Abstract
Exclusive electroproduction of vector mesons has been measured on hydrogen and deuterium targets at HERMES using the 27.6 GeV electron/positron beam of HERA. From this process, more information can be obtained about generalized parton distributions (GPDs), which provide a unified description of the structure of hadrons embedding longitudinal-momentum distributions (ordinary PDFs) and transverse-position information (form factors). The study of the azimuthal distribution of the decay products via spin-density matrix elements provide constraints on helicity-amplitudes used to describe exclusive vector-meson production. Recent results from the HERMES experiment on the production of rho, omega and phi mesons will be presented.
Highlights
The structure of nucleon, in the view of recent theoretical developments, is more comprehensively described by the generalized parton distribution (GPDs) functions [1,2,3]
More information can be obtained about generalized parton distributions (GPDs), which provide a unified description of the structure of hadrons embedding longitudinal-momentum distributions and transverse-position information
In contrast to form factors and parton distribution functions, which are one dimensional distributions, the GPDs contain a correlated information on transverse spatial and longitudinal momentum distributions of partons [4, 5], the elastic form factors and parton distributions appear as moments and limiting cases of GPDs, respectively
Summary
The structure of nucleon, in the view of recent theoretical developments, is more comprehensively described by the generalized parton distribution (GPDs) functions [1,2,3]. The GPDs can be accessed through measurements of hard exclusive lepton-nucleon scattering processes. The hard exclusive processes on spin-1/2 nucleon are described by four leadingtwist GPDs (H , E, H , and E), while certain experimental observables require a consideration of highertwist contributions as well.
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