Spin transfer to $\Lambda_{c}^{+}$ hyperons in polarized proton   collisions at RHIC
  The analysis\cite{ohkuma:1} of helicity transfer to $\Lambda_{c}^{+}$ in polarized proton collisions is extended to the proton helicity correlations with the $\Lambda_{c}^{+}$ transverse polarization in the production plane (parameter $D_{LS}$). The available spin transfer observables for the collisions of {\em two} longitudinally polarized protons are evaluated. It is shown that, in the central region at $\Lambda_{c}^{+}$ transverse momenta of a few GeV/c, $D_{LS}$ parameters are of about the same size as the helicity-to-helicity correlations. The methodical issue of using spin transfers for cross-checks of systematic errors in cross-section $A_{LL}$ measurements at polarized proton colliders is also briefly discussed. 
V. L. Rykov and K. Sudoh