Tomography of ultrarelativistic nuclei with polarized photon-gluon collisions

A linearly polarized photon can be quantized from the Lorentz-boosted electromagnetic field of a nucleus trav-eling at ultrarelativistic speed. When two relativistic heavy nuclei pass one another at a distance of a few nuclear radii, the photon from one nucleus may interact through a virtual quark-antiquark pair with gluons from the other nucleus, forming a short-lived vector meson (e.g., p(0)). In this experiment, the polarization was used in diffractive photoproduction to observe a unique spin interference pattern in the angular distribution of p(0) -> pi(+)pi(-) decays. The observed interference is a result of an overlap of two wave functions at a distance an order of magnitude larger than the p(0) travel distance within its lifetime. The strong-interaction nuclear radii were extract-ed from these diffractive interactions and found to be 6.53 +/- 0.06 fm (Au-197) and 7.29 +/- 0.08 fm (U-238), larger than the nuclear charge radii. The observable is demonstrated to be sensitive to the nuclear geometry and quantum interference of nonidentical particles.

Automated summary

A linearly polarized photon can be emitted when a nucleus travels at ultrarelativistic speed. The interaction between photons and quarks or gluons from two passing nuclei can form vector mesons, which shows a spin interference pattern in the decay distribution. The experiment measures the diffractive photoproduction of p(0) to observe the interference, and extracts the nuclear radii from these interactions, which were found to be larger than the nuclear charge radii. This observable is sensitive to nuclear geometry and quantum interference of nonidentical particles.