Study of the η'π+π– System in a Charge-Exchange Reaction of Pions with Be at Momentum 29 GeV/c

The first observation of the $$\eta {\kern 1pt} '(958){{\pi }^{ + }}{{\pi }^{ - }}$$ system in the charge-exchange reaction of pions at the VES setup of the U-70 accelerator is reported. The preliminary results of the study are presented. The invariant mass spectrum has a wide maximum at about 2.2 GeV. The $$\eta {\kern 1pt} '{{\rho }^{0}}$$ intermediate state dominates. The cross section is measured for the $${{\pi }^{ - }}{\text{Be}} \to A{\kern 1pt} \eta {\kern 1pt} '{{\pi }^{ + }}{{\pi }^{ - }}$$ reaction, where A consists of nine nucleons (three protons and six neutrons) or eight nucleons and $$\Delta (1232)$$ isobar.