Understanding the internal structures of X(4140), X(4274), X(4500) and X(4700) Hua-Xing Chen, Er-Liang Cui, Wei Chen, Xiang Liu and Shi-Lin Zhu Eur. Phys. J. C, 77 3 (2017) 160 Published online: 15 March 2017 DOI: 10.1140/epjc/s10052-017-4737-5