1. Faculty of Science, Šafárik University, Moyzesova 16, 040 01 Košice, Slovakia
2. Bogolyubov Laboratory of Theoretical Physics, Joint Institute for Nuclear Research, 141980 Dubna, Russia
3. Institute of Experimental Physics, Slovak Academy of Sciences, Watsonova 47, 040 01 Košice, Slovakia
4. Department of Physics, University of Helsinki, FI-00014 Helsinki, Finland