- 
								[1]
								M. Bashkanov et al, Phys. Rev. Lett., 102: 052301 (2009) 
- 
								[2]
								P. Adlarson et al, Phys. Rev. Lett., 106: 242302 (2011) 
- 
								[3]
								S. Keleta et al, Nucl. Phys. A, 825 71 (2009) 
- 
								[4]
								P. Adlarson et al (WASA-at-COSY Collaboration), Phys. Rev. C, 86: 032201 (2012) 
- 
								[5]
								P. Adlarson et al (WASA-at-COSY Collaboration), Phys. Rev. C, 88: 055208 (2013) 
- 
								[6]
								P. Adlarson et al (WASA-at-COSY Collaboration), Phys. Lett. B, 743: 325 (2015) 
- 
								[7]
								P. Adlarson et al (WASA-at-COSY Collaboration), Phys. Rev. C, 91: 015201 (2015) 
- 
								[8]
								P. Adlarson et al (WASA-at-COSY Collaboration), Phys. Rev. Lett., 112: 202301 (2014) 
- 
								[9]
								H. Clement, Progress in Particle and Nuclear Physics, 93: 195 (2017) 
- 
								[10]
								X. Q. Yuan, Z. Y. Zhang, Y. W. Yu, and P. N. Shen, Phys. Rev. C, 60: 045203 (1999) 
- 
								[11]
								M. Bashkanov, S. J. Brodsky, and H. Clement, Phys. Lett. B, 727: 438 (2013) 
- 
								[12]
								F. Huang, Z. Y. Zhang, P. N. Shen, and W. L. Wang, Chin. Phys. C, 39(7): 071001 (2015) 
- 
								[13]
								Y. B. Dong, P. N. Shen, F. Huang, and Z. Y. Zhang, Phys. Rev. C, 91(6): 064002 (2015) 
- 
								[14]
								Y. B. Dong, F. Huang, P. N. Shen, and Z. Y. Zhang, Phys. Rev. C, 94(1): 014003 (2016) 
- 
								[15]
								Y. B. Dong, F. Huang, P. N. Shen, and Z. Y. Zhang, Phys. Lett. B, 769: 223 (2017) 
- 
								[16]
								Y. B. Dong, F. Huang, P. N. Shen, and Z. Y. Zhang, Phys. Rev. D, 96: 094001 (2017) 
- 
								[17]
								A. Gal and H. Garcilazo, Phys. Rev. Lett., 111: 172301 (2013) 
- 
								[18]
								A. Gal and H. Garcilazo, Nucl. Phys. A, 928: 73 (2014) 
- 
								[19]
								C. Patrignani et al (Particle Data Group), Chin. Phys. C, 40(10): 100001 (2016) 
- 
								[20]
								E. Eichten, K. Gottfried, T. Kinoshita, K. D. Lane, and T. M. Yan, Phys. Rev. D, 21: 203 (1980) 
- 
								[21]
								Y. B. Ding, X. Q. Li, and P. N. Shen, Phys. Rev. D, 60: 074010 (1999) 
- 
								[22]
								Y. Lu, M. N. Anwar, and B. S. Zou, Phys. Rev. D, 94: 034021 (2016) 
- 
								[23]
								Y. Lu, M. N. Anwar, and B. S. Zou, Phys. Rev. D, 95: 034018 (2017) 
- 
								[24]
								F. Huang, P. N. Shen, Y. B. Dong, and Z. Y. Zhang, Sci. China Phys. Mech. Astron., 59(2): 622002 (2016) 
- 
								[25]
								D. M. Asner et al, Phys. Rev. D, 75: 012009 (2007) 
- 
								[26]
								J. P. Lees et al, Phys. Rev. D, 89: 111102 (R) (2014) 
- 
								[27]
								Private discussion with experimentalists