Observation of ψ ( 3686 ) → n n ¯ and improved measurement of ψ ( 3686 ) → p p

• Published in: Physical review. D 2018-08, Vol.98 (3), Article 032006
• Main Authors: Ablikim, M., Achasov, M. N., Ahmed, S., Albrecht, M., Ambrose, D. J., Amoroso, A., An, F. F., An, Q., Bai, J. Z., Bakina, O., Baldini Ferroli, R., Ban, Y., Bennett, D. W., Bennett, J. V., Berger, N., Bertani, M., Bettoni, D., Bian, J. M., Bianchi, F., Boger, E., Boyko, I., Briere, R. A., Cai, H., Cai, X., Cakir, O., Calcaterra, A., Cao, G. F., Cetin, S. A., Chai, J., Chang, J. F., Chelkov, G., Chen, G., Chen, H. S., Chen, J. C., Chen, M. L., Chen, P. L., Chen, S. J., Chen, X. R., Chen, Y. B., Chu, X. K., Cibinetto, G., Dai, H. L., Dai, J. P., Dbeyssi, A., Dedovich, D., Deng, Z. Y., Denig, A., Denysenko, I., Destefanis, M., De Mori, F., Ding, Y., Dong, C., Dong, J., Dong, L. Y., Dong, M. Y., Dou, Z. L., Du, S. X., Duan, P. F., Fang, J., Fang, S. S., Fang, Y., Farinelli, R., Fava, L., Fegan, S., Feldbauer, F., Felici, G., Feng, C. Q., Fioravanti, E., Fritsch, M., Fu, C. D., Gao, Q., Gao, X. L., Gao, Y., Gao, Y. G., Gao, Z., Garzia, I., Goetzen, K., Gong, L., Gong, W. X., Gradl, W., Greco, M., Gu, M. H., Gu, Y. T., Guo, A. Q., Guo, R. P., Guo, Y. P., Haddadi, Z., Han, S., Hao, X. Q., Harris, F. A., He, K. L., He, X. Q., Heinsius, F. H., Held, T., Heng, Y. K., Holtmann, T., Hou, Z. L., Hu, H. M., Hu, T., Hu, Y.
• Format: Article
• Language: English
• Subjects: hadronic decays; NUCLEAR PHYSICS AND RADIATION PHYSICS; PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
• ISSN: 2470-0010; 2470-0029; 2470-0029
• DOI: 10.1103/PhysRevD.98.032006

Here, we observe the decay ψ(3686) → n$\bar{n}$ for the first time and measure ψ(3686) → p$\bar{p}$ with improved accuracy by using 1.07 × 108 ψ(3686) events collected with the BESIII detector. The measured branching fractions are $\mathscr{B}$(ψ(3686) → n$\bar{n}$) = (3.06 ± 0.06 ± 0.14) × 10-4 and $\mathscr{B}$(ψ(3686) → p$\bar{p}$) = (3.05±0.02±0.12) × 10-4. Here, the first uncertainties are statistical and the second ones systematic. With the hypothesis that the polar angular distributions of the neutron and proton in the center-of-mass system obey 1 + α cos2 θ, we determine the α parameters to be αn$\bar{n}$ = 0.68 ± 0.12 ± 0.11 and αp$\bar{p}$ = 1.03 ± 0.06 ± 0.03 for ψ(3686) → n$\bar{n}$ and ψ(3686) → p$\bar{p}$, respectively.