Exclusive measurements of pd→He3ππ: The ABC effect revisited

Exclusive measurements of the reactions pd→He3π+π− and pd→He3π0π0 have been carried out at Tp=0.893GeV at the CELSIUS storage ring using the WASA detector. The π+π− channel evidences a pronounced enhancement at low invariant ππ masses-as anticipated from previous inclusive measurements of the ABC effect. This enhancement is seen to be even much larger in the isoscalar π0π0 channel. The differential distributions prove this enhancement to be of scalar-isoscalar nature. ΔΔ calculations give a good description of the data, if a boundstate condition is imposed for the intermediate ΔΔ system.