Study of $J/{\psi}{\rightarrow}p\bar{p}$ and $J/{\psi}{\rightarrow}n\bar{n}$

Abstract
The decays $J/{\psi}{\rightarrow}p\bar{p}$ and $J/{\psi}{\rightarrow}n\bar{n}$ have been investigated with a sample of $225.2×10^6$ $J/{\psi}$ events collected with the BESIII detector at the BEPCII $e^+e^-$ collider. The branching fractions are determined to be $\mathscr{B}(J/{\psi}{\rightarrow}p\bar{p})=(2.112±0. 004±0.031)×10^{-3}$ and $\mathscr{B}(J/{\psi}{\rightarrow}n\bar{n})=(2.07±0.01±0.17)×10^{-3}$. Distributions of the angle $\theta$ between the proton or antineutron and the beam direction are well described by the form $1+\alpha cos2\theta$, and we find $\theta=0.595±0.012±0.015$ for $J/{\psi}{\rightarrow}p\bar{p}$ and $\theta=0.50±0.04±0.21$ for $J/{\psi}{\rightarrow}n\bar{n}$. Our branching-fraction results suggest a large phase angle between the strong and electromagnetic amplitudes describing the $J/{\psi}{\rightarrow}N\bar{N}$ decay.
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Ablikim, M., Achasov, M. N., Ambrose, D. J., An, F. F., An, Q., An, Z. H., . . . Zuo, J. X. (2012). Study of $J/{\psi}{\rightarrow}p\bar{p}$ and $J/{\psi}{\rightarrow}n\bar{n}$. Physical Review D - Particles, Fields, Gravitation and Cosmology, 86(3), 032014. http://dx.doi.org/10.1103/PhysRevD.86.032014
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© 2012 American Physical Society.
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