I. V. Anikin

QCD factorization of exclusive processes beyond leading twist: gamma*T ---> rho(T) impact factor with twist three accuracy

Abstract We describe a consistent approach to factorization of scattering amplitudes for exclusive processes beyond the leading twist approximation. The method involves the Taylor expansion of the scattering amplitude in the momentum space around the dominant light-cone direction and thus naturally introduces an appropriate set of non-perturbative correlators which encode effects not only of the lowest but also of the higher Fock states of the produced particle. The reduction of original set of correlators to a set of independent ones is achieved with the help of equations of motion and invariance of the scattering amplitude under rotation on the light cone. We compare the proposed method with the covariant method formulated in the coordinate space, based on the operator product expansion. We prove the equivalence of two proposed parametrizations of the ρ T distribution amplitudes. As a concrete application, we compute the expressions of the impact factor for the transition of virtual photon to transversally polarised ρ-meson up to the twist 3 accuracy within these two quite different methods and show that they are identical.

Deep electroproduction of exotic hybrid mesons

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).

On the description of exclusive processes beyond the leading twist approximation

I.V. Anikin, D. Yu. Ivanov, B. Pire, L. Szymanowski, and S. Wallon Bogoliubov Laboratory of Theoretical Physics, JINR, 141980 Dubna, Russia 2 Institute of Mathematics, 630090 Novosibirsk, Russia 3 CPhT, École Polytechnique, CNRS, F-91128 Palaiseau, France 4 So ltan Institute for Nuclear Studies, Hoża 69, 00-681 Warsaw, Poland 5 LPT, Université d’Orsay, CNRS, 91404 Orsay, France UPMC Univ. Paris 6, faculté de physique, 4 place Jussieu, 75252 Paris Cedex 05, France

Exotic hybrid mesons in hard electroproduction

We estimate the sizeable cross section for deep exclusive electroproduction of an exotic J{sup PC}=1{sup -+} hybrid meson in the Bjorken regime. The production amplitude scales like the one for usual meson electroproduction, i.e., as 1/Q{sup 2}. This is due to the nonvanishing 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 {alpha}{sub S} and we explore the consequences of fixing the renormalization scale ambiguity through the Brodsky-Lepage-Mackenzie (BLM) procedure. We study the particular case where the hybrid meson decays through a {pi}{eta} meson pair. We discuss the {pi}{eta} generalized distribution amplitude and then calculate the production amplitude for this process. We propose a forward-backward asymmetry in the production of {pi} and {eta} mesons as a signal for the hybrid meson production. We briefly comment on hybrid electroproduction at very high energy, in the diffractive limit where a QCD Odderon exchange mechanism should dominate. The conclusion of our study is that hard electroproduction is a promising way to study exotic hybrid mesons, in particular, at JLAB, HERA (HERMES), or CERN (Compass)

Search for isotensor exotic meson and twist 4 contribution to gamma* gamma ---> rho rho

We present a theoretical estimate for the cross-section of exclusive

Drell-Yan-like processes and duality

\rho^+\rho^-

gamma* ---> rho(T) impact factor with twist three accuracy

and

Theory and phenomenology of helicity amplitudes for high energy exclusive leptoproduction of the

\rho^0\rho^0

\rho

-meson production in two photon collisions when one of the initial photons is highly virtual. We focus on the discussion of the twist 4 contributions which are related to the production of an exotic isospin 2 resonance of two

-meson

\rho