Observation of inverse diproton photodisintegration at intermediate energies

TL;DR

This study observes inverse diproton photodisintegration at intermediate energies, measuring cross sections that suggest multipole contributions and potential Delta(1232) resonance effects, providing new insights into proton pair interactions.

Contribution

First experimental measurement of pp->{pp}_sγ reaction at intermediate energies, revealing angular dependence and possible resonance influence, advancing understanding of diproton photodisintegration.

Findings

Cross sections increase steeply with angle, indicating E1 and E2 multipole contributions.

Measured cross sections are 10^{-3} to 10^{-2} times those of np->dγ.

Cross section growth with energy suggests Delta(1232) resonance influence.

Abstract

The reaction pp->{pp}_s\gamma, where {pp}_s is a proton pair with an excitation energy E_{pp}<3 MeV, has been observed with the ANKE spectrometer at COSY-Juelich for proton beam energies of T_p=0.353, 0.500, and 0.550 GeV. This is equivalent to photodisintegration of a free 1S_0 diproton for photon energies E\gamma ~ T_p/2. The differential cross sections measured for c.m. angles 0 deg.<\theta_{pp}<20 deg. 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->d\gamma 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.