Enhancement in axial charge matrix elements from meson exchange currents
199228 pages
Published in:
- Nucl.Phys.A 542 (1992) 631-658,
- Nucl.Phys.A 569 (1994) 834-834 (erratum)
- Published: 1992
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Abstract: (Elsevier)
The enhancement factor ϵ mec = 1 + δ mec , defined as the ratio of the axial-charge matrix element in first-forbidden beta decay to its impulse-approximation value, is calculated in a meson-exchange model for both light and heavy nuclei. Pion-exchange processes are computed from a chiral-symmetric phenomenological lagrangian and compared with results obtained in the soft-pion approximation. Heavy-meson pair graphs are included, with coupling constants determined from the Bonn potential. Non-relativistic reductions are carried out to leading order and to next-to-leading order. The results are sensitive to the choice of the short-range correlation function used in conjunction with harmonic-oscillator wavefunctions. A ratio of transition matrix elements however is less sensitive to this uncertainty. Our main result comparing a heavy-mass transition with a light-mass one is r ≡ δ mec (A = 208; lg 9 2 → 0 h 9 2 ) δ mec (A = 16; 1 s 1 2 → 0 p 1 2 ) = 1.38 . This result is smaller than the value of 1.58 ± 0.09 deduced by Warburton in a fit between shell-model impulse-approximation matrix elements and experiment.- nucleus: semileptonic decay
- semileptonic decay: nucleus
- S-matrix
- charge: axial
- effect: enhancement
- impulse approximation
- meson: exchange
- exchange: meson
- exchange: current
- current: exchange
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