The project was motivated by the recent developments in the measurement of the 3D structures of the proton, made possible by theoretical developments on generalized parton distributions (GPD) and transverse momentum dependent parton distribution functions (TMD). While the application of these framework to the study of nuclei has been explored early on, the experimental access was long though to be impracticable, leaving the nuclear 3D structure completely unknown. However, a recent experimental breakthrough has open the possibility to perform these measurements with unique opportunities to explore the partonic structure of the nucleus in completely new ways.
Using the GPD framework, we can not only perform a 3D tomography, but also access the non-nucleonic degrees of freedom in the nucleus. The TMD framework on the other hand is sensitive to very different physics in the nuclei, providing a unique access to the nuclear structure in momentum space and, through it, to the gluon saturation scale. Moreover, these experimental developments triggered a renewed interest to measure reactions in which we detect the remnants of the nucleus at the same time as we detect high energy hadrons. Such experiments, on heavy nuclei are one of the best opportunity to understand the origin of the modification of the nuclear quark structure, the so called EMC effect.
To perform these experiments, we are building a new detector with an original design named ALERT (A Low Energy Recoil Tracker). This detector will measure the nuclear deeply virtual Compton scattering (DVCS) at a much higher luminosity than in the seminal experiment mentioned above. At the same time, its excellent capability to differentiate nuclear isotopes, will open the opportunity to measure the tagged reactions, in which we detect the remnants of the nucleus. The project will bring about this effort by addressing all the different experimental aspects of the field from the detector R&D to the phenomenology necessary to the interpretation of the data.
The goals of the project are (i) to perform independently the quark and the gluon tomography of the helium nucleus, (ii) to measure nuclear TMDs and the gluon saturation scale, (iii) to understand the correlations between the EMC effect and the internal nucleon motions in the nucleus, and (iv) to design and build the ALERT detector necessary to these experiments. These different goals form a coherent program to reset our understanding of the nucleus, from the standard few body system composed of protons and neutrons, to a fully QCD object defined in terms of quarks and gluons. In particular, this project will answer key questions of modern hadronic physics, namely: ”Are quarks and gluons distributions similarly modified in the nucleus?”, ”What is the gluon saturation scale and does it scale in nuclei as A1/3 ?”, and ”What is the origin of the EMC effect?”