Paper detail

Longitudinal and transverse spin transfer to $Λ$ and $\overlineΛ$ hyperons in polarized $p$+$p$ collisions at $\sqrt{s} = 200$ GeV

The longitudinal and transverse spin transfers to $Λ$ ($\overlineΛ$) hyperons in polarized proton-proton collisions are expected to be sensitive to the helicity and transversity distributions, respectively, of (anti-)strange quarks in the proton, and to the corresponding polarized fragmentation functions. We report improved measurements of the longitudinal spin transfer coefficient, $D_{LL}$, and the transverse spin transfer coefficient, $D_{TT}$, to $Λ$ and $\overlineΛ$ in polarized proton-proton collisions at $\sqrt{s}$ = 200 GeV by the STAR experiment at RHIC. The data set includes longitudinally polarized proton-proton collisions with an integrated luminosity of 52 pb$^{-1}$, and transversely polarized proton-proton collisions with a similar integrated luminosity. Both data sets have about twice the statistics of previous results and cover a kinematic range of $|η_{Λ(\overlineΛ)}|$ $<$ 1.2 and transverse momentum $p_{T,{Λ(\overlineΛ)}}$ up to 8 GeV/$c$. We also report the first measurements of the hyperon spin transfer coefficients $D_{LL}$ and $D_{TT}$ as a function of the fractional jet momentum $z$ carried by the hyperon, which can provide more direct constraints on the polarized fragmentation functions.