Experimentally, the most precise measurement of the proton radius comes from the PSI experiment: R = 0.84184 (67) × 10-13 cm. [R. Pohl et al., "The size of the proton," Nature 466, 213 (2010).] This measurement is controversial, since it differs by 4% from the CODATA world average (R=0.8768 (69) x 10-13 cm). Putting the controversy aside, explain why the PSI experiment could get such impressive accuracy using muonic hydrogen (a muon- proton bound state) instead of ordinary hydrogen (an electron-proton bound state). [Hint: The muon is 206.8 times heavier than the electron.] Mark all of the following that are true: The Bohr radius for muonic hydrogen is much larger than in normal hydrogen The Bohr radius for muonic hydrogen is much smaller than in normal hydrogen The charge of a muon is much larger than the charge of an electron Muons and protons interact by forces other than electromagnetism, so the potential is qualitatively different Muonic hydrogen cannot form > 0 states Muonic hydrogen is much larger than normal hydrogen Muonic hydrogen is much smaller than normal hydrogen

Experimentally, the most precise measurement of the proton radius comes from the PSI experiment: R = 0.84184 (67) × 10-13 cm. [R. Pohl et al., "The size of the proton," Nature 466, 213 (2010).] This measurement is controversial, since it differs by 4% from the CODATA world average (R=0.8768 (69) x 10-13 cm). Putting the controversy aside, explain why the PSI experiment could get such impressive accuracy using muonic hydrogen (a muon- proton bound state) instead of ordinary hydrogen (an electron-proton bound state). [Hint: The muon is 206.8 times heavier than the electron.] Mark all of the following that are true: The Bohr radius for muonic hydrogen is much larger than in normal hydrogen The Bohr radius for muonic hydrogen is much smaller than in normal hydrogen The charge of a muon is much larger than the charge of an electron Muons and protons interact by forces other than electromagnetism, so the potential is qualitatively different Muonic hydrogen cannot form > 0 states Muonic hydrogen is much larger than normal hydrogen Muonic hydrogen is much smaller than normal hydrogen