Wave Functions and Form Factors for Relativistic Composite Particles. I

We give a relativistic description of composite particles which behave as nonrelativistic clusters in their rest frames. We find that the relativistic form factor can be obtained from the nonrelativistic one by the substitution $S\left(t\right)={\alpha }^{\frac{\mathrm{}(1-n)\mathrm{}}{2}}{S}_0\left(\frac{\mathrm{}\left|t\right|\mathrm{}}{\alpha }\right)$, where $\alpha =\frac{1-t}{\left(4\mathrm{}{M}_{A^2}\right)}$, and where $n$ is the number of subparticles in the cluster. An excellent one-parameter fit to the magnetic form factor of the proton is found.