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Spin density matrix elements in exclusive ω electroproduction on ¹H and ²H targets at 27.5 GeV beam energy

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HERMES
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.
Keywords
PARTON DISTRIBUTIONS, QCD, VIRTUAL COMPTON-SCATTERING, VECTOR-MESON LEPTOPRODUCTION

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Chicago
Airapetian, A, N Akopov, Z Akopov, W Augustyniak, A Avetissian, HP Blok, A Borissov, et al. 2014. “Spin Density Matrix Elements in Exclusive ω Electroproduction on 1H and 2H Targets at 27.5 GeV Beam Energy.” European Physical Journal C 74 (11).
APA
Airapetian, A., Akopov, N., Akopov, Z., Augustyniak, W., Avetissian, A., Blok, H., Borissov, A., et al. (2014). Spin density matrix elements in exclusive ω electroproduction on 1H and 2H targets at 27.5 GeV beam energy. EUROPEAN PHYSICAL JOURNAL C, 74(11).
Vancouver
1.
Airapetian A, Akopov N, Akopov Z, Augustyniak W, Avetissian A, Blok H, et al. Spin density matrix elements in exclusive ω electroproduction on 1H and 2H targets at 27.5 GeV beam energy. EUROPEAN PHYSICAL JOURNAL C. 2014;74(11).
MLA
Airapetian, A, N Akopov, Z Akopov, et al. “Spin Density Matrix Elements in Exclusive ω Electroproduction on 1H and 2H Targets at 27.5 GeV Beam Energy.” EUROPEAN PHYSICAL JOURNAL C 74.11 (2014): n. pag. Print.
@article{5983032,
  abstract     = {Exclusive electroproduction of. mesons on unpolarized hydrogen and deuterium targets is studied in the kinematic region of Q(2) {\textrangle} 1.0 GeV2, 3.0 GeV {\textlangle} W {\textlangle} 6.3 GeV, and -t ' {\textlangle} 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)* -{\textrangle} omega(T) and gamma(T)* -{\textrangle} 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)* -{\textrangle} omega(T) transition dominates over the two natural-parity-exchange amplitudes describing the gamma(L)* -{\textrangle} omega(L) and gamma(T)* -{\textrangle} 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.},
  articleno    = {3110},
  author       = {Airapetian, A and Akopov, N and Akopov, Z and Augustyniak, W and Avetissian, A and Blok, HP and Borissov, A and Bryzgalov, V and Capiluppi, M and Capitani, GP and Cisbani, E and Ciullo, G and Contalbrigo, M and Dalpiaz, PF and Deconinck, W and De Leo, R and De Sanctis, E and Diefenthaler, M and Di Nezza, P and D{\"u}ren, M and Ehrenfried, M and Elbakian, G and Ellinghaus, F and Etzelm{\"u}ller, E and Fabbri, R and Felawka, L and Frullani, S and Gabbert, D and Gapienko, G and Gapienko, V and Garibaldi, F and Gavrilov, G and Gharibyan, V and Hartig, M and Hasch, D and Holler, Y and Hristova, I and Ivanilov, A and Jackson, HE and Joosten, S and Kaiser, R and Karyan, G and Keri, T and Kinney, E and Kisselev, A and Korotkov, V and Kozlov, V and Kravchenko, P and Krivokhijine, VG and Lagamba, L and Lapik{\'a}s, L and Lehmann, I and Lenisa, P and Lorenzon, W and Ma, BQ and Mahon, D and Manaenkov, SI and Mao, Y and Marianski, B and Marukyan, H and Movsisyan, A and Murray, M and Naryshkin, Y and Nass, A and Nowak, WD and Pappalardo, LL and Perez-Benito, R and Petrosyan, A and Reimer, PE and Reolon, AR and Riedl, C and Rith, K and Rostomyan, A and Ryckbosch, Dirk and Sch{\"a}fer, A and Schnell, G and Sch{\"u}ller, KP and Seitz, B and Shibata, TA and Stahl, M and Stancari, M and Statera, M and Steffens, E and Steijger, JJM and Taroian, S and Terkulov, A and Truty, R and Trzcinski, A and Tytgat, Michael and Van Haarlem, Y and VanHulse, C and Vikhrov, V and Vilardi, I and Wang, S and Yaschenko, S and Yen, S and Zeiler, D and Zihlmann, B and Zupranski, P},
  issn         = {1434-6044},
  journal      = {EUROPEAN PHYSICAL JOURNAL C},
  language     = {eng},
  number       = {11},
  pages        = {25},
  title        = {Spin density matrix elements in exclusive \ensuremath{\omega} electroproduction on {\textonesuperior}H and {\texttwosuperior}H targets at 27.5 GeV beam energy},
  url          = {http://dx.doi.org/10.1140/epjc/s10052-014-3110-1},
  volume       = {74},
  year         = {2014},
}

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