The role of Delta(1700) excitation and rho production in double pion photoproduction

Abstract

Recent information on invariant mass distributions of the $\gamma p\to {\pi }^{+}{\pi }^{0}n$ reaction, where previous theoretical models had shown deficiencies, have made more evident the need for new mechanisms, so far neglected or inaccurately included. We have updated a previous model to include new necessary mechanisms. We find that the production of the $\rho$ meson, and the $\Delta (1700)$ excitation, through interference with the dominant terms, are important mechanisms that solve the puzzle of the $\gamma p\to {\pi }^{+}{\pi }^{0}n$ reaction without spoiling the early agreement with the $\gamma p\to {\pi }^{+}{\pi }^{-}p$ and $\gamma p\to {\pi }^0{\pi }^{0}p$ reactions.

Comments: 39 pages, 13 figures (ps files). Final version. To be published in Nucl. Phys. A