Measurement of the η–η′ mixing angle in π − and K − beams with the GAMS-4π Spectrometer S. V. Donskov, V. N. Kolosov, A. A. Lednev, Yu. V. Mikhailov, V. A. Polyakov, V. D. Samoylenko and G. V. Khaustov Eur. Phys. J. C, 73 10 (2013) 2614 Published online: 24 October 2013 DOI: 10.1140/epjc/s10052-013-2614-4