arXiv subjects
Publications and source records attributed to L. Szymanowski.
We calculate the Born order cross-section for the exclusive production of rho meson pairs in e+e- scattering in the Regge limit of QCD and we show the feasibility of the measurement of this process at the ILC. We also investigate the leading and next-to-leading order BFKL evolution, making this process a very clean test of the BFKL resummation effects.
We give a brief overview of the theoretical status of the Transition Distribution Amplitudes and discuss their experimental near future.
Electroproduction of two mesons well separated in rapidity allows the first feasible selective access to chiral-odd transversity GPDs provided one of these mesons is a transversely polarized vector meson rho_T.
Virtual photons have proven to be very efficient probes of the hadronic structure, mostly through deep inelastic scattering and related processes. The advent of high luminosity lepton beams has allowed to enlarge the studied processes to hard exclusive reactions, such as deeply virtual Compton scattering and the electroproduction of mesons. We discuss theoretical progress which has lately been quite remarkable in this domain and first much encouraging experimental data.
We calculate the leading order BFKL amplitude for the exclusive diffractive process γ*_L(Q1^2) γ*_L(Q2^2) \to ρ_L^0 ρ_L^0 in the forward direction, which can be studied in future high energy e^+e^- linear colliders. The resummation effects are very large compared to the fixed-order calculation. We also estimate the next-to-leading logarithmic corrections to the amplitude by using a specific resummation of higher order effects and find a substantial growth with energy, but smaller than in the leading logarithmic approximation.
We present an estimate of the cross-section for the exclusive production of a rho_L^0-meson pair in e^+e^- scattering, which will be studied in the future high energy International Linear Collider. For this aim, we complete calculations of the Born order approximation of the amplitudes gamma^*_{L,T}(Q_1^2) gamma^*_{L,T}(Q_2^2) -> rho_L^0 rho_L^0, for arbitrary polarization of virtual photons and longitudinally polarized mesons, in the kinematical region s >> -t, Q_1^2, Q_2^2. These processes are completely calculable in the hard region Q_1^2, Q_2^2 >> Lambda^2_{QCD} and we perform most of the calculations in an analytical way. The resulting cross-section turns out to be large enough for this process to be measurable with foreseen luminosity and energy, for Q_1^2 and Q_2^2 in the range of a few GeV^2.
We study pp and p\bar p collisions which lead to the exclusive production of J/psi or Upsilon from the pomeron-odderon and the pomeron-photon fusion. We calculate scattering amplitudes of these processes in the lowest order approximation and in the framework of k_T factorization. We present estimates of cross sections for the kinematic conditions of the Tevatron and of the LHC.
We study the scaling regime of nucleon - anti-nucleon annihilation into a deeply virtual photon and a meson, bar p N -> gamma* pi. We obtain the leading twist amplitude in the kinematical region where it factorizes into an antiproton distribution amplitude, a short-distance matrix element related to nucleon form factor and the long-distance dominated transition distribution amplitudes which describe the nucleon to meson transition. We give the Q^2 evolution equation for these transition distribution amplitudes. The scaling of the cross section of this process may be tested at the proposed GSI intense anti-proton beam facility FAIR with the PANDA or PAX detectors. We comment on related processes such as pi N -> N' gamma* and gamma* N -> N' pi which may be experimentally studied at intense meson beams facilities and at JLab or Hermes, respectively.
We consider deeply virtual Compton scattering on a photon target, in the generalized Bjorken limit, at the Born order and in the leading logarithmic approximation. We interpret the result as a factorized amplitude of a hard process described by handbag diagrams and anomalous generalized parton distributions in the photon. This anomalous part, with its characteristic ln Q2 dependence, is present both in the DGLAP and in the ERBL regions. As a consequence, these generalized parton distributions of the photon obey DGLAP-ERBL evolution equations with an inhomogeneous term.
We have shown that the lowest order QCD amplitude, i.e. the quark exchange contribution, to the forward production of a pair of longitudinally polarized rmesons in the scattering of two virtual photons gamma (Q1) gamma (Q2) rho rho factorizes in two different ways: the part with transverse photons is described by the QCD factorization formula involving the generalized distribution amplitude of two final rho mesons, whereas the part with longitudinally polarized photons takes the QCD factorized form with the gamma rho transition distribution amplitude. Perturbative expressions forthese, in general, non-perturbative functions are obtained in terms of the rho meson distribution amplitude.
We use general relations between the Transition Distribution Amplitudes (TDAs), entering the description of the p -> pi0 transition, and the proton Distribution Amplitudes (DAs) in the soft-pion limit to estimate the size of the amplitude for backward electroproduction of pi0 at large Q2.
The QCD analysis of the recent experimental data (L3@LEP) of the hard exclusive $ρρ$ production in two photon collisions shows that these data can be understood as a signal for the existence of an exotic isotensor resonance with a mass around $1.5 {\rm GeV}$. We also argue that hard exclusive reactions are a powerful tool for an experimental study of exotic hybrid mesons with $J^{PC}=1^{-+}$.
We estimate the sizeable cross section for deep exclusive electroproduction of an exotic $J^{PC}=1^{-+}$ hybrid meson in the Bjorken regime. The production amplitude scales like the one for usual meson electroproduction, {\it i.e.} as $1/Q^2$. This is due to the non-vanishing leading twist distribution amplitude for the hybrid meson, which may be normalized thanks to its relation to the energy momentum tensor and to the QCD sum rules technique. The hard amplitude is considered up to next--to--leading order in $α_{S}$ and we explore the consequences of fixing the renormalization scale ambiguity through the BLM procedure.
We analyse deeply-virtual Compton scattering on a proton target, gamma* P -> P' gamma in the backward region and in the scaling regime. We define the transition distribution amplitudes which describe the proton to photon transition. Model-independent predictions are given to test this description, for current or planned experiments at JLab or by Hermes.
The generalized Bjorken regime of exclusive reactions opens new ways to explore the hadron structure. We shortly review the present status of this domain where generalized parton distributions, generalized distribution amplitudes and transition distribution amplitudes describe various aspects of confinement physics.
We calculate the lowest order QCD amplitude, i.e. the quark exchange contribution, to the forward production amplitude of a pair of longitudinally polarized $ρ$ mesons in the scattering of two virtual photons $γ^*(Q_1) γ^*(Q_2) \to ρ^0_L ρ^0_L$. We show that the scattering amplitude simultaneously factorizes in two quite different ways: the part with transverse photons is described by the QCD factorization formula involving the generalized distribution amplitude of two final $ρ$ mesons, whereas the part with longitudinally polarized photons takes the QCD factorized form with the $γ^*_L \to ρ^0_L$ transition distribution amplitude. Perturbative expressions for these, in general, non-perturbative functions are obtained in terms of the $ρ-$meson distribution amplitude.
The chiral-odd generalized parton distribution (GPD), or transversity GPD, of the nucleon can be accessed experimentally through the photo- or electroproduction of two vector mesons on a polarized nucleon target, γ^(*) N --> ρ_1 ρ_2 N', where ρ_1 is produced at large transverse momentum, ρ_2 is transversely polarized, and the mesons are separated by a large rapidity gap. We predict the cross section for this process for both transverse and longitudinal ρ_{2} production. To this end we propose a model for the transversity GPD H_T(x,ξ,t), and give an estimate of the relative sizes of the transverse and longitudinal ρ_{2} cross sections. We show that a dedicated experiment at high energy should be able to measure the transversity content of the proton.
We study the exclusive production of pi pi and rho pi in hard gamma* gamma scattering in the forward kinematical region where the virtuality of one photon provides us with a hard scale in the process. The newly introduced concept of Transition Distribution Amplitudes (TDA) is used to perform a QCD calculation of these reactions thanks to two simple models for TDAs. Cross sections for rho pi and pi pi production are evaluated and compared to the possible background from the Bremsstrahlung process. This picture may be tested at intense electron-positron colliders such as CLEO and B factories. The cross section e gamma -> e' pi0 pi0 is finally shown to provide a possible determination of the pi0 axial form factor, FA, at small t, which seems not to be measurable elsewhere.