Probing the gluon tomography in photoproduction of dipion

A sizable cos 4 phi azimuthal asymmetry in exclusive dipion production near p degrees resonance peak in ultraperipheral heavy-ion collisions recently has been reported by STAR collaboration. We show that both elliptic gluon Wigner distribution and final-state soft photon radiation can give rise to this azimuthal asymmetry. The fact that the QED effect alone severely underestimates the observed asymmetry might signal the existence of the nontrivial correlation in quantum phase distribution of gluons.

Automated summary

In ultraperipheral heavy-ion collisions, a sizable cos 4 phi azimuthal asymmetry in exclusive dipion production near the p degrees resonance peak has been reported by the STAR collaboration. This asymmetry may be generated by both elliptic gluon Wigner distribution and final-state soft photon radiation. The observed asymmetry, underestimated by QED effects alone, may suggest nontrivial correlation in the quantum phase distribution of gluons.