[1] Univ Santiago de Compostela, Dept Fis Particulas, Santiago De Compostela 15782, Spain
[2] Univ Santiago de Compostela, IGFAE, Santiago De Compostela 15782, Spain
[3] CERN, Dept Phys, Theory Unit, CH-1211 Geneva 23, Switzerland
[4] CEA Saclay, IRFU, Serv Phys Particules, F-91191 Gif Sur Yvette, France
[5] Inst Nucl Phys PAN, PL-31342 Krakow, Poland
[6] Charles Univ Prague, Fac Math & Phys, CR-18000 Prague 8, Czech Republic