Which of the following physicists did NOT work on the Manhattan project?

Murray Gell-Mann did not work on the Manhattan Project because he was a theoretical physicist who primarily focused on the study of elementary particles and their interactions. While the Manhattan Project involved the development of atomic weapons during World War II, Gell-Mann's research and contributions were in the field of quantum mechanics and particle physics, particularly his work on the theory of quarks and the development of the Eightfold Way classification scheme. Therefore, his specialized area of study did not align with the goals and focus of the Manhattan Project.