Two-Body Effective-Mass Spectra in the Products of the Reactionγ+p→p+π++π−and theσResonance

Abstract

By means of spark chambers and counters we measured the (${\pi }^{+}, {\pi }^{-}$) and (${\pi }^{\pm }$, $p$) invariant-mass spectra obtained from the products of the reaction $\gamma +p\to p+{\pi }^{+}+{\pi }^{-}$. They are in disagreement with the Cutkosky-Zachariasen model which takes into account the effect of the $\frac{3}{2}$, $\frac{3}{2}$ nucleon isobar. To fit our data we introduce a $\pi -\pi$ final-state enhancement factor with resonant behavior. The resonance energy is around 380 MeV.