Hard bremsstrahlung in the pp→ppγ reaction

The pp→ppγ reaction has been measured at a beam energy of 310 MeV by detecting both final protons in the PROMICE-WASA facility and identifying a missing-mass peak. For those events where the pp excitation is less than 3 MeV, the final diproton is almost purely in the S01 state and, under these conditions, there is complete coverage in the photon c.m. angle θγ. The linear behaviour observed in cos2θγ shows that there is almost no influence of an E2 multipole at this energy, though the E1 and M2 must be rather similar in size.