Optimal observable analysis for the decay plus missing energy Zaineb Calcuttawala, Anirban Kundu, Soumitra Nandi and Sunando Kumar Patra Eur. Phys. J. C, 77 9 (2017) 650 Published online: 26 September 2017 DOI: 10.1140/epjc/s10052-017-5227-5