Nucleon tensor charge from exclusiveπ0electroproduction

Abstract

Exclusive o electroproduction from nucleons is suggested for extracting the tensor charge and other quantities related to transversity from experimental data. This process isolates C-parity odd and chiral-odd combinations of t-channel exchange quantum numbers. In a hadronic picture it connects the meson production amplitudes to C-odd Regge exchanges with final state interactions. In a description based on partonic degrees of freedom, the helicity structure for this C-odd process relates to the quark helicity flip, or chiral-odd generalized parton distributions. This differs markedly from deeply virtual Compton scattering, and both vector meson and charged electroproduction, where the axial charge can enter the amplitudes. Contrarily, the tensor charge enters the o process. The connection through the helicity description of the process to both the partonic and hadronic perspectives is studied and exploited in model calculations to indicate how the tensor charge and other transversity parameters can be related to cross section and spin asymmetry measurements over a broad range of kinematics.

On chiral-odd Generalized Parton Distributions

“…We note that our proposal is built on known leading twist factorization theorems, contrarily to other attempts to access transversity GPDs [16]. At large center of mass energy, for chiral-even t−channel exchange, hard exclusive vector meson production beyond leading twist has been consistently described in Ref.…”

Probing Spin Dependent Quark and Gluon Distributions Through Azimuthal and Polarization Asymmetries

“…and analogous terms ( [8,12]), where H T , etc., are the Compton form factors. In the t-channel picture, which has its roots in a Regge analysis of this process [15], one separates the J PC = 1 −− and J PC = 1 +− contributions to the amplitudes for transverse and longitudinal virtual photons, respectively, thus generating two different types of Q 2 dependence at the π 0 vertex [16].…”

“…[12], after showing how DVπ 0 P can be described in terms of chiral-odd GPDs, we estimated all of their contributions to the various observables with particular attention to the ones which were sensitive to the values of the tensor charge. Subsequently, an extension of the Flexible Reggeized Diquark model in the chiral-even sector in Refs.…”

“…We start from the region X ≥ ζ. At fixed M X , the amplitudes read for the Scalar diquark (see [12,13] for the full set of relations):…”

Structure and spin of the nucleon

“…In addition they provide a unique possibility to access "transversity" or chiralodd GPDs through measurements of different azimuthal moments of the cross section. In the handbag approach developed recently by Liuti and Goldstein [10] and Kroll and Goloskokov [11,12] the helicity amplitudes depend on hard partonic subprocess and the GPD and the beam spin asymmetries of exclusive pions combined with other spin and azimuthal asymmetries, which can provide a unique possibility to access the elusive transversity GPDs.…”