The reaction NN → dπ studied by target rescattering at CLAS

Using rescattering in exclusive meson photoproduction (γp → Nπ), the reaction cross sections for np → d π⁰ and pp → d π⁺ have been measured using the CLAS detector.  The total cross sections, as a function of the center-of-mass energy, W, show a peak in the invariant mass of the deuteron-pion system at about 2145 MeV, which corresponds to the known resonance from the attractive N△ channel with isospin I=1.  Results for the pp → d π⁺ reaction agree well with previous measurements, whereas the np → d π⁰ cross sections have not been previously determined.  The ratio between these two total cross sections at the resonance peak is expected to follow predictions from isospin symmetry. Because both reactions are measured simultaneously, some systematic uncertainties cancel.  Our preliminary results on these ratios indicate a deviation from predictions, which suggests that the reaction mechanism might be more complicated.