P+D radiative capture and mesonic effects

We have measured precise data for the vector- and tensor-analyzing powers of the radiative capture reaction p+d→3He+γ at deuteron energies of 29 MeV and 45 MeV. These data are compared to modern three-body calculations that treat both the bound and the continuum state exactly. We show that the analyzing powers exhibit very large effects of meson exchange currents, despite the fact that the momentum transfers involved are very small. The MEC are well described by theory. We also find that, at extreme angles, relativistic effects are important.