PhD Position in Theoretical Particle Physics: quark-gluon tomography of nuclei at high energy

Job description: 3-years PhD at Subatech (France, Nantes) starting fall 2026 Quark-gluon tomography of nuclei at high energy Keywords: high energy particle physics, strong interaction, quantum chromodynamics, small x physics Scientific context and motivations This PhD project tackles some of the most fundamental open questions in our understanding of the strong interaction, one of the four fundamental forces of Nature. The strong force governs phenomena across a vast range of scales —from the binding of atomic nuclei at low energies to the intricate internal structure of protons and nuclei explored in high-energy collisions at major facilities such as the Large Hadron Collider (LHC) and the Relativistic Heavy Ion Collider (RHIC). At short distances, the strong interaction is described by Quantum Chromodynamics (QCD), the theory of quarks and gluons — collectively known as partons — which combine to form hadrons. Despite its remarkable success, QCD still presents profound theoretical challenges. This project focuses on two closely intertwined questions at the forefront of modern research: how partons are distributed inside hadrons, and the emergence of gluon saturation at high energies. A central goal of the project is to build a three-dimensional picture of hadron structure, encoding both the longitudinal momentum and transverse motion of quarks and gluons. This information is captured by Transverse Momentum Dependent (TMD) parton distribution functions. While parton tomography is essential for understanding how hadrons acquire their mass and spin, the behavior of TMDs in the small longitudinal momentum fraction (low-x) regime remains largely unexplored. Since first-principles lattice QCD approaches are currently unable to access this region, progress relies on high-precision perturbative QCD calculations combined with experimental data. However, beyond leading-order accuracy, such studies are still in their infancy at low x. In parallel, the project addresses gluon saturation, a striking phenomenon expected to arise at very high collision energies. In this regime, hadrons are dominated by a dense system of low-x gluons, where nonlinear recombination effects tame the growth of gluon densities and ensure consistency with fundamental unitarity constraints. This highly occupied gluonic matter is described by the Colour Glass Condensate (CGC), an effective field theory of QCD in the presence of strong gluon fields. Although theoretically compelling, gluon saturation has yet to be unambiguously established experimentally, and its quantitative features remain poorly constrained. The objective of this PhD project is to perform next-to-leading order (NLO) calculations within the CGC framework for a set of key processes whose cross sections can be factorized in terms of gluon and (sea) quark TMD distributions. These observables are directly relevant to current and future experiments at the LHC, including forward particle production in proton-nucleus (pA) collisions, a flagship physics program of LHCb and the future ALICE upgrade with the FoCal detector. Representative processes include forward photon-jet correlations, as well as inclusive and diffractive dijet or heavy-meson production in ultra-peripheral collisions. In addition, the project will involve the development of a dedicated numerical code to implement these calculations and perform detailed phenomenological studies. The ultimate goal is to identify clear and robust signatures of gluon saturation through the extraction of gluon and quark TMD distributions from experimental observables. The candidate We are primarily looking for students with a master degree in theoretical physics, educated on different aspects of high energy particle physics and QCD and having already acquired a basic knowledge in numerical physics. In addition to disciplinary knowledge mentioned above, the expected soft skills we expect from the candidate are: ability to carry out long and complex tasks by implementing control processes, spirit of initiative, imagination and curiosity. The PhD advisors and the local context The PhD will be performed under the joined supervision of Paul Caucal (caucal@subatech.in2p3.fr) and François Arleo (francois.arleo@subatech.in2p3.fr) who can be contacted for further information and questions on the application process. The PhD will take place inside the theory group of Subatech (presently 11 permanent researchers, 4 post docs, 3 PhD students). Subatech is a joint research unit comprising 3 research organizations: CNRS-IN2P3, IMT-Atlantique and Nantes Université. The 3-years position will be financed by Nantes Université through the Agence Nationale de la recherche (ANR) and attached to the 3MG graduate school. The recruitment process The recruitment process will run from mi-April 2026 until a suitable candidate has been found. First interviews are expected early June. Application files must be submitted on the following website : https://amethis.doctorat.org/amethis-client/prd/consulter/offre/2864 where further information on the PhD project can also be found. The application file should at least contain the following documents : A Curriculum Vitae, a cover letter outlining your professional project in relation with the PhD subject, transcripts of grades from “Bac+3” to “Bac+5” or equivalent (for results from a Master’s degree or equivalent, please attach any documents in your possession), at least 1 letter of reference from the master’s internship tutor. The application can be completed with any document considered relevant by the candidate Contact: Caucal, Paul (caucal@subatech.in2p3.fr); Arleo, François (francois.arleo@subatech.in2p3.fr) Letters of Reference should be sent to: https://amethis.doctorat.org/amethis-client/prd/consulter/offre/2864 More Information: https://amethis.doctorat.org/amethis-client/prd/consulter/offre/2864