Related papers: Rescattering effects on spin-interference for $\rh…
We report the first evidence of spin interference in exclusive $J/\psi \to e^+e^-$ photoproduction in ultraperipheral Au+Au and isobar (Ru+Ru, Zr+Zr) collisions ($\sqrt{s_{NN}} = 200$~GeV) at STAR. A negative $\cos(2\phi)$ modulation is…
Spin alignment of vector mesons in heavy-ion collisions provides a novel probe of quark polarization and hadronization mechanism in quark-gluon plasma. Hadronic rescattering may affect the measured spin alignment of vector mesons due to…
Spin alignments of vector mesons and hyperons in relativistic heavy-ion collisions have been proposed as signals of the global polarization. The STAR experiment first observed the $\rm \Lambda$ polarization. Recently, the ALICE…
We present recent STAR results on photoproduction in ultra-peripheral relativistic heavy ion collisions. In these collisions the impact parameter of the beam particles is larger than the sum of their nuclear radii, so that they interact via…
The diffractive $\phi$-meson photoproduction amplitude is dominated by the Pomeron exchange process and contains the terms that govern the spin-spin and spin-orbital interactions. We show that these terms are responsible for the spin-flip…
The strong electromagnetic fields of short duration associated with relativistic heavy ions make a heavy-ion collider a unique tool to study two-photon and photonuclear collisions. In this talk, we introduce the principles of…
Measurements of global spin alignment of vector mesons in relativistic heavy-ion collisions can provide unique insights into spin-orbit interactions and vector meson dynamics in the Quark-Gluon Plasma (QGP) produced in those collisions. The…
We present a detailed study of vector meson photoproduction in ultraperipheral heavy ion collisions (UPCs). Using the dipole model, we develop a framework for the joint impact parameter and transverse momentum dependent cross sections. We…
We present a summary of recent photoproduction results in ultra peripheral relativistic heavy ions collisions with STAR. These collisions have impact parameters larger then twice the nuclear radius; the nuclei do not physically collide, but…
Incoherent photoproduction of pions on the deuteron in the Delta(1232) resonance region is investigated in order to study the influence of final state NN and PiN rescattering. For the elementary production operator an effective Lagrangian…
We consider the role of hadronic rescattering of daughter kaons on the observed mass spectra from $\phi$ meson decays in ultra-relativistic heavy ion collisions. A hadronic cascade code (RQMD v2.4) shows that $\sim$26% of all $\phi$'s…
In ultra-peripheral relativistic heavy ion collisions the beam ions scatter at impact parameters larger than the sum of their radii, so that they interact via long range electromagnetic forces. Due to the Lorentz-boost of the beam…
We study, for the first time, differential distributions for two $\rho^0$ meson production in exclusive ultraperipheral, ultrarelativistic heavy ion collisions via a double-scattering mechanism. The calculations are done in the impact…
Significant enhancements of J/$\psi$ production have been observed by various experiments at RHIC and LHC for very low transverse momenta in peripheral heavy-ion collisions, which has ignited a surge of investigations into photon-induced…
Hadronic resonances are unique tools to investigate the interplay of re-scattering and regeneration effects during the hadronization phase in heavy-ion collisions. Measurements in small collision systems provide a necessary baseline for…
The resonance effects are investigated in the $\phi$ meson photoproduction near threshold through a quark model approach with an effective Lagrangian. The diffractive contribution is consistently estimated by the {\it t}-channel Pomeron…
Incoherent pion photoproduction on the deuteron is studied for photon energies from threshold up to 1 GeV with special emphasis on polarization observables. The elementary $\gamma N\to\pi N$ amplitude is taken from the MAID model. The…
We have investigated the $\rho^{0}$ meson photoproduction in ultraperipheral isobaric collisions between $_{44}^{96}\textrm{Ru}+_{44}^{96}\textrm{Ru}$ and $_{40}^{96}\textrm{Zr}+_{40}^{96}\textrm{Zr}$ at $\sqrt{s_{NN}}=200$ GeV, employing…
We report on our recent investigations in photonuclear production of heavy quarks and vector meson in ultraperipheral heavy ion collisions. In particular, our theoretical predictions are compared with the recent experimental measurements on…
We report a measurement of the Drell-S\"oding $\pi^+ \pi^-$ production in Au + Au ultraperipheral collisions at a center-of-mass energy per nucleon pair $\sqrt{s_{NN}} = 200~\mathrm{GeV}$ using the STAR detector. For the first time, the…