The Proton Radius Puzzle as an Interface Effect Evidence for Reduced–Mass–Dependent Short–Range Physics

This paper addresses the proton radius puzzle by re-examining how the proton charge radius is operationally extracted from atomic spectroscopy. Rather than treating the radius as a system-independent property of the proton, the analysis shows that finite-size effects necessarily probe a reduced-mass–dependent short-range interaction region. Using only experimentally measured differences and dimensional scaling arguments, the work demonstrates that a single interface length resolves the discrepancy between electronic and muonic hydrogen without introducing new parameters or modifying quantum electrodynamics. Transfer tests to deuterium, muonic deuterium, and helium-3 are discussed. The results suggest that the proton radius puzzle may serve as a sensitive probe of underlying interface or geometric descriptions of short-range atomic physics.