[1] Russian Acad Sci, Inst Nucl Res, 60th October Anniversary Prospect 7a, Moscow 117312, Russia
[2] Moscow Inst Phys & Technol, Inst Skii Per 9, Dolgoprudnyi 141700, Moscow Region, Russia
[3] Moscow MV Lomonosov State Univ, Fac Phys, Moscow 119991, Russia
[4] Univ Cambridge, Dept Appl Math & Theoret Phys, Wilberforce Rd, Cambridge CB3 0WA, England