QCD sum rule study of hidden-charm pentaquarksHua-Xing Chen, Er-Liang Cui, Wei Chen, Xiang Liu, T. G. Steele and Shi-Lin ZhuEur. Phys. J. C, 76 10 (2016) 572DOI: https://doi.org/10.1140/epjc/s10052-016-4438-5