Improved measurement of the longitudinal spin transfer to $\hat{I}›$ and $\bar{\hat{I}}›$ hyperons in polarized proton-proton collisions at $\sqrt{s}$ = 200 GeV

Abstract

The longitudinal spin transfer $D_{LL}$ to $\hat{I}›$ and $\bar{\hat{I}}›$ hyperons produced in high-energy polarized proton--proton collisions is expected to be sensitive to the helicity distribution functions of strange quarks and anti-quarks of the proton, and to longitudinally polarized fragmentation functions. We report an improved measurement of $D_{LL}$ from data obtained at a center-of-mass energy of $\sqrt{s}$ = 200 GeV with the STAR detector at RHIC. The data have an approximately twelve times larger figure-of-merit than prior results and cover $|\hat{I}\cdot |<$ 1.2 in pseudo-rapidity with transverse momenta $p_T$ up to 6 GeV/c. In the forward scattering hemisphere at largest $p_T$, the longitudinal spin transfer is found to be $D_{LL}$ = -0.036 $\pm$ 0.048 (stat) $\pm$ 0.013(sys) for $\hat{I}›$ hyperons and $D_{LL}$ = 0.032 $\pm$ 0.043\,(stat) $\pm$ 0.013\,(sys) for $\bar{\hat{I}}›$ anti-hyperons. The dependences on $\hat{I}\cdot$ and $p_T$ are presented and compared with model evaluations.

8 pages, 4 figures