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The process $e^{+}e^{-}\rightarrow\Lambda\bar{\Lambda}$ is studied using datasamples at $\sqrt{s}=2.2324$, 2.400, 2.800 and 3.080 GeV collected with theBESIII detector operating at the BEPCII collider. The Born cross section ismeasured at $\sqrt{s}$=2.2324 GeV, which is 1.0 MeV above the$\Lambda\bar{\Lambda}$ mass threshold, to be $305\pm45^{+66}_{-36}$ pb, wherethe first uncertainty is statistical and the second systematic. The substantialcross section near threshold is significantly larger than that expected fromtheory, which predicts the cross section to vanish at threshold. The Born crosssections at $\sqrt{s}$=2.400, 2.800 and 3.080 GeV are measured and found to beconsistent with previous experimental results, but with improved precision.Finally, the corresponding effective electromagnetic form factors of $\Lambda$are deduced.

Observation of a cross-section enhancement near mass threshold in $e^{+}e^{-}\rightarrow\Lambda\bar{\Lambda}$