[1] Univ Cambridge, Dept Appl Math & Theoret Phys, Cambridge CB3 9EW, England
[2] Univ Freiburg, Fak Phys, D-79104 Freiburg, Germany
[3] Rutherford Appleton Lab, Didcot OX11 0QX, Oxon, England
[4] Univ Montpellier 2, CNRS, UMR 5825, Lab Phys Math & Theor, F-34095 Montpellier 5, France
[5] Univ Oxford, Nucl Phys Lab, Oxford OX1 3RH, England
[6] Univ Cambridge, Cavendish Lab, Cambridge CB3 OHE, England
[7] DESY, D-22603 Hamburg, Germany
[8] Univ London, Royal Holloway & Bedford New Coll, Dept Phys, Egham TW20 0EX, Surrey, England
[9] Univ Warsaw, Inst Fizyki Teoretycznej, PL-00681 Warsaw, Poland
[10] Univ Michigan, Randall Lab Phys, Ann Arbor, MI 48109 USA
[11] Univ Manchester, Schuster Lab, Dept Phys & Astron, Manchester M13 9PL, Lancs, England
[12] Univ Southampton, Dept Phys & Astron, Southampton, Hants, England
[13] CERN, Div Theory, CH-1211 Geneva 23, Switzerland
[14] Univ Liverpool, Oliver Lodge Lab, Dept Phys, Liverpool L69 3BX, Merseyside, England
[15] Univ Oxford, Dept Theoret Phys, Oxford OX1 3NP, England
[16] Univ Hamburg, Inst Theoret Phys, D-22761 Hamburg, Germany
[17] Univ Glasgow, Dept Phys & Astron, Glasgow G12 8QQ, Lanark, Scotland
[18] Fermi Natl Accelerator Lab, Batavia, IL 60510 USA