## Abstract

A classification of particles is suggested based on a U(12) symmetry scheme. This is a relativistic generalization of the U(6) symmetry. The spin $\frac{1}{2}$ and $\frac{3}{2}$ baryons are each described by 20-component spinors which satisfy Bargmann-Wigner equations and belong to the 364 representation of the U(12) group while the vector and p.s. mesons belong to the representation 143. The procedure for writing fully relativistic form factors is worked out in detail for baryon-meson and meson-meson cases. The new results are the following: \begin{equation*}\tag{1}\frac{F^C(q^2)}{F^M(q^2)}\propto 1+\frac{q^2}{\langle2\mu\ranglem},\end{equation*} where F$^C$ and F$^M$ are (Sachs) electromagnetic form factors. \begin{equation*}\tag{2}\mu_p = 1 + 2m/\langle\mu\rangle,\end{equation*} where $\langle\mu\rangle$ is the mean mass of the 1-multiplet and m the nucleon mass. \begin{equation*}\tag{3}\mu_{\rho,\kappa*} = 3.\end{equation*} The conventional U(6) results can be recovered by projecting to the positive energy subspace in the rest system for each particle. To any irreducible representation of the U(6) there corresponds one irreducible representation of U(12) and vice versa.