Division of Electronics, Detectors and Computing for Physics (DEDIP)

Hadronic matter is composed of fundamental particles called partons (quarks and gluons) and their interactions are described by Quantum Chromodynamics (QCD). Understanding and describing hadronic internal structure is one of the key challenges of nuclear physics. Despite a good description of the dynamics of quarks and gluons at high energy, several elementary hadronic properties (such as mass and spin) cannot be explained through their components with QCD calculations. Phenomenological approaches are therefore required as a theoretical framework to interpret experimental observations. These are the Generalized Parton Distributions (GPDs) and Transverse Momentum distributions (TMDs). These functions offer a 3D description of the nucleon as they give access to the spatial and momentum distributions of quarks and gluons and to parton contribution to the spin of the nucleon.

These distributions are experimentally accessible through electron scattering off proton and neutron (at the CEBAF accelerator in Jefferson Laboratory and the COMPASS experiment at CERN). One can also study it in polarized proton collisions with the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory.

The new detector sPHENIX is being assembled at RHIC and first collisions are scheduled for Spring 2023. About 350 researchers work around this 1000-ton apparatus. The physics program aims at understanding matter and the strong interaction. It covers both heavy-ion physics and matter deconfinement and the study of nucleon internal structure. Data taking will take place between 2023 and 2025 with pp, p-Au and Au-Au collisions at vsnn=200GeV.

The student will be involved in data taking and data analysis of the sPHENIX experiment. The main goal is the study of transverse momentum distributions of partons inside the proton. These results will contribute to deepen our understanding of nucleon structure and parton confinement.



In 2030 a new collider will be operational at RHIC: the electron-ion collider (EIC). The facility should give answers some of the most fundamental questions in nuclear physics. It will give access to a largely unexplored area: the limit of saturation for gluon density and will provide remarkable conditions to study the structure of the nucleon and the effect of a nuclear environment on the dynamics of quarks and gluons.

The CEA is involved in physics simulations and the development of innovative gaseous detectors. Part of the thesis will be dedicated to the study of several prototypes.



The thesis will be hosted by the Laboratory of the Nucleon Structure (Laboratoire de Structure du Nucleon, LSN) composed of several physicists, both some theoreticians and some experimentalists.



The student is expected to be fluent in English to work in the context of a large international scientific collaboration. He/she will have to show interest in detector hardware and software programming (C++).

Several trips should be anticipated, in particular to the United States.

CEA/Irfu staff members are among the principal investigators of ongoing experiments at the Jefferson Lab (JLab) in USA, where a high current electron beam up to 11 GeV in energy collides with fixed targets of several types. The high luminosity available at the JLab allows the study of the properties of the nucleons with high statistical accuracy also via rare processes.

Contrary to the naive expectations, it has been shown that not the valence quarks, but rather the gluons carry the major contribution to the mass and the spin of the nucleons. Therefore, it is crucial to precisely characterize gluons distributions in order to fully understand the strong interactions from which results the protons. In particular, the current knowledge of the GPDs of gluons is rather limited. GPDs are accessible through the study of exclusive processes where all the final state particles are detected, and specifically, gluon GPDs can be accessed via the study of the exclusive electroproduction of the ?-meson. This year, data are being collected with a longitudinally polarized target of protons, providing a unique opportunity to understand the correlation between the spin of the proton and the gluons. The goal of this thesis will be to analyze the data taken with the CLAS12 experiment at the Jefferson Lab to extract target-spin, beam-spin and double-spin asymmetries. The future PhD student will have the opportunity to add a side activity to the data analysis, the choice spanning from detector development to detailed phenomenological studies.