1. MTA-DE Research Group in Particle Physics, P. O. Box 51, H-4001 Debrecen, Hungary
2. Missouri University of Science and Technology, Rolla, Missouri 65409, USA
3. Institute for Particle and Nuclear Physics, Wigner Research Centre for Physics, Hungarian Academy of Sciences, Hungary
4. Institute of Nuclear Research of the Hungarian Academy of Sciences, Hungary
5. Institute of Physics, University of Debrecen, P. O. Box 105, H-4010 Debrecen, Hungary