Coherent photoproduction of pi(0)- and eta-mesons off Li-7

Crystal Ball MAMI Collaboration, Crystal Ball TAPS Collaboration, Crystal Ball A2 Collaboration, Y. Maghrbi*, B. Krusche, J. Ahrens, J. R. M. Annand, H. J. Arends, R. Beck, V. Bekrenev, B. Boillat, A. Braghieri, D. Branford, W. J. Briscoe, J. Brudvik, S. Cherepnya, R. F. B. Codling, E. J. Downie, P. Drexler, L. V. Fil'kovA. Fix, D. I. Glazier, R. Gregor, E. Heid, D. Hornidge, I. Jaegle, O. Jahn, V. L. Kashevarov, I. Keshelashvili, A. Knezevic, R. Kondratiev, M. Korolija, D. Krambrich, M. Lang, V. Lisin, K. Livingston, S. Lugert, I. J. D. MacGregor, D. M. Manley, M. Martinez, J. C. McGeorge, D. Mekterovic, V. Metag, B. M. K. Nefkens, A. Nikolaev, R. Novotny, M. Ostrick, P. Pedroni, F. Pheron, A. Polonski, S. Prakhov, J. W. Price, D. P. Watts

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

Coherent photoproduction of pi(0)-mesons from threshold (E-th approximate to 136 MeV) throughout the Delta-resonance region and of eta-mesons close to the production threshold (E-th approximate to 570 MeV for eta) has been measured for Li-7 nuclei. The experiment was performed using the tagged-photon beam of the Mainz MAMI accelerator with the Crystal Ball and TAPS detectors combined to give an almost 4 pi solid-angle electromagnetic calorimeter. The reactions were identified by a combined invariant-mass and missing-energy analysis. A comparison of the pion data to plane-wave impulse modelling tests the nuclear mass form factor. So far coherent eta production had been only identified for the lightest nuclear systems (H-2 and He-3). For He-3 a large enhancement of the cross section above plane-wave approximations had been reported, indicating the formation of a quasi-bound state. The present Li data for eta production agree with a plane-wave approximation. Contrary to He-3, neither a threshold enhancement of the total cross section nor a deviation of the angular distributions from the expected form factor dependence were observed.

Original languageEnglish
Article number38
Number of pages14
JournalEuropean Physical Journal A: Hadrons and Nuclei
Volume49
Issue number3
DOIs
Publication statusPublished - Mar 2013

Keywords

  • NEAR-THRESHOLD PHOTOPRODUCTION
  • ELASTIC ELECTRON-SCATTERING
  • TAGGED PHOTON SPECTROMETER
  • EXCLUSIVE MEASUREMENT
  • NUCLEI
  • DEUTERON
  • PROTON
  • HE-4
  • PI(0)-PHOTOPRODUCTION
  • ELECTROPRODUCTION

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