Abstract
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 compute the unpolarized cross section and cos 2ϕ azimuthal angular correlation for ρ0 photoproduction with ϕ defined as the angle between the ρ0’s transverse momentum and its decay product pion meson’s transverse momentum. Our result on unpolarized coherent differential cross section gives excellent description to the STAR experimental data. A first compari- son between theoretical calculation and experimental measurement on the cos 2ϕ azimuthal asymmetry, which results from the linearly polarized photons, is performed and reasonable agreement is reached. We find out the characteristic diffractive patterns at both RHIC and LHC energies and predict the impact parameter dependent cos 2ϕ azimuthal asymmetries for ρ0 photoproduction by considering UPCs and peripheral collisions. The future experimental measurements at RHIC and LHC relevant to our calculations will provide a tool to rigorously investigate the coherent and incoherent production of vector meson in UPCs, as well as to probe the nuclear structure in heavy ion collisions.
Highlights
We present a detailed study of vector meson photoproduction in ultraperipheral heavy ion collisions (UPCs)
We find out the characteristic diffractive patterns at both RHIC and LHC energies and predict the impact parameter dependent cos 2φ azimuthal asymmetries for ρ0 photoproduction by considering UPCs and peripheral collisions
We have studied the cos 2φ azimuthal angular correlation in vector meson production in ultraperipheral heavy ion collisions, where φ is defined as the angle between vector meson’s transverse spin vector and its transverse momentum
Summary
We consider vector meson ρ0 production in UPCs, A + A → ρ0 + A + A. As the convolution of the dipole scattering amplitude and the overlap between the vector meson and photon wave functions in position space, A(∆⊥) = i d2b⊥ei∆⊥·b⊥. The polarization dependent wave function Ψγ→qq (ΨV →qq) of the quasi-real photon (vector meson) is determined from light cone perturbation theory at leading order in the section below. By invoking the Ward identity argument, one can derive the same wave function with polarization vector −k⊥μ /x instead of P μ for a quasi-real photon that carries momentum xP μ + k⊥μ [32], where P μ is the four-momentum for the beam nucleus. (2.3) and (2.4), and summing over the color and helicities of the quark and antiquark, we obtain the overlaps between the photon and the vector meson wave functions, Ψγ→qqΨV →qq∗. As mentioned in the introduction, the coupling of the spin states is the consequence of the Eikonal approximation employed in our calculation
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