Reaction pp rightarrow pp pi pi pi as a background for hadronic decays of the eta^{{prime}}_{} meson

Isospin violating hadronic decays of the $ eta$ and $ eta{^prime}$ mesons into 3 $ pi$ mesons are driven by a term in the QCD Lagrangian proportional to the mass difference of the d and u quarks. The source giving large yield of the mesons for such decay studies are pp interactions close to the respective kinematical thresholds. The most important physics background for $ eta$ , $ eta{^prime}$ $ rightarrow$ $ pi$ $ pi$ $ pi$ is coming from direct three-pion production reactions. In case of the $ eta$ meson the background for the decays is relatively low ( $ approx$ 10% . The purpose of this article is to provide an estimate of the direct pion production background for the $ eta{^prime}$ $ rightarrow$ 3 $ pi$ decays. Using the inclusive data from the COSY-11 experiment we have extracted the differential cross-section for the pp $ rightarrow$ pp -multipion production reactions with the invariant mass of the pions equal to the $ eta{^prime}$ meson mass and estimated an upper limit for the signal to background ratio for studies of the $ eta{^prime}$ $ rightarrow$ $ pi^{+}_{}$ $ pi^{-}_{}$ $ pi^{0}_{}$ decay.