; Ciullo, G. ; Contalbrigo, M. ; Dalpiaz, P. F. ; Deconinck, W.
; De Leo, R. ; De Sanctis, E. ; Diefenthaler, M. ; Di Nezza, P. ; Düren, M. ; Ehrenfried, M. ; Elbakian, G. ; Ellinghaus, F.
; Etzelmüller, E. ; Fabbri, R. ; Felawka, L. ; Frullani, S. ; Gabbert, D. ; Gapienko, G. ; Gapienko, V. ; Garibaldi, F. ; Gavrilov, G. ; Gharibyan, V. ; Hartig, M. ; Hasch, D. ; Holler, Y. ; Hristova, I. ; Ivanilov, A. ; Jackson, H. E. ; Joosten, S. ; Kaiser, R. ; Karyan, G. ; Keri, T. ; Kinney, E. ; Kisselev, A. ; Korotkov, V. ; Kozlov, V. ; Kravchenko, P. ; Krivokhijine, V. G. ; Lagamba, L.
; Lapikás, L. ; Lehmann, I. ; Lenisa, P. ; Lorenzon, W. ; Ma, B.-Q. ; Mahon, D. ; Manaenkov, S. I. ; Mao, Y. ; Marianski, B. ; Marukyan, H. ; Movsisyan, A. ; Murray, M. ; Naryshkin, Y. ; Nass, A. ; Nowak, W.-D. ; Pappalardo, L. L. ; Perez-Benito, R. ; Petrosyan, A. ; Reimer, P. E.
; Reolon, A. R. ; Riedl, C. ; Rith, K. ; Rostomyan, A. ; Ryckbosch, D. ; Schäfer, A. ; Schnell, G. ; Schüler, K. P. ; Seitz, B. ; Shibata, T.-A. ; Stahl, M. ; Stancari, M. ; Statera, M. ; Steffens, E. ; Steijger, J. J. M. ; Taroian, S. ; Terkulov, A.
; Truty, R. ; Trzcinski, A. ; Tytgat, M.
; Van Haarlem, Y. ; Van Hulse, C. ; Vikhrov, V. ; Vilardi, I. ; Wang, S. ; Yaschenko, S. ; Yen, S. ; Zeiler, D. ; Zihlmann, B. ; Zupranski, P. | Item type: | Article | ||||
|---|---|---|---|---|---|
| Journal or Publication Title: | The European Physical Journal C | ||||
| Publisher: | SPRINGER | ||||
| Place of Publication: | NEW YORK | ||||
| Volume: | 74 | ||||
| Number of Issue or Book Chapter: | 11 | ||||
| Date: | 2014 | ||||
| Institutions: | Physics > Institute of Theroretical Physics > Chair Professor Schäfer > Group Andreas Schäfer | ||||
| Identification Number: |
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| Keywords: | MESON PRODUCTION; | ||||
| Dewey Decimal Classification: | 500 Science > 530 Physics | ||||
| Status: | Published | ||||
| Refereed: | Yes, this version has been refereed | ||||
| Created at the University of Regensburg: | Yes | ||||
| Item ID: | 60974 |
Web of ScienceAbstract
Exclusive electroproduction of. mesons on unpolarized hydrogen and deuterium targets is studied in the kinematic region of Q(2) > 1.0 GeV2, 3.0 GeV < W < 6.3 GeV, and -t ' < 0.2 GeV2. Results on the angular distribution of the omega meson, including its decay products, are presented. The data were accumulated with the HER-MES forward spectrometer during the 1996-2007 running period using the 27.6 ...

Abstract
Exclusive electroproduction of. mesons on unpolarized hydrogen and deuterium targets is studied in the kinematic region of Q(2) > 1.0 GeV2, 3.0 GeV < W < 6.3 GeV, and -t ' < 0.2 GeV2. Results on the angular distribution of the omega meson, including its decay products, are presented. The data were accumulated with the HER-MES forward spectrometer during the 1996-2007 running period using the 27.6 GeV longitudinally polarized electron or positron beam of HERA. The determination of the virtual-photon longitudinal-to-transverse cross-section ratio reveals that a considerable part of the cross section arises from transversely polarized photons. Spin density matrix elements are presented in projections of Q(2) or -t '. Violation of s-channel helicity conservation is observed for some of these elements. Asizable contribution from unnatural-parity-exchange amplitudes is found and the phase shift between those amplitudes that describe transverse omega production by longitudinal and transverse virtual photons,gamma(L)* -> omega(T) and gamma(T)* -> omega(T), is determined for the first time. A hierarchy of helicity amplitudes is established, which mainly means that the unnatural-parity-exchange amplitude describing the gamma(T)* -> omega(T) transition dominates over the two natural-parity-exchange amplitudes describing the gamma(L)* -> omega(L) and gamma(T)* -> omega(T) transitions, with the latter two being of similar magnitude. Good agreement is found between the HERMES proton data and results of a pQCD-inspired phenomenological model that includes pion-pole contributions, which are of unnatural parity.
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