arXiv subjects
Publications and source records attributed to S. Wallon.
After recalling the theoretical and experimental status of QCD in the Regge limit and the requirement of high energy scattering process of onium-onium type for testing this limit, we show that the International Linear Collider would be a major step in this field.
The exclusive process e+ e- -> e+ e- rho^0_L rho^0_L allows to study various dynamics and factorization properties of perturbative QCD. At moderate energy, we demonstrate how collinear QCD factorization emerges, involving generalized distribution amplitudes (GDA) and transition distribution amplitudes (TDA). At higher energies, in the Regge limit of QCD, we show that it offers a promising probe of the BFKL resummation effects to be studied at the International Linear Collider (ILC).
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 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 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.
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 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.
We present a theoretical study of exotic hybrid meson (JPC=1-+) production in photon-photon collisions where one of the photons is deeply virtual, including twist 2 and twist 3 contributions. We calculate the cross section of this process which turns out to be large enough to imply sizeable counting rates in the present high luminosity electron-positron colliders. We emphasize theimportance of the pi eta decay channel for the detection of the hybrid meson candidate pi_1(1400) and calculate the cross section and the angular distribution for pi eta pair production in the unpolarized case. This angular distribution is a useful tool for disentangling the hybrid meson signal from the background. Finally, we calculate the single spin asymmetry associated with one initial longitudinally polarized lepton.
We calculate the exclusive process gamma* gamma* ->rho rho at high energy. The Born order estimate and the leading (LLA) and next to leading order (NLLA) BFKL resummation effects show the feasibility of experimental detection in a quite large range of Q2 values at future high energy e+e- linear colliders.
We argue that the electroproduction of exotic particles is a useful tool for study of their partonic structure. In the case of hybrid mesons, the magnitude of their cross sections shows that they are accessible for measurements in existing electroproduction experiments.
Exotic hybrid mesons H, with quantum numbers J^{PC}= 1^{- +} may be copiously produced in the hard exclusive processes gamma^*(Q^2) gamma -> H and gamma^*(Q^2) P(p) -> H P(p') because they have a leading twist distribution amplitude with a sizable coupling constant f_H, which may be estimated through QCD sum rules. The reaction rates scale in the same way as the corresponding rates for usual mesons.
We calculate the cross-section for the diffractive exclusive process gamma*_L (Q_1^2) gamma*_L(Q_2^2) -> rho^0_L rho^0_L, in view of its study in the future high energy e+e- linear collider. The Born order approximation of the amplitude is completely calculable in the hard region Q_1, Q_2 >> Lambda_QCD. The resulting cross-section is large enough for this process to be measurable with foreseen luminosity and energy, for Q_1 and Q_2 in the range of a few GeV.
We present a first estimate of the cross-section for the exclusive process gamma^*_L (Q_1^2) gamma^*_L(Q_2^2) -> rho^0_L rho^0_L, which will be studied in the future high energy e^+ e^- linear collider. As a first step, we calculate the Born order approximation of the amplitude for longitudinally polarized virtual photons and mesons, in the kinematical region s >> -t, Q_1^2, Q_2^2. This process is completely calculable in the hard region Q_1^2, Q_2^2 >> Lambda^2_{QCD}. We perform most of the steps 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 discuss the BLM scale fixing procedure in exclusive electroproduction processes in the Bjorken regime. We show that in the case of vector meson production the usual way to aplly the BLM method fails due to singularities present in equations fixing the BLM scale. We argue that the BLM scale should be extracted from the squared amplitudes which are directly related to observables.
In this paper we deal with high energy scattering in the Regge limit, using a soft cascade approach. We derive an evolution equation for the gluon density in soft gluons cascades in the leading logarithmic approximation of perturbative QCD, and show that this equation reproduces BFKL equation in the forward case. The whole cascade is equivalent to a single gluon whose self-energy is responsible for gluon reggeization. The same type of equation is obtained for the QED case.
The next generation of $e^+e^-$-colliders will offer a possibility of clean testing of QCD dynamics in the Regge limit. Recent progress in the theoretical description of exclusive processes permits for many of them a consistent use of the perturbative QCD methods. We advocate that the exclusive diffractive production of two $ρ$ mesons from virtual photons at very high energies should be measurable at the future linear collider (LC).