arXiv subjects
Publications and source records attributed to Ya-jin Zhou.
We investigate the impact parameter dependence of the $\cos 4ϕ$ azimuthal asymmetry for electromagnetic lepton pair production in heavy ion collisions. The asymmetry induced by linearly polarized coherent photons exhibits strong impact parameter dependence.
We propose to measure the linear polarization of the external electromagnetic fields of a relativistic heavy ion through azimuthal asymmetries in dilepton production in ultraperipheral collisions. The asymmetries estimated with the equivalent photon approximation are shown to be sizable.
We perform a phenomenological analysis of the $\cos 2 ϕ$ azimuthal asymmetry in virtual photon plus jet production induced by the linear polarization of gluons in unpolarized $pA$ collisions. Although the linearly polarized gluon distribution becomes maximal at small $x$, TMD evolutionleads to a Sudakov suppression of the asymmetry with increasing invariant mass of the $γ^*$-jet pair. Employing a small-$x$ model input distribution, the asymmetry is found to be strongly suppressed under TMD evolution, but still remains sufficiently large to be measurable in the typical kinematical region accessible at RHIC or LHC at moderate photon virtuality, whereas it is expected to be negligible in $Z/W$-jet pair production at LHC. We point out the optimal kinematics for RHIC and LHC studies, in order to expedite the first experimental studies of the linearly polarized gluon distribution through this process. We further argue that this is a particularly clean process to test the $k_t$-resummation formalism in the small-$x$ regime.
The longitudinal polarization of hyperons in $e^+e^-$ annihilation at high energies depends on the longitudinal polarization of the quark produced at the $e^+e^-$ annihilation vertex whereas the spin alignment of vector mesons is independent of it. They exhibit very different energy dependences. We use the longitudinal polarization of Lambda hyperon and the spin alignment of $K^*$ as examples and present numerical results of energy dependences. We present the results at the leading twist with perturbative QCD evolutions of fragmentation functions at the leading order.