[1] Australian Natl Univ, Res Sch Phys & Engn, Ctr Antimatter Matter Studies, Canberra, ACT 0200, Australia
[2] Flinders Univ S Australia, Sch Chem Phys & Earth Sci, Ctr Antimatter Matter Studies, Adelaide, SA 5001, Australia
[3] Univ Malaya, Inst Math Sci, Kuala Lumpur 50603, Malaysia