Using $e^{+}{e}^{-}$ collision data collected with the BESIII detector operating at the BEPCII collider, the Born cross sections of $e^{+}{e}^{-}\to {\mathrm{\Lambda }}_c^{+}{\overline{\mathrm{\Lambda }}}_c(2595{)}^{-}+\mathrm{c}.\mathrm{c}.$ and $e^{+}{e}^{-}\to {\mathrm{\Lambda }}_c^{+}{\overline{\mathrm{\Lambda }}}_c(2625{)}^{-}+\mathrm{c}.\mathrm{c}.$ are measured for the first time at center-of-mass energies of $\sqrt{s}=4918.0$ and 4950.9 MeV. Nonzero cross sections are observed very close to the production threshold. The measured Born cross sections of $e^{+}{e}^{-}\to {\mathrm{\Lambda }}_c^{+}{\overline{\mathrm{\Lambda }}}_c(2625{)}^{-}+\mathrm{c}.\mathrm{c}.$ are about 2–3 times greater than those of $e^{+}{e}^{-}\to {\mathrm{\Lambda }}_c^{+}{\overline{\mathrm{\Lambda }}}_c(2595{)}^{-}+\mathrm{c}.\mathrm{c}.$, providing the similar behavior as semileptonic decays of ${\mathrm{\Lambda }}_b^0$, but different behavior from that in the hadronic decays of ${\mathrm{\Lambda }}_b^0$. The Born cross sections are $15.6\pm 3.1\pm 0.9\mathrm{pb}$ and $29.4\pm 3.7\pm 2.7\mathrm{pb}$ for $e^{+}{e}^{-}\to {\mathrm{\Lambda }}_c^{+}{\overline{\mathrm{\Lambda }}}_c(2595{)}^{-}+\mathrm{c}.\mathrm{c}.$, and are $43.4\pm 4.0\pm 4.1\mathrm{pb}$ and $76.8\pm 6.5\pm 4.2\mathrm{pb}$ for $e^{+}{e}^{-}\to {\mathrm{\Lambda }}_c^{+}{\overline{\mathrm{\Lambda }}}_c(2625{)}^{-}+\mathrm{c}.\mathrm{c}.$ at $\sqrt{s}=4918.0$ and 4950.9 MeV, respectively. Based on the polar angle distributions of the ${\overline{\mathrm{\Lambda }}}_c(2625{)}^{-}$ and ${\mathrm{\Lambda }}_c(2625{)}^{+}$, the form-factor ratios $\sqrt{|G_E{|}^2+3|G_M{|}^2}/|G_C|$ are determined for $e^{+}{e}^{-}\to {\mathrm{\Lambda }}_c^{+}{\overline{\mathrm{\Lambda }}}_c(2625{)}^{-}+\mathrm{c}.\mathrm{c}.$ for the first time, which are $5.95\pm 4.07\pm 0.15$ and $0.94\pm 0.32\pm 0.02$ at $\sqrt{s}=4918.0$ and 4950.9 MeV, respectively. All of these first uncertainties are statistical and second systematic.

• Received 15 December 2023
• Accepted 2 April 2024

DOI:https://doi.org/10.1103/PhysRevD.109.L071104

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Published by the American Physical Society