Longitudinal and transverse spin transfer to $\hat{I}›$ and $\overline{\hat{I}}›$ hyperons in polarized $p$+$p$ collisions at $\sqrt{s}=200$ GeV

Abstract

The longitudinal and transverse spin transfers to $\hat{I}›$ ($\overline{\hat{I}}›$) 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 $\hat{I}›$ and $\overline{\hat{I}}›$ 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 $|\hat{I}{\cdot }_{\hat{I}›(\overline{\hat{I}}›)}|$ $<$ 1.2 and transverse momentum $p_{T,\hat{I}›(\overline{\hat{I}}›)}$ 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.