Gluons, together with quarks, are the fundamental constituents of the proton. They generate almost all its mass, carry about half of its momentum and contribute to its spin in a still unconstrained amount. Mapping their three-dimensional (3D) structure in the proton is crucial in our understanding of Quantum Chromodynamics and matter in general. The quark and gluon 3D content in momentum space is encoded in the so-called Transverse-Momentum-Dependent distribution/fragmentation functions (TMDs). While a huge progress had been made recently in the quark sector, the gluon sector was much less developed, due to the difficulty to cleanly probe gluons in high-energy processes. A very promising and also challenging way to access them is through quarkonium production (bound states of a quark-anti quark pair) in high-energy colliders. However, there was no solid framework which connected gluon TMDs to these processes.
The main goal of this project was to provide this new theoretical framework to properly access (un)polarized gluon TMDs through quarkonium production, also in view of the construction of new experimental facilities in Europe and the United States in the next decade, with the aim of collecting a wealth of data useful for gluon mapping.
This project brought new insights into our quest, as a society, of understanding the fundamental structure of matter. The same way as 3D imaging turned out to be revolutionary in many different ways for the man-kind, from medicine to location apps, the 3D mapping of nucleon structure will for sure have a tremendous impact in the future.
