Ratio of the 4He(g, p)3H and 4He(g,n)3He Cross Sections

Abstract

Recent measurements of the 4He(y, p)3H and 4He(y, n)3He cross sections suggest that their ratio in the giant dipole resonance region is approximately I . 6. This is in marked disagreement with detailed model calculations, which have given a ratio close to unity. We here explain why the calculations yielded this result, by using a simple argument based on independent experimental data and some apparently reasonable assumptions. In order to remove the discrepancy with experiment, it appears to be necessary to relax one of these assumptions and to include contributions from states of higher configurations. A satisfactory fit to the cross sections is then possible, but the required isospinmixing matrix element is much larger than that derived from the Coulomb interaction plus a phenomenological charge-symmetry breaking interaction.

Study of the isospin response of theHe4continuum using theHeRaue1, Bland2, Carman3 et al. 1995Phys. Rev. C2110View full textAdd to dashboardCite

“…The Coulomb interaction can account for at most a 10% increase of R~b eyond the simplest expectations based on charge symmetry. Since the lowest lying 1, T=0 state in "He was expected at quite high excitation [13],the CBD value of R can only be accommodated by inclusion of sizable CSB terms in the nucleonnucleon interaction.…”

He4(π,π′p)H3reaction near theMk1, Dehnhard2, Nanda3 et al. 1992Phys. Rev. C

“…. The constant R"measured in this experiment at all angles suggests that the isospin mixing amplitude of Ref [23]. is too large.I I I I I I I I~I~'I I I I~0 I~I 0 I~~I~I 0400 140 MeV B.…”