O.V. Teryaev

PROBING PARTONIC STRUCTURE IN GAMMA GAMMA PI PI NEAR THRESHOLD

Hadron pair production gamma* gamma -> h hbar in the region where the c.m. energy is much smaller than the photon virtuality can be described in a factorized form, as the convolution of a partonic handbag diagram and generalized distribution amplitudes which are new non-perturbative functions describing the exclusive fragmentation of a quark-antiquark pair into two hadrons. Scaling behavior and a selection rule on photon helicity are signatures of this mechanism. The case where h is a pion is emphasized.

Towards a Solution of the Charmonium Production Controversy: k ⊥ Factorization versus Color-Octet Mechanism

The cross section of chi_{cJ} hadroproduction is calculated in the k_t-factorization approach. We find a significant contribution of the chi_{c1} state due to non-applicability of the Landau-Yang theorem because of off-shell gluons. The results are in agreement with data and, in contrast to the collinear factorization, show a dominance of the color singlet part and a strong suppression of the color octet contribution. Our results could therefore lead to a solution of the longstanding controversy between the color singlet model and the color octet mechanism.

Probing chiral-odd GPDs in diffractive electroproduction of two vector mesons

Abstract We consider the electroproduction of two vector mesons with a large rapidity gap between them on a nucleon target in the process γ ∗ N→ρ 1 ρ 2 N′ . We calculate the Born term for this process within the collinear factorization framework. Thexa0resulting scattering amplitude may be represented as a convolution of an impact factor describing the γ ∗ →ρ 1 transition and an amplitude describing the N → 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.

Towards a Solution of the Charmonium Production Controversy: k[perpendicular] Factorization versus Color-Octet Mechanism

The cross section of chi(cJ) hadroproduction is calculated in the k( perpendicular)-factorization approach. We find a significant contribution of the chi(c1) state due to non-applicability of the Landau-Yang theorem because of off-shell gluons. The results are in agreement with data and, in contrast to the collinear factorization, show a dominance of the color-singlet part and a strong suppression of the color octet contribution. Our results could therefore lead to a solution of the long-standing controversy between the color-singlet model and the color-octet mechanism.

Direct

The hadroproduction of direct

J/\psi

J/ensuremath{psi}

hadroproduction in

in the framework of the

k^-

{k}_{ensuremath{perp}}

perpendicular factorization and the color octet mechanism

-factorization approach is studied. The color-singlet contribution is essentially larger than in the collinear approach but is still an order of magnitude below the data. The deficit may be well described by the color octet contribution with the value of the matrix element

Pomeron - odderon interference effects in electroproduction of two pions

〈0|{O}_{8}^{J/ensuremath{psi}}{(}^{3}{S}_{1})|0〉