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ISSN - 15507998, Physical Review D - Particles, Fields, Gravitation and Cosmology, 2012, vol. 86, p. -

Study of J/ψ→pp̄ and J/ψ→nn̄

Ablikim M., Achasov M. N., Ambrose D. J., An F. F., An Q., An Z. H., Bai J. Z., Ban Y., Becker J., Berger N., Bertani M., Bian J. M., Boger E., Bondarenko O., Boyko I., Briere R. A., Bytev V., Cai X., Calcaterra A., Cao G. F., Chang J. F., Chelkov G., Chen G., Chen H. S., Chen J. C., Chen M. L., Chen S. J., Chen Y., Chen Y. B., Cheng H. P., Chu Y. P., Cronin-Hennessy D., Dai H. L., Dai J. P., Dedovich D., Deng Z. Y., Denig A., Denysenko I., Destefanis M., Ding W. M., Ding Y., Dong L. Y., Dong M. Y., Du S. X., Fang J., Fang S. S., Fava L., Feldbauer F., Feng C. Q., Ferroli R. B., Fu C. D., Fu J. L., Gao Y., Geng C., Goetzen K., Gong W. X., Gradl W., Greco M., Gu M. H., Gu Y. T., Guan Y. H., Guo A. Q., Guo L. B., Guo Y. P., Han Y. L., Hao X. Q., Harris F. A., He K. L., He M., He Z. Y., Held T., Heng Y. K., Hou Z. L., Hu H. M., Hu J. F., Hu T., Huang B., Huang G. M., Huang J. S., Huang X. T., Huang Y. P., Hussain T., Ji C. S., Ji Q., Ji X. B., Ji X. L., Jia L. K., Jiang L. L., Jiang X. S., Jiao J. B., Jiao Z., Jin D. P., Jin S., Jing F. F., Kalantar-Nayestanaki N., Kavatsyuk M.

The decays J/ψ→pp̄ and J/ψ→nn̄ have been investigated with a sample of 225.2×106 J/ψ events collected with the BESIII detector at the BEPCII e +e - collider. The branching fractions are determined to be B(J/ψ→pp̄)=(2.112±0. 004±0.031)×10 -3 and B(J/ψ→nn̄)=(2. 07±0.01±0.17)×10 -3. Distributions of the angle θ between the proton or antineutron and the beam direction are well described by the form 1+α cos2θ, and we find α=0.595±0.012±0.015 for J/ψ→pp̄ and α=0.50±0.04±0.21 for J/ψ→nn̄. Our branching-fraction results suggest a large phase angle between the strong and electromagnetic amplitudes describing the J/ψ→NN̄ decay. © 2012 American Physical Society.