1. Adlarson, P., et al., WASA-at-COSY Collaboration: Phys. Rev. Lett. 106, 242302 (2011), and arXiv: 1409.2659 . See also the preceding reports: Clement, H., et al., CELSIUS-WASA Collaboration: Prog. Part. Nucl. Phys. 61, 276 (2008); Bashkanov, M., et al., CELSIUS/WASA Collaboration: Phys. Rev. Lett. 102, 052301 (2009)
2. Adlarson, P., et al., WASA-at-COSY Collaboration: Phys. Lett. B 721, 229 (2013)
3. Adlarson, P., et al., WASA-at-COSY Collaboration, SAID Data Analysis Center: Phys. Rev. C 90, 035204 (2014). See also Adlarson, P., et al., WASA-at-COSY Collaboration, SAID Data Analysis Center: Phys. Rev. Lett. 112, 202301 (2014)
4. Dyson, F.J., Xuong, N.-H.: Phys. Rev. Lett. 13, 815 (1964)
5. Mulders, P.J., Aerts, A.T., de Swart, J.J.: Phys. Rev. D 21, 2653 (1980); Oka, M., Yazaki, K.: Phys. Lett. B 90, 41 (1980); Cvetič, M., Golli, B., Mankoč-Borštnik, N., Rosina, M.: Phys. Lett. B 93, 489 (1980); Mulders, P.J., Thomas, A.W.: J. Phys. G 9, 1159 (1983); Maltman, K.: Nucl. Phys. A 438, 669 (1985); Goldman, T., Maltman, K., Stephenson, G.J., Schmidt, K.E., Wang, F.: Phys. Rev. C 39, 1889 (1989); Yuan, X.Q., Zhang, Z.Y., Yu, Y.W., Shen, P.N.: Phys. Rev. C 60, 045203 (1999); Mota, R.D., Valcarce, A., Fernández, F., Entem, D.R., Garcilazo, H.: Phys. Rev. C 65, 034006 (2002); Ping, J.L., Huang, H.X., Pang, H.R., Wang, F., Wong, C.W.: Phys. Rev. C 79, 024001 (2009); Huang, H., Ping, J., Wang, F.: Phys. Rev. C 89, 034001 (2014)