Helicity-dependent cross sections and double-polarization observable E in η photoproduction from quasifree protons and neutrons

Witthauer, L. and Dieterle, M. and Abt, S. and Achenbach, P. and Afzal, F. and Ahmed, Z. and Akondi, C. S. and Annand, J. R. M. and Arends, H. J. and Bashkanov, M. and Beck, R. and Biroth, M. and Borisov, N. S. and Braghieri, A. and Briscoe, W. J. and Cividini, F. and Costanza, S. and Collicott, C. and Denig, A. and Downie, E. J. and Drexler, P. and Ferretti-Bondy, M. I. and Gardner, S. and Garni, S. and Glazier, D. I. and Glowa, D. and Gradl, W. and Gunther, M. and Gurevich, G. M. and Hamilton, D. and Hornidge, D. and Huber, G. M. and Kaeser, A. and Kashevarov, V. L. and Kay, S. and Keshelashvili, I. and Kondratiev, R. and Korolija, M. and Krusche, B. and Lazarev, A. B. and Linturi, J. M. and Lisin, V. and Livingston, K. and Lutterer, S. and MacGregor, I. J. D. and Mancell, J. and Manley, D. M. and Martel, P. P. and Metag, V. and Meyer, W. and Miskimen, R. and Mornacchi, E. and Mushkarenkov, A. and Neganov, A. B. and Neiser, A. and Oberle, M. and Ostrick, M. and Otte, P. B. and Paudyal, D. and Pedroni, P. and Polonski, A. and Prakhov, S. N. and Rajabi, A. and Reicherz, G. and Ron, G. and Rostomyan, T. and Sarty, A. and Sfienti, C. and Sikora, M. H. and Sokhoyan, V. and Spieker, K. and Steffen, O. and Strakovsky, I. I. and Strub, Th. and Supek, I. and Thiel, A. and Thiel, M. and Thomas, A. and Unverzagt, M. and Usov, Yu. A. and Wagner, S. and Walford, N. K. and Watts, D. P. and Werthmueller, D. and Wettig, J. and Wolfes, M. and Zana, L.. (2017) Helicity-dependent cross sections and double-polarization observable E in η photoproduction from quasifree protons and neutrons. Physical Review C, 95 (5). 055201.

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Precise helicity-dependent cross sections and the double-polarization observable E were measured for η photoproduction from quasifree protons and neutrons bound in the deuteron. The η→2γ and η→3π0→6γ decay modes were used to optimize the statistical quality of the data and to estimate systematic uncertainties. The measurement used the A2 detector setup at the tagged photon beam of the electron accelerator MAMI in Mainz. A longitudinally polarized deuterated butanol target was used in combination with a circularly polarized photon beam from bremsstrahlung of a longitudinally polarized electron beam. The reaction products were detected with the electromagnetic calorimeters Crystal Ball and TAPS, which covered 98% of the full solid angle. The results show that the narrow structure observed earlier in the unpolarized excitation function of η photoproduction off the neutron appears only in reactions with antiparallel photon and nucleon spin (σ1/2). It is absent for reactions with parallel spin orientation (σ3/2) and thus very probably related to partial waves with total spin 1/2. The behavior of the angular distributions of the helicity-dependent cross sections was analyzed by fitting them withLegendre polynomials. The results are in good agreement with a model from the Bonn-Gatchina group, which uses an interference of P11 and S11 partial waves to explain the narrow structure.
Faculties and Departments:05 Faculty of Science > Departement Physik > Physik > Hadronenphysik (Krusche)
UniBasel Contributors:Krusche, Bernd
Item Type:Article, refereed
Article Subtype:Research Article
Publisher:American Physical Society
Note:Publication type according to Uni Basel Research Database: Journal article
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Last Modified:15 Jan 2018 13:57
Deposited On:15 Jan 2018 13:57

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