Spin rotation effects in diffractive electroproduction of heavy quarkonia Michal Krelina, Jan Nemchik, Roman Pasechnik and Jan Čepila Eur. Phys. J. C, 79 2 (2019) 154 Published online: 20 February 2019 DOI: 10.1140/epjc/s10052-019-6666-y