1. Skobeltsyn Institute of Nuclear Physics of Moscow State University, Moscow, RU-119234, Russia
2. Institute of Applied Physics of Irkutsk State University, Irkutsk, RU-664003, Russia
3. Institute for Nuclear Research of Russian Academy of Sciences, Moscow, RU-117312, Russia
4. Institute of Terrestrial Magnetism, Ionosphere and Radiowave Propagation of Russian Academy of Sciences (IZMIRAN), Troitsk, Moscow Region, 142092, Russia
5. Deutsches Elektronen Synchrotron (DESY), Zeuthen, D-15738, Germany
6. Dipartimento di Fisica Generale Universitá di Torino and INFN, Torino, I-10125, Italy