Proton radius puzzle

The "proton radius puzzle" refers to a discrepancy in the measured size of the proton, a fundamental particle found in atomic nuclei. Traditionally, the proton radius has been measured using different experimental techniques, leading to conflicting results. 1. **Electron-Proton Scattering**: Historically, the radius of the proton was determined through experiments involving scattering electrons off protons. This method yielded a value of approximately 0.8768 femtometers (fm).