion-relation treatment of the correlated and uncorrelated two-pion exchange. The short-range imaginary potential parametrization results from the calculation of the nucleon-antinucleon annihilation box diagram into two mesons with a nucleon-antinucleon intermediate state in the crossed channel. The parametrized real and imaginary short range parts are determined by fitting not only the existing experimental data included in the 1999 version of the Paris nucleon-antinucleon potential, but also the recent antiprotonic-hydrogen data and antineutron-proton total cross sections. The description of these new observables is improved. Only this readjusted potential generates an isospin zero 1S0, 52 MeV broad quasibound state at 4.8 MeV below the threshold. Recent BES data on J/psi decays could support the existence of such a state.
Paris nucleon-antinucleon potential constrained by recent antiprotonic-atom data and antineutron-proton total cross sections
B. El-Bennich,M. Lacombe,B. Loiseau,S. Wycech
Physics , 2008, DOI: 10.1103/PhysRevC.79.054001
Abstract: We report on an updated Paris nucleon-antinucleon optical potential. The long- and intermediate-range real parts are obtained by G-parity transformation of the Paris nucleon-nucleon potential based on a theoretical dispersion-relation treatment of the correlated and uncorrelated two-pion exchange. The short-range imaginary potential parametrization results from the calculation of the nucleon-antinucleon annihilation box diagram into two mesons with a nucleon-antinucleon intermediate state in the crossed channel. The parametrized real and imaginary short range parts are determined by fitting not only the existing experimental data included in the 1999 version of the Paris nucleon-antinucleon potential, but also the recent antiprotonic-hydrogen data and antineutron-proton total cross sections. The description of these new observables is improved. Only this readjusted potential generates an isospin zero 1S0, 52 MeV broad quasibound state at 4.8 MeV below the threshold. Recent BES data on J/psi decays could support the existence of such a state.
The reaction antirproton-proton into pi+pi-: relativistic aspects and final-state interaction in the pion wave functions
Bruno El-Bennich,W. M. Kloet,B. Loiseau
Physics , 2003,
Abstract: We use a distorted wave approximation approach which includes $^3P_0$ and $^3S_1$ quark-antiquark annihilation mechanisms to reproduce the data set from LEAR on $\bar p p\to \pi^+\pi^-$ in the range from 360 to 1550 MeV/c. Improvements of the model are sought by implementing final-state interactions of the pions and by observing that the annihilation is too short-ranged in earlier attempts to describe the data. While the former improvement is due to to the final-state $\pi\pi$ wave functions solely, the latter one originates from quark wave functions for proton, antiproton, and pions with radii slightly larger than the respective measured charge radii. This increase in hadron radius, as compared with typically much smaller radii used before in the quark model, increases the annihilation range and thereby the amplitudes for $J\ge2$ are much higher. Finally, given the very high kinetic energy of the final pions, we investigate the role of relativistic corrections in the pion wave functions when boosted into the center-of-mass frame.
Annihilation range and final-state interaction in the antiproton-proton annihilation into pi-pi+
Bruno El-Bennich,W. M Kloet,B. Loiseau
Physics , 2003, DOI: 10.1103/PhysRevC.68.014003
Abstract: The large set of accurate data on differential cross section and analyzing power from the CERN LEAR experiment on $\bar pp \to \pi^+\pi^-$ in the range from 360 to 1550 MeV/c is well reproduced within a distorted wave approximation approach. The initial $\bar pp$ scattering wave functions originate from a recent $\bar N N$ model. The transition operator is obtained from a combination of the $^3P_0$ and $^3S_1$ quark-antiquark annihilation mechanisms. A good fit to the data, in particular the reproduction of the double dip structure observed in the analyzing powers, requires quark wave functions for proton, antiproton, and pions with radii slightly larger than the respective measured charge radii. This corresponds to an increase in range of the annihilation mechanisms and consequently the amplitudes for total angular momentum J=2 and higher are much larger than in previous approaches. The final state $\pi\pi$ wave functions, parameterized in terms of $\pi\pi$ phase shifts and inelasticities, are also a very important ingredient for the fine tuning of the fit to the observables.
Flavourful hadronic physics
B. El-Bennich,M. A. Ivanov,C. D. Roberts
Physics , 2009, DOI: 10.1016/j.nuclphysbps.2010.02.026
Abstract: We review theoretical approaches to form factors that arise in heavy-meson decays and are hadronic expressions of non-perturbative QCD. After motivating their origin in QCD factorisation, we retrace their evolution from quark-model calculations to non-perturbative QCD techniques with an emphasis on formulations of truncated heavy-light amplitudes based upon Dyson-Schwinger equations. We compare model predictions exemplarily for the B\to\pi transition form factor and discuss new results for the g_{D*D\pi} coupling in the hadronic D* decay.
Mesonic interactions and their contribution to strong phases in flavor physics
El-Bennich, B.;Furman, A.;Kaminski, R.;Lesniak, L.;Loiseau, B.;Moussallam, B.
High Energy Physics - Phenomenology , 2007,
Abstract: We analyze the contributions of hadronic final-state interactions to the strong phases generated in the B -> Kpipi weak decays. To this end, we develop an alternative approach to the commonly employed isobar model based upon scalar and vector form factors for pion-pion and pion-kaon interactions.
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