Speaker
Description
The |t| dependence of coherent $\rho^0$ photoproduction probes the transverse structure of the interaction and exhibits diffractive dip structures related to saturation effects. Under s-channel helicity conservation, photon polarization is transferred to the vector meson, leading to a $\cos(2\phi)$ modulation of its decay distribution. Since either nucleus can emit the photon, the two indistinguishable production amplitudes can interfere, giving rise to a unique spin-interference pattern. In this talk the $|t|$-dependent differential cross section for coherent $\rho^0$ photoproduction will be presented in pPb and PbPb collisions. Furthermore a ZDC-dependent study of the $\cos(2\phi)$ modulation will be presented in the midrapidity region ($|y|<0.8$) where a significant modulation effect is expected. These measurements provide sensitivity to the impact-parameter dependence of the modulation strength, which increases with increasing neutron emission from the nuclei.