Observation of Inverse Diproton Photodisintegration at Intermediate Energies

Abstract

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-Jülich for proton beam energies of T_{p}=0.353, 0.500, and 0.550 GeV. This is equivalent to photodisintegration of a free 1S0 diproton for photon energies E_{gamma} approximately T_{p}/2. The differential cross sections measured for c.m. angles 0 degrees <theta_{pp}<20 degrees exhibit a steep increase with angle that is compatible with E1 and E2 multipole contributions. The ratio of the measured cross sections to those of np-->gammad 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.

The legacy of the experimental hadron physics programme at COSY

“…Missing-mass distributions from the ANKE experiment are shown for two beam energies in Fig. 34 [111,112]. Although there is no real difficulty in identifying the γ peak at 353 MeV, the same is not true at 625 MeV where, for kinematic reasons, the π 0 peak is considerably wider.…”

“…This means that the acceptance for two protons from a pp → ppX reaction is maximal when these have similar momentum vectors, i.e., the excitation energy E pp in the final pp rest frame is small. In such cases the Pauli principle requires the diproton to be in the 1 111,112]. The expected π 0 position is indicated by the arrow.…”

“…at six energies between 353 MeV and 800 MeV [111,112]. Such small angle studies were possible at ANKE because of the absence of a beam-pipe hole.…”

“…Angular dependence of the differential cross section for the pp → {pp}sγ reaction at four beam energies measured at ANKE[111,112]. Experimental results are shown at 353 MeV by (black) circles, at 500 MeV by (red) squares, at 550 MeV by (blue) triangles, and at 700 MeV by (magenta) stars.…”

Measurement and analysis of thepp→ppγreaction at 310 MeV

“…Data on the hardest part of the pp bremsstrahlung spectrum were also obtained at the COSY-ANKE magnetic spectrometer by selecting the two final protons with E pp < 3 MeV [12,13]. A proton beam energy range from 353 to 800 MeV was investigated but only for CM photon angles θ γ , where cos θ γ > 0.95.…”