Precision Measurement of the ${e}^{+}{e}^{-}\to {\Lambda }_{c}^{+}{\overline{\Lambda }}_{c}^{-}$ Cross Section Near Threshold

The cross section of the ${e}^{+}{e}^{-}\to {\Lambda }_{c}^{+}{\overline{\Lambda }}_{c}^{-}$ 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 ${\Lambda }_{c}^{+}{\overline{\Lambda }}_{c}^{-}$ 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 ${\Lambda }_{c}$ polar angle distributions. From these, the ${\Lambda }_{c}$ electric over magnetic form-factor ratios ($|{G}_{E}/{G}_{M}|$) are measured for the first time. They are found to be $1.14±0.14±0.07$ and $1.23±0.05±0.03$, respectively, where the first uncertainties are statistical and the second are systematic.