Precision Measurement of the $e^{+}e^{-}~\rightarrow~Λ_{c}^{+} \barΛ_{c}^{-}$ Cross Section Near Threshold

Abstract

The Born cross section of the $e^{+}e^{-}~\rightarrow~Λ_{c}^{+} \barΛ_{c}^{-}$ 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 MeV. The non-zero cross section near the $\Lambda_{c}^{+} \bar{\Lambda}_{c}^{-}$ production threshold is discerned. 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 ratio between the $\Lambda_{c}$ electric and magnetic form factors ($|G_{E}/G_{M}|$) is 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.