Measurement of Λ transverse polarization in e + e − collisions at $\sqrt{s}$ = 3.68 − 3.71 GeV

With data samples collected with the BESIII detector at seven energy points at $\sqrt{s}$ = 3.68 − 3.71 GeV, corresponding to an integrated luminosity of 333 pb −1, we present a study of the Λ transverse polarization in the e + e − → $\Lambda \overline{\Lambda }$ reaction. The significance of polarization by combining the seven energy points is found to be 2.6σ including the systematic uncertainty, which implies a non-zero phase between the transition amplitudes of the $\Lambda \overline{\Lambda }$ helicity states. The modulus ratio and the relative phase of EM-psionic form factors combined with all energy points are measured to be R Ψ = ${0.71}_{-0.10}^{+0.10}$ ± 0.03 and ∆ΦΨ = ${23}_{-8.0}^{+8.8}$ ± 1.6°, where the first uncertainties are statistical and the second systematic.