Ratio

Value

$\frac{\text{pionmass}}{\text{electronmass}}$

$0.9966\frac{4}{2\alpha }$

$\frac{\text{muonmass}}{\text{electronmass}}$

$1.0022\frac{3}{2\alpha }$

$\frac{\text{outershellmass}}{\text{electronmass}}$

$\frac{3}{2\alpha }$

$\frac{\text{zero-spinoutershellmass}}{\text{electronmass}}$

$\frac{2}{2\alpha }$

$\frac{\text{spinmass}}{\text{electronmass}}$

$\frac{2}{2\alpha }$