Charge symmetry breaking in dd→He4π0 with WASA-at-COSY

Abstract Charge symmetry breaking (CSB) observables are a suitable experimental tool to examine effects induced by quark masses on the nuclear level. Previous high precision data from TRIUMF and IUCF are currently used to develop a consistent description of CSB within the framework of chiral perturbation theory. In this work the experimental studies on the reaction dd → He 4 π 0 have been extended towards higher excess energies in order to provide information on the contribution of p -waves in the final state. For this, an exclusive measurement has been carried out at a beam momentum of p d = 1.2 GeV / c using the WASA-at-COSY facility. The total cross section amounts to σ tot = ( 118 ± 18 stat ± 13 sys ± 8 ext ) pb and first data on the differential cross section are consistent with s -wave pion production.