The interaction effect in n-p capture
Dec, 196445 pages
Published in:
- Nucl.Phys. 74 (1965) 508-532,
- Nucl.Phys.A 95 (1967) 705-705 (erratum)
Report number:
- SLAC-PUB-0059
Citations per year
Abstract: (Elsevier)
The non-relativistic prediction of the n-p capture cross section at a neutron laboratory velocity of 2200 m/sec is evaluated as 302.5±4.0 mb assuming that r s np = 2.73±0.03 fm as predicted by charge independence, or 308.5±5.0 mb if r s np = 2.44±0.11 fm. The smaller value for r s np , derived from the two most recent n-p total cross section measurements, raises serious difficulties with the hypothesis of charge independence, which are discussed. The prediction includes corrections for the shape dependence of the triplet effective range, the deuteron D state probability, and the intermediate range behaviour of the wave functions, which contribute half the quoted uncertainty; these corrections are model independent to within that uncertainty if the longest range part of the interaction is due to one-pion exchange. The experimental value of 334.2±0.5 mb obtained by Cox, Wynchank and Collie therefore shows an interaction effect of 9.5±1.2% (or 7.7±1.5%). A recently proposed approximation based on dispersion theory which would, if accepted, explain two-thirds of the effect, is shown to be quantitatively inadequate. Hence covariant calculations which reduce to this approximation must be rejected, except for those parts of the calculation which give meson current corrections. Stranahan predicts a 2.9% correction coming from the π-N 33 resonance, while the calculation of M. H. Skolnick, interpreted as indicated, gives a non-resonant contribution of 2.2%. Even if these effects could be added, a substantial part of the meson current contribution remains unexplained. It is suggested that at least part of this residual effect might be due to the large π-γ-ϱ coupling recently invoked by Adler and Drell to account for the static magnetic moment of the deuteron and the large forward photopion production cross section in the multi-GeV region.References(4)
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