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

TL;DR

This paper investigates how Coulomb and nuclear interactions interfere in dipion production during ultraperipheral heavy ion collisions, revealing azimuthal asymmetries that help understand the scattering amplitude phase.

Contribution

It demonstrates the significance of Coulomb nuclear interference effects on azimuthal asymmetries in dipion production, providing a new way to probe the dipole-nucleus scattering phase.

Findings

Coulomb nuclear interference causes sizable azimuthal asymmetries.

Azimuthal asymmetries can constrain the phase of dipole-nucleus scattering.

Interference effects are prominent at very low pair transverse momentum.

Abstract

We study exclusive $\pi^+ \pi^-$ pair production near $\rho^0$ resonance peak in ultraperipheral heavy ion collisions. Pion pair can either be produced via two photon fusion process or from the decay of $\rho^0$ in photon-nuclear reaction. At very low pair transverse momentum, the electromagnetic and nuclear amplitudes become comparable. We show that the Coulomb nuclear interference amplitude gives rise to sizable $\cos \phi$ and $\cos 3\phi$ azimuthal asymmetries, which can be used to constrain the phase of the dipole-nucleus scattering amplitude.