-Nous discutons le rôle des processus inélastiques pour l'interpretation des dibaryons observés d... more -Nous discutons le rôle des processus inélastiques pour l'interpretation des dibaryons observés dans les déphasages NN et nous soulignons fortement le besoin d'une bonne compréhension de ces réactions.
We analyze the large recoil behaviour of heavy meson transition form factors using the Brodsky-Le... more We analyze the large recoil behaviour of heavy meson transition form factors using the Brodsky-Lepage hard scattering formalism. At the leading order of the heavy mass scale the large recoil form factors exhibit a new type of heavy quark symmetry. We discuss next-to-leading mass effects and present explicit 1/MQ expressions for the form factors in the peaking approximation.
We investigate the reaction π − p → D − Λ + c within the generalized parton picture. The process ... more We investigate the reaction π − p → D − Λ + c within the generalized parton picture. The process is described by a handbag-type mechanism with the charm-quark mass acting as the hard scale. As in the case of preceding work onp p →Λ − c Λ + c we argue that the process amplitude factorizes into one for the perturbatively calculable partonic subprocessū u →c c and hadronic matrix elements that can be parameterized in terms of generalized parton distributions. Modeling the generalized parton distributions by overlaps of (valence-quark) light-cone wave functions for the hadrons involved, we obtain numerical results for unpolarized differential and integrated cross sections as well as spin observables. Our approach works well above the production threshold (s 20 GeV 2) in the forward hemisphere and predicts unpolarized cross sections of the order of nb, a finding that could be of interest in view of plans to measure π − p → D − Λ + c at J-PARC.
Exclusive Processes at High Momentum Transfer, Jul 9, 2002
The basic theoretical ideas of the handbag factorization and its application to wideangle scatter... more The basic theoretical ideas of the handbag factorization and its application to wideangle scattering reactions are reviewed. With regard to the present experimental program carried out at JLab, wide-angle Compton scattering is discussed in some detail.
The b-u skewed parton distributions (SPDs) are discussed. The SPDs allow an unambigous superposit... more The b-u skewed parton distributions (SPDs) are discussed. The SPDs allow an unambigous superposition of overlap and resonsance contributions and their zeroth order moments represent the B → π transition form factors. The values of the form factors at maximum recoil are found to be F + (0) = F 0 (0) = 0.22 ± 0.05 in agreement with measurements of the B → ππ branching ratio. The branching ratios for the semi-leptonic B → π decays are evaluated too.
We reanalyze the ηγ and η γ transition form factors within the modified hard scattering approach ... more We reanalyze the ηγ and η γ transition form factors within the modified hard scattering approach on the basis of new experimental data from CLEO [1] and L3 [2]. Our approach perfectly describes the experimental data over a wide range of the virtuality of the probing photon, 1 GeV 2 ≤ Q 2 ≤ 15 GeV 2. The analysis provides hints that the conventional flavor octet-singlet scheme for the η-η mixing is too simple. A more general mixing scheme on the other hand, involving two mixing angles, leads to a very good description of the transition form factors and also accounts for the two-photon decay widths of the η and η mesons as well as for the ratio of the widths for the J/ψ → η γ and J/ψ → ηγ decays. We also investigate the questions of possible deviations of the η and η distribution amplitudes from the asymptotic form and of eventual intrinsic charm in the η and η mesons. We estimate the charm decay constant of the η meson to lie within the range −65 MeV ≤ f c η ≤ 15 MeV.
We investigate the soft handbag contribution to two-photon annihilation into pion or kaon pairs a... more We investigate the soft handbag contribution to two-photon annihilation into pion or kaon pairs at large energy and momentum transfer. The amplitude is expressed as a hard γγ → q¯q subprocess times a form factor describing the soft transition from q¯q to the meson pair. We find the calculated angular dependence of the cross section in good agreement with data, and extract annihilation form factors of plausible size. A key prediction of the handbag mechanism is that the differential cross section is the same for charged and neutral pion pairs, in striking contrast with what is found in the hard scattering approach. 1
The process p¯p → Λ + c ¯ Λ − c is investigated within the handbag approach. It is shown that the... more The process p¯p → Λ + c ¯ Λ − c is investigated within the handbag approach. It is shown that the dominant dynamical mechanism, characterized by the partonic subprocess uū → c¯c, factorizes in the sense that only the subprocess contains highly virtual partons, a gluon to lowest order of perturbative QCD, while the hadronic matrix elements embody only soft scales and can be parameterized in terms of helicity flip and non-flip generalized parton distributions. Modelling these parton distributions by overlaps of light-cone wave functions for the involved baryons we are able to predict cross sections and spin correlation parameters for the process of interest. 1
Physics at LEAR with Low-Energy Cooled Antiprotons
The present status of forward dispersion relations for pp scattering is investigated. It is stres... more The present status of forward dispersion relations for pp scattering is investigated. It is stressed that at low energies the situation is not yet settled, precise total cross-section and Coulomb-interference data are required for in particular at very low energies (pL < 0.3 GeV/c). Furthermore, possible applications of non-forward dispersion relations are discussed.
The role of generalized parton distributions in wide-angle exclusive reactions will be discussed.... more The role of generalized parton distributions in wide-angle exclusive reactions will be discussed. In contrast to deep virtual exclusive reactions the wide angle processes offer the possibility of investigating the generalized parton distributions at large momentum transfer.
Proceedings of LIGHT CONE 2008 Relativistic Nuclear and Particle Physics — PoS(LC2008)
We study proton-antiproton annihilation into Λ cΛc pairs within the generalized parton picture. O... more We study proton-antiproton annihilation into Λ cΛc pairs within the generalized parton picture. Our starting point is the double handbag diagram which is shown to factorize into soft generalized parton distributions for the p → Λ c (andp →Λ c) transition and a hard subprocess amplitude for uū → cc. Thereby the mass of the charm quark is taken as the hard scale so that our results are not restricted to large scattering angles and/or incredibly large energies. Modelling the generalized parton distributions for the p → Λ c transition by an overlap of simple quark-diquark light-cone wave functions we make first predictions for p → Λ c transition form factors and unpolarized pp → Λ cΛc cross sections. Our findings may become interesting in view of forthcoming experiments at FAIR in Darmstadt.
It is reported on an analysis of vector meson electroproduction at small Bjorken-x (x Bj) within ... more It is reported on an analysis of vector meson electroproduction at small Bjorken-x (x Bj) within the handbag approach. Using a model for the generalized parton distributions (GPDs) and calculating the partonic subprocess, electroproduction off gluons, within the modified perturbative approach, cross sections and spin density matrix elements (SDME) are evaluated. The numerical results of this analysis agree fairly well with recent HERA data. Contribution to DIS05, Madison (USA)
-Nous discutons le rôle des processus inélastiques pour l'interpretation des dibaryons observés d... more -Nous discutons le rôle des processus inélastiques pour l'interpretation des dibaryons observés dans les déphasages NN et nous soulignons fortement le besoin d'une bonne compréhension de ces réactions.
We analyze the large recoil behaviour of heavy meson transition form factors using the Brodsky-Le... more We analyze the large recoil behaviour of heavy meson transition form factors using the Brodsky-Lepage hard scattering formalism. At the leading order of the heavy mass scale the large recoil form factors exhibit a new type of heavy quark symmetry. We discuss next-to-leading mass effects and present explicit 1/MQ expressions for the form factors in the peaking approximation.
We investigate the reaction π − p → D − Λ + c within the generalized parton picture. The process ... more We investigate the reaction π − p → D − Λ + c within the generalized parton picture. The process is described by a handbag-type mechanism with the charm-quark mass acting as the hard scale. As in the case of preceding work onp p →Λ − c Λ + c we argue that the process amplitude factorizes into one for the perturbatively calculable partonic subprocessū u →c c and hadronic matrix elements that can be parameterized in terms of generalized parton distributions. Modeling the generalized parton distributions by overlaps of (valence-quark) light-cone wave functions for the hadrons involved, we obtain numerical results for unpolarized differential and integrated cross sections as well as spin observables. Our approach works well above the production threshold (s 20 GeV 2) in the forward hemisphere and predicts unpolarized cross sections of the order of nb, a finding that could be of interest in view of plans to measure π − p → D − Λ + c at J-PARC.
Exclusive Processes at High Momentum Transfer, Jul 9, 2002
The basic theoretical ideas of the handbag factorization and its application to wideangle scatter... more The basic theoretical ideas of the handbag factorization and its application to wideangle scattering reactions are reviewed. With regard to the present experimental program carried out at JLab, wide-angle Compton scattering is discussed in some detail.
The b-u skewed parton distributions (SPDs) are discussed. The SPDs allow an unambigous superposit... more The b-u skewed parton distributions (SPDs) are discussed. The SPDs allow an unambigous superposition of overlap and resonsance contributions and their zeroth order moments represent the B → π transition form factors. The values of the form factors at maximum recoil are found to be F + (0) = F 0 (0) = 0.22 ± 0.05 in agreement with measurements of the B → ππ branching ratio. The branching ratios for the semi-leptonic B → π decays are evaluated too.
We reanalyze the ηγ and η γ transition form factors within the modified hard scattering approach ... more We reanalyze the ηγ and η γ transition form factors within the modified hard scattering approach on the basis of new experimental data from CLEO [1] and L3 [2]. Our approach perfectly describes the experimental data over a wide range of the virtuality of the probing photon, 1 GeV 2 ≤ Q 2 ≤ 15 GeV 2. The analysis provides hints that the conventional flavor octet-singlet scheme for the η-η mixing is too simple. A more general mixing scheme on the other hand, involving two mixing angles, leads to a very good description of the transition form factors and also accounts for the two-photon decay widths of the η and η mesons as well as for the ratio of the widths for the J/ψ → η γ and J/ψ → ηγ decays. We also investigate the questions of possible deviations of the η and η distribution amplitudes from the asymptotic form and of eventual intrinsic charm in the η and η mesons. We estimate the charm decay constant of the η meson to lie within the range −65 MeV ≤ f c η ≤ 15 MeV.
We investigate the soft handbag contribution to two-photon annihilation into pion or kaon pairs a... more We investigate the soft handbag contribution to two-photon annihilation into pion or kaon pairs at large energy and momentum transfer. The amplitude is expressed as a hard γγ → q¯q subprocess times a form factor describing the soft transition from q¯q to the meson pair. We find the calculated angular dependence of the cross section in good agreement with data, and extract annihilation form factors of plausible size. A key prediction of the handbag mechanism is that the differential cross section is the same for charged and neutral pion pairs, in striking contrast with what is found in the hard scattering approach. 1
The process p¯p → Λ + c ¯ Λ − c is investigated within the handbag approach. It is shown that the... more The process p¯p → Λ + c ¯ Λ − c is investigated within the handbag approach. It is shown that the dominant dynamical mechanism, characterized by the partonic subprocess uū → c¯c, factorizes in the sense that only the subprocess contains highly virtual partons, a gluon to lowest order of perturbative QCD, while the hadronic matrix elements embody only soft scales and can be parameterized in terms of helicity flip and non-flip generalized parton distributions. Modelling these parton distributions by overlaps of light-cone wave functions for the involved baryons we are able to predict cross sections and spin correlation parameters for the process of interest. 1
Physics at LEAR with Low-Energy Cooled Antiprotons
The present status of forward dispersion relations for pp scattering is investigated. It is stres... more The present status of forward dispersion relations for pp scattering is investigated. It is stressed that at low energies the situation is not yet settled, precise total cross-section and Coulomb-interference data are required for in particular at very low energies (pL < 0.3 GeV/c). Furthermore, possible applications of non-forward dispersion relations are discussed.
The role of generalized parton distributions in wide-angle exclusive reactions will be discussed.... more The role of generalized parton distributions in wide-angle exclusive reactions will be discussed. In contrast to deep virtual exclusive reactions the wide angle processes offer the possibility of investigating the generalized parton distributions at large momentum transfer.
Proceedings of LIGHT CONE 2008 Relativistic Nuclear and Particle Physics — PoS(LC2008)
We study proton-antiproton annihilation into Λ cΛc pairs within the generalized parton picture. O... more We study proton-antiproton annihilation into Λ cΛc pairs within the generalized parton picture. Our starting point is the double handbag diagram which is shown to factorize into soft generalized parton distributions for the p → Λ c (andp →Λ c) transition and a hard subprocess amplitude for uū → cc. Thereby the mass of the charm quark is taken as the hard scale so that our results are not restricted to large scattering angles and/or incredibly large energies. Modelling the generalized parton distributions for the p → Λ c transition by an overlap of simple quark-diquark light-cone wave functions we make first predictions for p → Λ c transition form factors and unpolarized pp → Λ cΛc cross sections. Our findings may become interesting in view of forthcoming experiments at FAIR in Darmstadt.
It is reported on an analysis of vector meson electroproduction at small Bjorken-x (x Bj) within ... more It is reported on an analysis of vector meson electroproduction at small Bjorken-x (x Bj) within the handbag approach. Using a model for the generalized parton distributions (GPDs) and calculating the partonic subprocess, electroproduction off gluons, within the modified perturbative approach, cross sections and spin density matrix elements (SDME) are evaluated. The numerical results of this analysis agree fairly well with recent HERA data. Contribution to DIS05, Madison (USA)
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