Speaker
Description
The longitudinal and transverse spin transfer to $\Lambda$ and $\overline{\Lambda}$ hyperons in polarized proton-proton collisions is expected to be sensitive to the helicity and transversity distributions of strange and anti-strange quarks of the proton, as well as the corresponding polarized fragmentation functions. In this talk, we will present the improved measurements of longitudinal spin transfer to $\Lambda$ and $\overline{\Lambda}$, $D_{LL}$, and transverse spin transfer to $\Lambda$ and $\overline{\Lambda}$, $D_{TT}$, in polarized proton-proton collisions at $\sqrt{s} = 200$ GeV with the STAR experiment at RHIC. The data set includes longitudinally and transversely polarized proton-proton collision samples with an integrated luminosity of 52 pb$^{-1}$ in each cases. Both data sets have about two times larger figure of merit than prior results and cover a kinematic range of $|\eta|$ $<$ 1.2 and transverse momentum $p_T$ up to 8 GeV/$c$. We also report first measurements of the hyperon spin transfer $D_{LL}$ and $D_{TT}$ versus fractional momentum $z$ of the hyperon within a jet, which can provide more direct constraints on the polarized fragmentation functions.
