Exclusive vector meson production

The production of ground state vector mesons, V = ρ, ω, φ, J/ψ,Y, has been extensively studied at ep collider. Latest results were obtained from the study of two pion exclusive electroproduction in the mass range 0.4 < M_ππ < 2.5 GeV using 82 pb^-1 of integrated luminosity collected during 1998 - 2000 on ep collider with center-of-mass energy 318 GeV. The analysis was carried out in the kinematic range of 2 < Q² < 80 GeV², 32 < W < 180 GeV and |t| < 0.6 GeV². The two-pion invariant mass distribution is interpreted in terms of the pion electromagnetic form factor, |F(M _ππ)|, assuming that the studied mass range includes the contributions of the ρ, ρ′ and ρ″ vector meson states. The masses and widths of resonances are obtained and subsequently the Q ² dependence of the cross-section ratios σ(ρ′ → ππ)/σ(ρ) and σ(ρ″ → ππ)/ σ(ρ) was extracted. The pion form factor obtained in the present analysis is compared to that obtained in e⁺e^- → π⁺π^-.