Exclusive electroproduction of two pions at HERA

The exclusive electroproduction of two pions in the mass range 0.4<M ππ<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<Q 2<80 GeV 2, 32<W<180 GeV and {pipe}t{pipe}<0. 6 GeV 2, where Q 2 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, {pipe}F(M ππ){pipe}, 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 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 -.