PhD in Physics – Accessing the Pion 3D Structure with CLAS12

The understanding of the origin of the mass, the spin and the structure of the hadrons (protons, pions,…) from their elementary constituents (quarks and gluons, collectively called partons) is among the unanswered questions in particle physics. The theoretical framework of the Generalized Parton Distributions (GPDs) encodes the 3-dimensional structure of a hadron and its study provides insights on the origin of these fundamental properties. Experimentally, the cleanest method to study the internal structure of hadrons is to collide them with electrons at high energies. Staff at the Institute of Research into the Fundamental Laws of the Universe (IRFU) who are based in the Commissariat à l’Énergie Atomique (CEA) de Saclay (France), as well as staff in the Nuclear and Hadron Physics (NHP) Research Group at the University of Glasgow, 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 JLab allows the study of the properties of the hadrons via rare processes.

Being a “simple” bound state formed by a quark-antiquark pair, the pion is associated to the most advanced theoretical predictions derived from the first principles of quantum chromodynamics, including GPDs. Confronting these predictions to experimental data would allow a breakthrough in the understanding of the strong interaction, especially since the pion holds the very peculiar feature of being a Nambu-Goldstone boson. Unfortunately the experimental data on pions are quite scarce. The CLAS12 spectrometer based at JLab offers a unique opportunity to enrich this dataset. Indeed the proton is surrounded by a pion cloud, quark-antiquark pairs carrying the same quantum numbers as a pion. Electrons from the beam scatters sometimes on these pions, probing their structure. The high luminosity and the large acceptance of the CLAS12 particle detection system allows to study the deeply virtual Compton scattering (DVCS) on the pions of the meson cloud, a rare process providing access to their 3D structure.

The goal of this thesis will be to analyze the data taken with the CLAS12 experiment at the Jefferson Lab to extract the DVCS beam-spin asymmetry for pions. Given the large size of the datasets, the student will have the opportunity to develop and apply machine learning algorithms. A major source of systematic uncertainties arises from modelling the limitations of the particle detection reconstruction for the background processes. To reduce these systematics, we are going to investigate the use of conditional Generative Adversarial Network in order to create a “digital twin” of the Monte-Carlo/reconstruction chain with resolutions closer to experimental data, therefore more accurate than the ideal simulation and significantly faster.

The thesis will be carried out jointly between the NHP Research Group at the University of Glasgow and the Laboratory of Nucleon Structure of the Department of Nuclear Physics of CEA/Irfu. The CEA laboratory is composed of both experimentalists and theorists. The CEA laboratory is also closely working with the Department of detectors and IT for Physics at Irfu. These environments will offer many opportunities to the successful applicant.

Knowledge of particle physics and computer science would help the candidate to quickly and actively participate to the data analysis effort. Basics knowledge of particle detectors would be also an advantage to efficiently understand the experimental setup used for data collection. The student will also have the opportunity to collaborate with several researchers both locally in the University of Glasgow and local to CEA in France (like IJCLab in Orsay and CPHT at Ecole Polytechnique) and further internationally. The student will be part of the CLAS collaboration that will require frequent trips to the United States for data taking and workshops. The student will have the opportunity to present the results of these research topics to international conferences.

How to Apply: Please refer to the following website for details on how to apply: http://www.gla.ac.uk/research/opportunities/howtoapplyforaresearchdegree/.