We report our measurement on longitudinal spin transfer, D_LL, from high energy polarized protons to $Lambda$ and $bar{Lambda}$ hyperons in proton-proton collisions at $sqrt{s} = 200 GeV$ with the STAR detector at RHIC. The current measurements cover
$Lambda$, $barLambda$ pseudorapidity $|eta| < 1.2$ and transverse momenta $p_T$ up to $4GeV/c$ using the data taken in 2005. The longitudinal spin transfer is found to be D_LL= -0.03pm 0.13 (stat) pm 0.04(syst)$ for inclusive $Lambda$ and $D_{LL} = -0.12 pm 0.08(stat) pm 0.03(syst)$ for inclusive $bar{Lambda}$ hyperons with $<eta> = 0.5$ and $<p_T> = 3.7 GeV/c$. The prospects with 2009 data and the future measurements are also given.
We study the longitudinal polarization of hyperons and anti-hyperons at forward pseudorapidity, $2.5<eta<4$, in singly polarized $pp$ collisions at RHIC energies by using different parameterizations of the polarized parton densities and different mod
els for the polarized fragmentation functions. The results show that the $Sigma^+$ polarization is able to distinguish different pictures on spin transfer in high energy fragmentation processes; and the polarization of $Lambda$ and $barLambda$ hyperons can provide sensitivity to the helicity distribution of strange sea quarks. The influence from beam remnant to hyperon polarization in the forward region is also discussed.
