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Measurement of the Electromagnetic Transition Form-factors in the decays \(η'\rightarrowπ^+π^-l^+l^-\)

By Besiii Collaboration and others
With a sample of \((10087\pm44)\times10^{6}\) \(J/\psi\) events accumulated with the BESIII detector, we analyze the decays \(\eta'\rightarrow\pi^+\pi^-l^+l^-(l=e,\) \(\mu)\) via the process \(J/\psi\rightarrow\gamma\eta'\). The branching fractions are measured to be \(\mathcal{B}(\eta'\rightarrow\pi^+\pi^-e^+e^-)=(2.45\pm0.02(\rm{stat.})\pm0.08(\rm{syst.})) \times10^{-3}\) and \(\mathcal{B}(\eta'\rightarrow\pi^+\pi^-\mu^+\mu^-)=(2.16\pm0.12(\rm{stat.})\pm0.06(\rm{syst.}))\times10^{-5}\), and the ratio is \(\frac{\mathcal{B}(\eta'\rightarrow\pi^{+}\pi^{-}e^{+}e^{-})}{\mathcal{B}(\eta'\rightarrow\pi^{+}\pi^{-}\mu^{+}\mu^{-})} = 113.4\pm0.9(\rm{stat.})\pm3.7(\rm{syst.})\). In addition, by combining the \(\eta'\rightarrow\pi^+\pi^-e^+e^-\) and \(\eta'\rightarrow\pi^+\pi^-\mu^+\mu^-\) decays, the... Show more
February 3, 2024
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