Isospin symmetry breaking and scaling observed in pion production in p+d reactions

Abstract A stack of annular detectors made of high purity germanium was used to measure p+d→ 3 He +π 0 and p+d→ 3 H +π + differential and total cross sections at beam momenta from 900 to 1050 MeV/ c . The total cross sections are consistent with Δ -excitation. The differential data consist of two components. One corresponds to large momentum transfer from the projectile to the pion, the other to small momentum transfer. The former shows an independence of the slope as function of the momentum transfer  t (scaling). The scale parameter is different for π + and π 0 emission which violates isospin symmetry. The second component which is almost isotropic is in agreement with isospin symmetry. It is approximately a quarter of the total yield in the Δ resonance region.