Helicity amplitudes for photoexcitation of nucleon resonances off neutrons A. V. Anisovich, V. Burkert, E. Klempt, V. A. Nikonov, A. V. Sarantsev and U. Thoma Eur. Phys. J. A, 49 6 (2013) 67 Published online: 07 June 2013 DOI: 10.1140/epja/i2013-13067-x