Production of isoscalar pion pairs in the pd→3Heππ reaction near threshold

The production near threshold of isoscalar pion pairs in the pd→3He(ππ)0 reaction is estimated in a two-step model which successfully describes the production of η, ω and η′ mesons. A virtual pion beam, generated through an NN→dπ reaction on one of the nucleons in the deuteron, produces a second pion via a πN→ππN reaction on the other nucleon. Using the same scale factor as for heavy meson production, the model reproduces the total π0π0 production rate determined at an excess energy of 37 MeV. There are some indications in the data for a suppression of events with low ππ masses, as in the π−p→π0π0n reaction, and this is confirmed within the model. The model suggests that a significant fraction of the charged pion production in the pd→3Heπ+π− reaction at Q=70 MeV might be associated with isoscalar pion pairs, though this does not explain the strong dependence observed on the π+π− relative momentum angle.