The cos 2ϕ azimuthal asymmetry in ρ0 meson production in ultraperipheral heavy ion collisions

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.

Anisotropy in Dijet Production in Exclusive and Inclusive Processes

“…Our result in this paper will have a broad impact on the tomographic study of nucleons/nuclei at the future electron-ion collider (EIC) [52,53]. Various anisotropy observables have been proposed to study the novel structure of nucleon/nucleus [13][14][15][16][17][18][19][20][21][22]. The results in these previous works have to be re-examined.…”

“…Typically the two final state jets are produced in the socalled correlation configuration, namely, back-to-back in the transverse plane with nearly balanced transverse momenta [1][2][3][4][5][6][7][8]. Deviations from the perfect back-toback configuration inform important strong interaction physics, and, in particular, the non-perturbative structure of the nucleon and nucleus [9][10][11][12][13][14][15][16][17][18][19][20][21][22]. It is expected to reveal the medium property by studying de-correlation of dijet in heavy ion collisions as well [23][24][25][26][27][28][29][30].…”

Coulomb nuclear interference effect in dipion production in ultraperipheral heavy ion collisions

“…The resulting unpolarized cross section gives excellent description to the STAR experimental data. We further computed the cos 2φ azimuthal asymmetry induced by the linear polarization of photons, and are able to describe its q ⊥ dependent behavior reasonably well [29].…”

“…The observed asymmetries result from incident photon's linear polarization. Its unique diffractive pattern crucially depends on transverse spacial distribution of the gluonic matter inside nucleus, and double slit like quantum interference effect [29].…”

Azimuthal Angular Asymmetry of Soft Gluon Radiation in Jet Production

“…Another example is the inclusive dijet production in DIS, where q ⊥ comes from the intrinsic transverse momentum of gluons in the target. In this case, the so-called linearly polarized gluon distribution can generate a cos(2φ) asymmetry in the dijet system [18][19][20][21][22][23][24]. However, the momentum imbalance q ⊥ can simply come from perturbative initial and final state radiations which have nothing to do with nontrivial parton distributions inside the target.…”