The cross section of the $e^{+}{e}^{-}\to {\mathrm{\Lambda }}_c^{+}{\overline{\mathrm{\Lambda }}}_c^{-}$ process is measured with unprecedented precision using data collected with the BESIII detector at $\sqrt{s}=4574.5$, 4580.0, 4590.0 and 4599.5 MeV. The nonzero cross section near the ${\mathrm{\Lambda }}_c^{+}{\overline{\mathrm{\Lambda }}}_c^{-}$ production threshold is cleared. At center-of-mass energies $\sqrt{s}=4574.5$ and 4599.5 MeV, the higher statistics data enable us to measure the ${\mathrm{\Lambda }}_c$ polar angle distributions. From these, the ${\mathrm{\Lambda }}_c$ electric over magnetic form-factor ratios ($|G_E/G_M|$) are measured for the first time. They are found to be $1.14\pm 0.14\pm 0.07$ and $1.23\pm 0.05\pm 0.03$, respectively, where the first uncertainties are statistical and the second are systematic.

• Received 2 October 2017
• Revised 18 December 2017

DOI:https://doi.org/10.1103/PhysRevLett.120.132001

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Published by the American Physical Society