arXiv subjects
Publications and source records attributed to L. Szymanowski.
Exclusive electroproduction of a K or K^* meson on the nucleon can give a Theta^+ pentaquark in the final state. This reaction offers an opportunity to investigate the structure of pentaquark baryons at parton level. We discuss the generalized parton distributions for the N -> Theta^+ transition and give the leading order amplitude for electroproduction in the Bjorken regime.
We evaluate the leading order amplitude for the deep exclusive electroproduction of an exotic hybrid meson in the Bjorken regime. We show that, contrary to naive expectation, this amplitude factorizes at the twist 2 level and thus scales like usual meson electroproduction when the virtual photon and the hybrid meson are longitidinally polarized. Exotic hybrid mesons may thus be studied in electroproduction experiments at JLAB, HERA (HERMES) or CERN (COMPASS).
The process of a light neutral vector meson electroproduction is studied in the framework of QCD factorization in which the amplitude factorizes in a convolution of the nonperturbative meson distribution amplitude and the generalized parton densities with the perturbatively calculable hard-scattering amplitudes. We derive a complete set of hard-scattering amplitudes at next-to-leading order (NLO) for the production of vector mesons, $V=ρ^0, ω, ϕ$.
Electroproduction of two vector mesons with a large rapidity gap between them provides the first feasible selective access to chiral-odd GPDs. The scattering amplitude of the process $ γ^* N \to ρ_L^0 ρ_T^+ N'$ may be represented as a convolution of an impact factor describing the $γ^* \to ρ_L^0$ transition and an amplitude describing the $N\to ρ_T^+ N'$ transition, analogously to deeply exclusive electroproduction of a meson, the virtual photon being replaced by a Pomeron. The production of a transversely polarized vector meson $ρ_T^+$ selects a chiral-odd GPD in the proton.
Exclusive electroproduction of a K or K* meson on the nucleon can give a Theta+ pentaquark in the final state. This reaction offers an opportunity to investigate the structure of pentaquark baryons at parton level. We discuss the generalized parton distributions for the N-->Theta+ transition and give the leading order amplitude for electroproduction in the Bjorken regime. Different production channels contain complementary information about the distribution of partons in a pentaquark compared with their distribution in the nucleon. Measurement of these processes may thus provide deeper insight into the very nature of pentaquarks.
We study Pomeron-Odderon interference effects giving rise to charge and single-spin asymmetries in diffractive electroproduction of a $π^+ π^-$ pair. The final state interactions and the role of $f_0$ meson are discussed. The absence of $f_0$ signal in the charge asymmetry observed by HERMES may be due to the smalness of its quark component.
We investigate the quantum-mechanical interpretation of models with non-Hermitian Hamiltonians and real spectra. After describing a general framework to reformulate such models in terms of Hermitian Hamiltonians defined on the Hilbert space $L_2(-\infty,\infty)$, we discuss the significance of the algebra of physical observables.
We consider the process gamma^* N -> M_1 M_2 N' with a large rapidity gap between the two mesons M_1 and M_2. Within the QCD collinear approximation, the scattering amplitude may be written as a convolution of an impact factor describing the gamma^* -> M_1 transition and an amplitude describing the N -> M_2 N' collinear process.
We develop an impact representation for the generalized distribution amplitude which describes the exclusive hadronization of a quark-antiquark pair to a pair of mesons. Experiments such as gamma^* gamma -> pi pi and gamma^* N -> pi pi N' are shown to probe the transverse size of the hadronization region of the quark antiquark pair that one can interpret as the transverse overlap of the two emerging mesons. An astonishing feature of this description is that low energy pi pi phase shift analysis can be used for understanding some properties of quark hadronization process.
We consider the electroproduction of two vector mesons with a large rapidity gap between them on a nucleon target in the process $ γ^* N \to ρ_1 ρ_2 N'$. We calculate the Born term for this process within the collinear factorization framework. The resulting scattering amplitude may be represented as a convolution of an impact factor describing the $γ^* \to ρ_1$ transition and an amplitude describing the $N\to ρ_2 N'$ transition. The latter amplitude is analogous to deeply virtual electroproduction of a meson, the virtual photon being replaced by two gluon (Pomeron) exchange . The long distance part of this amplitude is described by Generalized Parton Distributions (GPD) and meson light-cone distributions. The selection of a transversely polarized vector meson $ρ_2$ provides the first feasible selective access to chiral-odd GPD.
We study Pomeron-Odderon interference effects giving rise to charge and single-spin asymmetries in diffractive electroproduction of a $π^+ π^-$ pair. We calculate these asymmetries in the Born approximation of QCD in a kinematical domain accessible to HERA experiments.
We review the results of our studies on the charge and the spin asymmetries in the electroproduction of $π^+ π^-$ which are the observables sensitive to the Pomeron-Odderon interference.
We study Pomeron-Odderon interference effects giving rise to charge and single-spin asymmetries in diffractive electroproduction of a pi+ pi- pair. We calculate these asymmetries originating from both longitudinal and transverse polarizations of the virtual photon in the framework of QCD and in the Born approximation, in a kinematical domain accessible to HERA experiments. We predict a sizable charge asymmetry with a characteristic dependence on the invariant mass of the pi+ pi- pair, which makes this observable very important for establishing the magnitude of the Odderon exchange in hard processes. The single spin asymmetry turns out to be rather small. We briefly discuss future improvements of our calculations and their possible effects on the results.
The interference of Pomeron and Odderon amplitudes gives rise to a charge asymmetry in the diffractive electroproduction of a pi+pi- -pair. We calculate this charge asymmetry in perturbative QCD in the Born approximation and on the leading Q^2-level. The numerical evaluation shows a sizeable asymmetry in an experimentally accessible kinematical region. We find a characteristic m_{pi+pi} -dependence mainly dictated by the relevant Breit-Wigner-amplitudes and the corresponding phase-shifts.
We argue that coherent production of hard dijets by linearly polarized real photons can provide direct evidence for chirality violation in hard processes, the first measurement of the magnetic susceptibility of the quark condensate and the photon distribution amplitude. It can also serve as a sensitive probe of the generalized gluon parton distribution. Numerical calculations are presented for HERA kinematics.
Charge asymmetries in diffractive electroproduction of two mesons are proportional to the interference of Pomeron and Odderon exchange amplitudes. We calculate in the framework of QCD and in the Born approximation a forward-backward charge asymmetry which turns out to be sizable in a kinematical domain accessible to HERA experiments. We predict a distinctive dependence of this asymmetry on the invariant mass of the two pions. Testing this prediction is a crucial step in the discovery of the QCD-Odderon.
We carry out a detailed calculation of the cross section of pion diffraction dissociation into two jets with large transverse momenta, originating from a hard gluon exchange between the pion constituents. Both the quark and the gluon contribution are considered and in the latter case we present calculations both in covariant and in axial gauges. We find that the standard collinear factorization does not hold in this reaction. The structure of non-factorizable contributions is discussed and the results are compared with the experimental data. Our conclusion is that the existing theoretical uncertainties do not allow, for the time being, for a quantitative extraction of the pion distribution amplitude.
We present main ideas and obtained results of our recent calculations of Coulomb and QCD contribution to the pion diffractive dissociation into two jets.