Insight into the Narrow Structure in η Photoproduction on the Neutron from Helicity-Dependent Cross Sections

L. Witthauer, M. Dieterle, S. Abt, P. Achenbach, F. Afzal, Z. Ahmed, J. R.M. Annand, H. J. Arends, M. Bashkanov, R. Beck, M. Biroth, N. S. Borisov, A. Braghieri, W. J. Briscoe, F. Cividini, S. Costanza, C. Collicott, A. Denig, E. J. Downie, P. DrexlerM. I. Ferretti-Bondy, S. Gardner, S. Garni, D. I. Glazier, D. Glowa, W. Gradl, M. Günther, G. M. Gurevich, D. Hamilton, D. Hornidge, G. M. Huber, A. Käser, V. L. Kashevarov, S. Kay, I. Keshelashvili, R. Kondratiev, M. Korolija, B. Krusche*, A. B. Lazarev, J. M. Linturi, V. Lisin, K. Livingston, S. Lutterer, I. J.D. Macgregor, J. Mancell, D. M. Manley, P. P. Martel, V. Metag, W. Meyer, R. Miskimen, E. Mornacchi, A. Mushkarenkov, A. B. Neganov, A. Neiser, M. Oberle, M. Ostrick, P. B. Otte, D. Paudyal, P. Pedroni, A. Polonski, S. N. Prakhov, A. Rajabi, G. Reicherz, G. Ron, T. Rostomyan, A. Sarty, C. Sfienti, M. H. Sikora, V. Sokhoyan, K. Spieker, O. Steffen, I. I. Strakovski, Th Strub, I. Supek, A. Thiel, M. Thiel, M. Unverzagt, Yu A. Usov, S. Wagner, N. K. Walford, D. P. Watts, D. Werthmüller, J. Wettig, M. Wolfes, L. Zana

*Corresponding author for this work

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Abstract

The double polarization observable E and the helicity dependent cross sections σ1/2 and σ3/2 were measured for η photoproduction from quasifree protons and neutrons. The circularly polarized tagged photon beam of the A2 experiment at the Mainz MAMI accelerator was used in combination with a longitudinally polarized deuterated butanol target. The almost 4π detector setup of the Crystal Ball and TAPS is ideally suited to detect the recoil nucleons and the decay photons from η→2γ and η→3π0. The results show that the narrow structure previously observed in η photoproduction from the neutron is only apparent in σ1/2 and hence, most likely related to a spin-1/2 amplitude. Nucleon resonances that contribute to this partial wave in η production are only N 1/2- (S11) and N 1/2+ (P11). Furthermore, the extracted Legendre coefficients of the angular distributions for σ1/2 are in good agreement with recent reaction model predictions assuming a narrow resonance in the P11 wave as the origin of this structure.

Original languageEnglish
Article number132502
JournalPhysical Review Letters
Volume117
Issue number13
DOIs
Publication statusPublished - 22 Sept 2016

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