Study of spin-density matrix in exclusive electroproduction of ω meson at HERMES

16th Workshop on High Energy Spin Physics

Manaenkov, S.I.^1

National Research Center Kurchatov Institute, Petersburg Nuclear Physics Institute, Russia^1

关键词: Electroproduction;    Forward spectrometer;    Helicity conservation;    Polarized electrons;    Polarized photons;    Positron beams;    Spin density matrix;    Virtual photons;   

Others  :  https://iopscience.iop.org/article/10.1088/1742-6596/678/1/012043/pdf
DOI  :  10.1088/1742-6596/678/1/012043

来源: IOP

【 摘 要 】

Exclusive electroproduction of ω mesons on unpolarized hydrogen and deuterium targets is studied in the kinematic region of Q2> 1.0 GeV2, 3.0 GeV 2. The data were accumulated with the HERMES forward spectrometer during the 1996-2007 running period using the 27.6 GeV longitudinally polarized electron or positron beam of HERA. Spin-density matrix elements are presented in projections of Q2or -t'. Violation of s-channel helicity conservation is observed for some of these elements. A sizable contribution from unnatural-parity-exchange amplitudes is established for special combinations of spin-density matrix elements. The determination of the virtual-photon longitudinal-to- transverse cross-section ratio reveals that a dominant part of the cross section arises from transversely polarized photons. Good agreement is found between the HERMES proton data and results of a pQCD-inspired Goloskokov-Kroll model that includes pion-pole contributions.