Measurement of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi mathvariant="normal">Λ</mml:mi></mml:math> baryon polarization in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msup><mml:mi>e</mml:mi><mml:mo>+</mml:mo></mml:msup><mml:msup><mml:mi>e</mml:mi><mml:mo>−</mml:mo></mml:msup><mml:mo stretchy="false">→</mml:mo><mml:mi mathvariant="normal">Λ</mml:mi><mml:mover accent="true"><mml:mi mathvariant="normal">Λ</mml:mi><mml:mo …

Using a data sample of $\psi(3770)$ events collected with the BESIII detector at BEPCII corresponding to an integrated luminosity 2.9 fb$^{-1}$, we report measurement $\Lambda$ spin polarization in $e^+e^-\rightarrow\Lambda\bar\Lambda$ $\sqrt{s} = 3.773$ GeV. The significance is found be 2$\sigma$ including systematic uncertainty, which implies zero phase between transition amplitudes $\Lambda\bar{\Lambda}$ helicity states. This can interpreted terms psionic form factors, and determined $\Delta\Phi^{\Psi}$ $\Phi^{\Psi}_{E} - \Phi^{\Psi}_{M}$ $(71^{+66}_{-46}$ $\pm$ 5)$^{\circ}$. Similarly, ratio factors $R^{\psi}$ $|G^{\Psi}_{E}/G^{\Psi}_{M}|$ $0.48^{+0.12}_{-0.07}$ 0.04. first uncertainties are statistical second systematic.