New method could explore gluon saturation in future electron-ion colliders

The U.S. nuclear physics community is preparing to build the Electron-Ion Collider (EIC), a flagship facility for probing the properties of matter and the strong nuclear force that holds it together. The EIC will allow scientists to study how nucleons (protons and neutrons) arise from the complex interactions of quarks and gluons.

A project led by researchers at Lawrence Berkeley National Laboratory demonstrates an important detector for studying gluon saturation in future EICs. Gluon saturation is the highest energy phenomenon within an atomic nucleus, when the production of gluons and their recombination are balanced, causing the gluon density to no longer depend on the collision energy.

The project shows that the nucleon energy-energy correlation (NEEC) provides different predictions from theories encoding high-density gluon saturation. Therefore, NEEC measurements will provide a good opportunity to determine the occurrence of gluon saturation phenomena in EIC electron-nucleus collisions.

The project resulted in two studies, one of which was published in Physical Review Letters Another one is in Physical Review D.

The NEEC probe has an advantage over other standard high-energy processes because it is fully inclusive. This makes the observable results theoretically and experimentally clean.

The researchers also showed that linearly polarized gluons confined inside unpolarized nuclei can be analyzed through additional energy correlations. The interference of gluons rotating in opposite directions translates into an asymmetry in the count rates observed in the detector. This provides a glimpse into the exquisite characterization of linearly polarized gluons and the associated nuclear tomography.

This will lead to an integrated approach to studying the universal behavior of gluon saturation. It will also complement future EIC research on other high-energy processes.