meson

measured

meson mass

$m_{meas}$

calculated

meson mass

$m_{calc}$

$\frac{m_{calc}-m_{meas}}{m_{meas}}$

${\pi }^{\pm }$

$273.13m_e$

$2\frac{m_e}{\alpha }=274.1m_e$

$3.5\times {10}^{-3}$

${\mu }^{\pm }$

$206.77m_e$

$\frac{3}{2}\frac{m_e}{\alpha }=205.6m_e$

$-5.8\times {10}^{-3}$