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We study the longitudinal polarization of the Sigma_bar and Xi_bar anti-hyperons in polarized high energy pp collisions at large transverse momenta, extending a recent study for the Lambda_bar anti-hyperon. We make predictions by using different parametrizations of the polarized parton densities and models for the polarized fragmentation functions. Similar to the Lambda_bar polarization, the Xi_bar0 and Xi_bar+ polarizations are found to be sensitive to the polarized anti-strange sea in the nucleon. The Sigma_bar- and Sigma_bar+ polarizations show sensitivity to the light sea quark polarizations, Delta bar u(x) and Delta bar d(x), and their asymmetry.
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We argue that the enhancement in the spin polarization of anti-hyperons compared to the polarization of the hyperons in noncentral relativistic heavy-ion collisions arises as a result of an interplay between the chiral and helical vortical effects. The chiral vortical effect generates the axial current of quarks along the vorticity axis while the recently found helical vortical effect generates the helicity flow -- the projection of the quarks polarization vector onto its momentum -- along the same axis. For massless fermions, the helical charge corresponds to a difference in the contributions of particles and anti-particles to the axial charge. Assuming that the spin of light quarks transfers to the strange quarks via the vector kaon states (the spin-vector dominance), we are able to describe the ratio of the (anti)hyperon spin polarizations, obtained by the STAR group, without fitting parameters. We also argue that the helical vortical effect dominates over the chiral vortical effect and the chiral magnetic effect in the generation of the electric current.
We study the longitudinal polarization of hyperons and anti-hyperons at forward pseudorapidity, $2.5<eta<4$, in singly polarized $pp$ collisions at RHIC energies by using different parameterizations of the polarized parton densities and different models for the polarized fragmentation functions. The results show that the $Sigma^+$ polarization is able to distinguish different pictures on spin transfer in high energy fragmentation processes; and the polarization of $Lambda$ and $barLambda$ hyperons can provide sensitivity to the helicity distribution of strange sea quarks. The influence from beam remnant to hyperon polarization in the forward region is also discussed.
We discuss the relation between the polarization of inclusively produced (anti)-hyperons and the incident baryon states in the framework of the constituent quark-diquark cascade model. We assume that there is an intrinsic diquark-antidiquark state in the incident baryon, in which the intrinsic diquark immediately fragments into a non-leading baryon and the antidiquark behaves as a valence constituent. It is also assumed that the valence (anti)diquark in the incident nucleon tends to combine selectively with a spin-down sea quark and, on the othe hand, the spin-up valence quark in the projectile is chosen by a sea (anti)diquadk in preference to the spin-down valence quark. It is found that the incident spin-1/2 baryon is mainly composed of a spin-0 valence diquark and a valence quark, and contains an intrinsic diquark-antidiquark state with a probability of about 7%.
We discussed the photoproduction of pair of charged particles $abar{a}quad (a=e,mu,pi)$ as well as the double photon emission processes off an electron accounting for the polarization of colliding particles. In the kinematics when all the particles can be considered as a massless, we obtain the compact analytical expressions for the differential cross sections of these processes. As the application of obtained results the special cases of production by circular and linear polarized photons are considered.
We calculate the cross section and single-spin azimuthal asymmetry, A_n(t) for inclusive neutron production in pp collisions at forward rapidities relative to the polarized proton. Absorptive corrections to the pion pole generate a relative phase between the spin-flip and non-flip amplitudes, which leads to an appreciable spin asymmetry. However, the asymmetry observed recently in the PHENIX experiment at RHIC at very small |t|~0.01GeV^2 cannot be explained by this mechanism.
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