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

Abstract

The Born cross section of the e+e− → Λc+Λ¯c− process is measured with unprecedented precision using data collected with the BESIII detector at s=4574.5, 45580.0, 4590.0 and 4599.5 MeV. The non-zero cross section near the Λc+Λ¯c− production threshold is discerned. At center-of-mass energies s=4574.5 and 4599.5 MeV, the higher statistics data enable us to measure the Λc polar angle distributions. From these, the ratio between the Λc electric and magnetic form factors (|GE/GM|) 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.