Photoproduction of π0 mesons off protons and neutrons in the second and third nucleon resonance region

Dieterle, M. et al. (2018) Photoproduction of π0 mesons off protons and neutrons in the second and third nucleon resonance region. Physical Review C, 97, 065205. (doi:10.1103/PhysRevC.97.065205)

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{Photoproduction of mesons off quasi-free nucleons bound in the deuteron allows to study the electromagnetic excitation spectrum of the neutron and the isospin structure of the excitation of nucleon resonances. The database for such reactions is much more sparse than for free proton targets.} [Purpose] {Study experimentally single π 0 photoproduction off quasi-free nucleons from the deuteron. Investigate nuclear effects by a comparison of the results for free protons and quasi-free protons. Use the quasi-free neutron data (corrected for nuclear effects) to test the predictions of reaction models and partial wave analysis (PWA) for γ n → n π 0 derived from the analysis of the other isospin channels.} [Methods] {High statistics angular distributions and total cross sections for the photoproduction of π 0 mesons off the deuteron with coincident detection of recoil nucleons have been measured for the first time. The experiment was performed at the tagged photon beam of the Mainz MAMI accelerator for photon energies between 0.45~GeV and 1.4~GeV, using an almost 4 π electromagnetic calorimeter composed of the Crystal Ball and TAPS detectors. A complete kinematic reconstruction of the final state removed the effects of Fermi motion.} [Results] {Significant effects from final state interactions (FSI) were observed for participant protons in comparison to free proton targets (between 30\recoil neutrons were corrected for such effects under the assumption that they are identical for participant protons and neutrons. Reaction model predictions and PWA for γ n → n π 0 , based on fits to data for the other isospin channels, disagreed between themselves and no model provided a good description of the new data.} [Conclusions] {The results demonstrate clearly the importance of a mesurement of the fully neutral final state for the isospin decmposition of the cross section. Model refits, for example from the Bonn-Gatchina analysis, show that the new and the previous data for the other three isospin channels can be simultaneously described when the contributions of several partial waves are modified. The results are also relevant for the suppression of the higher resonance bumps in total photoabsorption on nuclei, which are not well understood.

Item Type:Articles
Additional Information:This work was supported by Schweizerischer Nationalfonds (200020- 156983, 132799, 121781, 117601), Deutsche Forschungsgemeinschaft (SFB 443, SFB 1044, SFB/TR16), the INFNItaly, the European Community-Research Infrastructure Activity under the FP7 programme (Hadron Physics, Grant Agreement No. 227431), the UK Science and Technology Facilities Council (ST/J000175/1, ST/G008604/1, ST/G008582/1,ST/J00006X/1, and ST/L00478X/1), and the Natural Sciences and Engineering Research Council (NSERC, FRN: SAPPJ-2015-00023), Canada. This material is based upon work also supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics Research Division, under Awards No. DE-FG02-99-ER41110, No. DEFG02-88ER40415, and No. DE-FG02-01-ER41194 and by the National Science Foundation under Grants No. PHY-1039130 and No. IIA-1358175.
Glasgow Author(s) Enlighten ID:McGeorge, Dr John and Werthmueller, Dr Dominik and Livingston, Dr Kenneth and Thiel, Dr Annika and MacGregor, Professor I and Annand, Dr John and Glazier, Dr Derek
Authors: Dieterle, M., Werthmueller, D., Abt, S., Afzal, F., Aguar Bartolome, P., Ahmed, Z., Ahrens, J., Annand, J.R.M., Arends, H.J., Bashkanov, M., Beck, R., Biroth, M., Borisov, N., Braghieri, A., Briscoe, W.J., Cherepnya, S., Cividini, F., Collicott, C., Costanza, S., Denig, A., Downie, E.J., Drexler, P., Filkov, L.V., Garni, S., Glazier, D.I., Gorodnov, I., Gradl, W., Gunther, M., Gurevich, D., Heijkenskjold, L., Hornidge, D., Huber, G.M., Kaser, A., Kashevarov, V.L., Kay, S., Keshelashvili, I., Kondratiev, R., Korolija, M., Krusche, B., Lazarev, A., Lisin, V., Livingston, K., Lutterer, S., MacGregor, I.J.D., Manley, D.M., Martel, P.P., McGeorge, J.C., Metag, V., Middleton, D.G., Miskimen, R., Mornacchi, E., Mushkarenkov, A., Neganov, A., Neiser, A., Oberle, M., Ostrick, M., Otte, P.B., Oussena, B., Paudyal, D., Pedroni, P., Polonski, A., Prakhov, S.N., Ron, G., Rostomyan, T., Sarty, A., Sfienti, C., Sokhoyan, V., Spieker, K., Steffen, O., Strakovsky, I.I., Strub, T., Supek, I., Thiel, A., Thiel, M., Thomas, A., Unverzagt, M., Usov, Y. A., Wagner, S., Walford, N.K., Watts, D.P., Wettig, J., Witthauer, L., Wolfes, M., and Zana, L.A.
College/School:College of Science and Engineering > School of Physics and Astronomy
Journal Name:Physical Review C
Publisher:American Physical Society
ISSN (Online):1089-490X

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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
570711Nuclear Physics GroupDavid IrelandScience & Technology Facilities Council (STFC)ST/J000175/1P&A - PHYSICS & ASTRONOMY
507271Illuminating strongly interacting matterI MacgregorScience & Technology Facilities Council (STFC)ST/G008604/1P&A - PHYSICS & ASTRONOMY