Precision measurement of the $e^{+}{e}^{-}\to {\mathrm{\Lambda }}_c^{+}{\bar{\mathrm{\Lambda }}}_c^{-}$ cross section near threshold

The Born cross section of the $e^{+}e^{-}~\rightarrow~\Lambda_{c}^{+} \bar{\Lambda}_{c}^{-}$ process is measured with unprecedented precision using data collected with the BESIII detector at $\sqrt{s}=4574.5$, $45580.0$, $4590.0$ and $4599.5$ $\mathrm{M}\mathrm{e}\mathrm{V}$. The non-zero cross section near the ${\mathrm{\Lambda }}_c^{+}{\bar{\mathrm{\Lambda }}}_c^{-}$ production threshold is discerned. At center-of-mass energies $\sqrt{s}=4574.5$ and $4599.5$ $\mathrm{M}\mathrm{e}\mathrm{V}$, the higher statistics data enable us to measure the ${\mathrm{\Lambda }}_c$ polar angle distributions. From these, the ratio between the ${\mathrm{\Lambda }}_c$ electric and magnetic form factors ($\mathrm{\mid }{G}_E\mathrm{/}{G}_M\mathrm{\mid }$) is 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.