Measurement of Λ transverse polarization in e + e − collisions at √s = 3.68 − 3.71 GeV

With data samples collected with the BESIII detector at seven energy points at 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 − → Λ Λ ¯ 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 Λ Λ ¯ 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. [Figure not available: see fulltext.]