The radius of the rho meson determined from its decay constant

Abstract

We present a unified model describing electroweak properties of the pi and rho mesons. Using a general method of relativistic parametrization of matrix elements of local operators, adjusted for the nondiagonal in total angular momentum case, we calculate the rho-meson lepton-decay constant f_rho using the same parameters of free constituent quarks that have ensured exclusively good results for the pi meson previously. The only free parameter, characterizing quark interactions, which include additional spin-spin contribution and hence differ from the $\pi$-meson case, is fixed by matching the decay constant to its experimental value. The mean square charge radius is calculated, <r^2_rho>=(0.56+-0.04) fm^2. This result verifies, for the rho-meson case, the conjecture of equality between electromagnetic and strong radii of hadrons tested previously for proton, pi and K mesons.