Exclusive electroproduction of two pions at HERA

The exclusive electroproduction of two pions in the mass range 0.4< Mππ <2.5 GeV has been studied with the ZEUS detector at HERA using an integrated luminosity of 82 pb-1. The analysis was carried out in the kinematic range of 2< Q2<80 GeV2, 32<W<180 GeV and vertical stroke t vertical stroke <0.6 GeV2, where Q2 is the photon virtuality, W is the photon-proton centre-of-mass energy and t is the squared four-momentum transfer at the proton vertex. The two-pion invariant-mass distribution is interpreted in terms of the pion electromagnetic form factor, vertical stroke F(Mππ) vertical stroke, assuming that the studied mass range includes the contributions of the ρ, ρ' and ρ'' vector-meson states. The masses and widths of the resonances were obtained and the Q2 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-. (orig.)