Thèse de la Physique à Petit Nombre de Degrés de Liberté à la Cinématique des Collisions d'Antinoyaux à Haute Énergie H/F - Doctorat.Gouv.Fr

Établissement : Université Paris-Saclay GS Physique École doctorale : Particules, Hadrons, Énergie et Noyau : Instrumentation, Image, Cosmos et Simulation Laboratoire de recherche : Laboratoire de Physique des deux Infinis Irène Joliot-Curie Direction de la thèse : Guillaume HUPIN ORCID 0000000242857411 Début de la thèse : 2026-10-01 Date limite de candidature : 2026-08-31T23:59:59 Ce projet de thèse vise à développer une description ab initio , dite bottom-up, des interactions noyau-antinoyau à basse énergie afin de permettre une modélisation fiable des
signaux de rayons cosmiques pertinents pour la matière noire. Nous calculerons des observables de diffusion, des décalages et largeurs des niveaux atomiques, ainsi que des observables d'annihilation, avec comme axe principal les collisions deutéron-antideutéron, et des extensions vers des noyaux légers de la couche p. En distinguant l'annihilation séquentielle de l'annihilation simultanée et en propageant les incertitudes issues des interactions NN and NbarN, nous fournirons des entrées nucléaires validées pour les expériences (PUMA/ALICE) ainsi que pour des applications en astroparticules. Un résultat majeur visera à transférer ces contraintes microscopiques dans le code de modèle réactionnel INCL afin d'améliorer la description de l'annihilation de l'antideutéron et de permettre une transition vers les mécanismes réactionnels sur une large gamme d'énergies. Cette boucle théorie-simulation, à double sens, fournira les données nucléaires et les outils de modélisation nécessaires pour interpréter les futures recherches d'anti-noyaux dans les rayons cosmiques. Antimatter is among the costliest materials ever produced by mankind (~100 B$ per gram), yet only vanishingly small amounts of hadronic antimatter have been created worldwide-at most a few tens of nanograms of antiprotons in total. Even if completely annihilated, this corresponds only to energies on the order of a few megajoules: negligible from an engineering perspective, but priceless scientifically. Antiprotons and light antinuclei are routinely produced at TeV accelerator facilities and are also observed in cosmic rays reaching Earth. Because rare antinuclei in space could carry information about exotic production mechanisms-including, potentially, dark-matter annihilation or decay-their study has become a high-impact frontier connecting nuclear physics, astroparticle physics, and collider measurements[1, 2]. Interpreting present and future antinuclei searches, however, is limited by a lack of key nuclear input data: low-energy scattering, annihilation, and breakup processes of antinuclei on ordinary matter are difficult to measure directly, precisely because producing and manipulating antinuclei is so challenging. This motivates a complementary, theory-driven strategy. Our project adopts a bottom-up approach: we will establish a controlled, ab initio description of the simplest low-energy antimatter nuclear systems and collisions, identify the underlying many-body mechanisms of annihilation, and then propagate these constraints to transport and event-level modeling at the many-body and higher-energy scales. In doing so, we aim to both deepen our understanding of matter-antimatter interactions at the nuclear level and deliver validated inputs for the simulation tools used in astroparticle and collider applications. In the context of the PUMA experiment at CERN[3], which will use low-energy antiprotons to access the nuclear periphery of exotic nuclei, we have started to build a predictive, ab initio theory framework for nuclear antimatter probes of light and medium-light nuclei, delivering reaction and annihilation observables that (i) directly support PUMA and (ii) connect to complementary constraints from collider femtoscopy. We are now targeting antinucleon collisions with p-shell nuclei up to oxygen, providing benchmarked predictions for reactions and annihilation that are relevant both to PUMA measurements on unstable isotopes and to broader astroparticle and rare-process program where antinucleon-nucleus dynamics enters detector response and background modelling. In parallel, we will use accurate calculations together with emerging data to tighten constraints on the still poorly determined microscopic NNbar interaction, whose long-range structure is linked to meson-exchange physics but remains limited by sparse low-energy datasets. Antideuterons (dbar) as composite antimatter probes are a core extension of our research. Thus, the next step is to tackle the largely unexplored case of nuclei-antinuclei systems, i.e. both with an internal structure, starting with (anti)deuteron capture and annihilation on light targets. Unlike single antinucleons, antideuterons introduce qualitatively new physics-binding, breakup channels, and competing sequential versus correlated annihilation mechanisms-that must be treated consistently in a microscopic framework. This extension is both timely and testable: ALICE has shown that femtoscopic observables[4] and dedicated interaction measurements can already provide stringent constraints in the light-antimatter sector, including for antinuclei up to A ~ 3 and for low-energy strong-interaction parameters. From a theory standpoint, deuteron/antideuteron projectiles require a controlled description of the weak binding and continuum.
We will address this through systematic continuum discretization, convergence studies, and uncertainty quantification within our NCSM-based reaction framework, enabling the first consistent ab initio predictions for elastic and inelastic scattering, breakup, and annihilation of antideuterons on light nuclei. These results will provide validated inputs for (i) antimatter-nucleus program at CERN and (ii) astrophysical applications where antideuteron interactions in matter enter propagation and detector modeling. Research objectives for simulations: Antiproton-nucleus reactions, ranging from low-energy capture to a few GeV, are of significant interest for several reasons. From the perspective of the reaction itself, there is the question of whether the models used for conventional projectiles can accurately simulate the products that emerge (such as emitted particles and residual nuclei) regardless of energy and target nuclei[5]. Additionally, these reactions have important applications, such as studying the structure of exotic nuclei[3] ,Schupp2025and investigating dark matter[7]. For these reasons, the INCL (IntraNuclear Cascade of Liège) code has been developed to incorporate these reactions and has included antiproton-nucleus reactions since 2023[8]. The code has recently been extended to anti-neutrons, with a version included in Geant4[9]. Currently, a version with anti-deuterons is being validated. At low energy, anti-deuterons, similar to antiprotons and anti-neutrons, can be captured by the nucleus, cascade towards the nucleus, and be annihilated there. Key questions include the location of annihilation and the type of nucleon annihilated. While some information exists on both aspects, it is not as precise or complete as desired. For anti-deuterons, an additional question arises: does the anti-deuteron annihilate on a pair of nucleons, or does one of the antinucleons annihilate while the other enters the nucleus to undergo a later interaction (such as elastic scattering, annihilation, or charge exchange)? Although a choice has been made in the INCL code based on existing literature[10], a more precise understanding of the probability of full versus partial annihilation is needed. It is also worth noting that anti-He3 is a candidate for dark matter studies, and the ALICE collaboration has published effective cross-section measurements[11] that could be useful for this purpose. Therefore, once the case of the anti-deuteron is properly addressed in the INCL code, the next logical step will be to include anti-He3.

Le candidat doit être titulaire d'un diplôme équivalent à un master en physique subatomique/quantique/matière condensée. Le poste requiert de solides connaissances en physique théorique, en informatique et en calcul haute performance (HPC), un haut niveau de communication, à la fois orale et écrite (anglais requis, des cours de français sont dispensés aux candidats étrangers) pour être en mesure de présenter des conférences et de rédiger des articles scientifiques à publier dans des revues à comité de lecture. Nous recherchons un doctorant capable de s'impliquer pleinement dans le projet, désireux d'apprendre, doté d'une certaine indépendance de pensée et d'une forte motivation pour développer des compétences en recherche ainsi que les compétences techniques requises en informatique/HPC, etc. En outre, le candidat doit être capable de travailler en équipe.