Measurement of longitudinal spin transfer to the Λ-hyperon at HERMES

The spin transfer to the Λ-hyperon from a longitudinally polarized positron beam has been measured at the HERMES experiment in the semi-inclusive reaction e→+p(d)→e'+Λ→+X in deep inelastic scattering regime with negative four-momentum transfer squared of the exchanged virtual photon Q2>1GeV2. The data were accumulated in the years 1996-2000 using the 27.5 GeV polarized HERA positron beam and an unpolarized internal gas target in a storage cell. The longitudinal spin transfer coefficient DLL'Λ is found to be 0.11 ± 0.10(stat) ± 0.03(syst) at the average fractional Λ energy =0.45