The Non-Fundamental Nature of Proton Mass: Independent Derivation of 938.272 MeV from Energy Conservation

Proton mass m_p = 938.272 MeV/c² is treated as a fundamental input parameter in the Standard Model of particle physics, its value determined by experimental measurement, and its origin unquestioned by the theory. This paper demonstrates that the proton mass can be independently derived from energy conservation, without assuming any intrinsic property of the proton. The derivation uses only three known quantities: the free neutron rest mass, the electron energy spectrum endpoint value E_max = 0.782 MeV from free neutron β-decay, and the electron rest energy 0.511 MeV—which was independently derived from the atomic mass difference between deuterium and hydrogen-1 in a preceding paper. Through a single step of energy conservation, 938.272 MeV/c² is precisely obtained. The result shows that the proton mass is not an intrinsic property of the proton, but the energy retained by the sealed field after a neutron disintegration event. Together with the independent derivation of electron rest energy 0.511 MeV, this finding points to a systematic conclusion: multiple entries in the table of fundamental constants are not original settings of the universe, but derivable outcomes of deeper physical processes.