Study of B s →η c (J/ψ)D decay with perturbative QCD approach Junfeng Sun, Zhengjun Xiong, Yueling Yang and Gongru Lu Eur. Phys. J. C, 73 5 (2013) 2437 Published online: 22 May 2013 DOI: 10.1140/epjc/s10052-013-2437-3