Coherent p0 electroproduction from the Deuteron

Harald Merkel

Institut für Kernphysik, Johannes Gutenberg-Universität Mainz

In this talk our recent measurements[1] on coherent threshold pion production from the Deuteron will be presented. The complete CMS solid angle was covered from threshold up to 4 MeV above threshold. By measuring at three different values of the virtual photon polarization, a transverse-longitudinal separation could be performed.

While the results of photoproduction experiments[2] are in reasonable agreement with predictions of Chiral Perturbation Theopy[3] (ChPT), our measurment shows a surprising deviation of one order of magnitude from calculations in the framework of ChPT[4].

Selected References:

  1. I. Ewald et al., Phys. Lett. B 499/3-4 (2001) 238-244
  2. J.C. Bergstrom et al., Phys. Rev. C 57 6 (1998) 3203
  3. S.R. Beane et al., Nucl. Phys. A618, 381 (1997);
  4. V. Bernard et al., Phys. Rev. C61, 058201 (2000)