<P> The radius is linked to the form factor and momentum transfer cross section . The atomic form factor G modifies the cross section corresponding to point - like proton . </P> <Dl> <Dd> R e 2 = − 6 d G e d q 2 q 2 = 0 d σ d Ω = d σ d Ω p o i n t G 2 (q 2) (\ displaystyle (\ begin (aligned) R_ (e) ^ (2) & = - 6 ((\ frac (dG_ (e)) (dq ^ (2))) \, (\ Bigg \ vert) \,) _ (q ^ (2) = 0) \ \ (\ frac (d \ sigma) (d \ Omega)) \ & = ((\ frac (d \ sigma) (d \ Omega)) \, (\ Bigg \ vert) \,) _ (point) G ^ (2) (q ^ (2)) \ end (aligned))) </Dd> </Dl> <Dd> R e 2 = − 6 d G e d q 2 q 2 = 0 d σ d Ω = d σ d Ω p o i n t G 2 (q 2) (\ displaystyle (\ begin (aligned) R_ (e) ^ (2) & = - 6 ((\ frac (dG_ (e)) (dq ^ (2))) \, (\ Bigg \ vert) \,) _ (q ^ (2) = 0) \ \ (\ frac (d \ sigma) (d \ Omega)) \ & = ((\ frac (d \ sigma) (d \ Omega)) \, (\ Bigg \ vert) \,) _ (point) G ^ (2) (q ^ (2)) \ end (aligned))) </Dd> <P> The atomic form factor is related to the wave function density of the target: </P>

Where does the mass of the proton come from