Dr Justyna Tomaszewska (DESY)
The exclusive electroproduction of two pions in the mass range 0.4 < M(pipi) < 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 |t|<0.6 GeV, 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, |F(M(pipi)|, assuming that the studied mass range includes the contributions of the rho, rho' and rho'' vector-meson states. The masses and widths of the resonances were obtained and the Q2 dependence of the cross-section ratios sigma(rho'->pipi)\sigma(rho) and sigma(rho''->pipi)/sigma(rho) was extracted. The pion form factor obtained in the present analysis is compared to that obtained in e+e- -> pipi.
Olaf Behnke (DESY)