1. Department of Physics, Taras Shevchenko National University of Kyiv, 03022 Kyiv, Ukraine
2. Bogolyubov Institute for Theoretical Physics, Kyiv 03680, Ukraine
3. Department of Physics, University of Oslo, POB 1048 Blindern, N-0316 Oslo, Norway
4. Skobeltsyn Institute of Nuclear Physics, Moscow State University, 119899 Moscow, Russia