Observation of inverse diproton photodisintegration at intermediate energies

The fundamental reaction pp ->{pp}(s)gamma, where {pp}(s) is a proton pair with low excitation energy, has been observed with the ANKE spectrometer at COSY-Julich for proton beam energies of T-p=0.353, 0.500, and 0.550 GeV. This is equivalent to photodisintegration of a free S-1(0) diproton for photon energies E-gamma approximate to T-p/2. The differential cross sections measured for c.m. angles 0 degrees gamma d is on the 10(-3)-10(-2) level. The increase of the pp ->{pp}(s)gamma cross section with T-p might reflect the influence of the Delta(1232) excitation