Measurement of A baryon polarization in e+ e- → Λ(Λ)over-bar at √s=3.773 GeV

Using a data sample of psi(3770) events collected with the BESIII detector at BEPCII corresponding to an integrated luminosity of 2.9 fb-1, we report a measurement of A spin polarization in e+ e- -> Lambda(Lambda) over bar at = root s = 3.773 GeV. The significance of polarization is found to be 2 sigma including the systematic uncertainty, which implies a zero phase between the transition amplitudes of the Lambda(Lambda) over bar helicity states. This phase can be interpreted in terms of psionic form factors, and is determined to be Delta Phi(Psi) = Phi(Psi)(E) - Phi(Psi)(M) = (71(-46)(+66) +/- 5)degrees. Similarly, the ratio between the form factors is found to be R-psi = vertical bar G(E)(Psi)/G(M)(Psi)vertical bar = 0.48(-0.35)(+0.21) +/- 0.03. The first uncertainties are statistical and the second systematic.

Automated summary

In this study, a measurement of A spin polarization in the e+e- -> Lambda(Lambda) over bar process at √s = 3.773 GeV is reported using a data sample of psi(3770) events collected with the BESIII detector at BEPCII. The phase between the transition amplitudes of the Lambda(Lambda) over bar helicity states is found to be zero, and the ratio between the form factors is determined.