Simple analytical expression for vector hypernuclear asymmetry in nonmesonic decay of $^5_Lambda$He and $^{12}_\Lambda$C

• Autor(a) principal: Barbero,César
• Data de Publicação: 2006
• Outros Autores: Krmpotic,Francisco, Galeão,Alfredo P.
• Tipo de documento: Artigo
• Idioma: eng
• Título da fonte: Brazilian Journal of Physics
• Texto Completo: http://old.scielo.br/scielo.php?script=sci_arttext&pid=S0103-97332006000800005
• topic: Hypernuclear decay; Asymmetry parameter; One-meson-exchange model

We present general explicit expressions for a shell-model calculationof the vector hypernuclear parameter in nonmesonic weak decay. We use a widely accepted effective coupling Hamiltonian involving theexchange of the complete pseudoscalar and vector meson octets(<FONT FACE=Symbol>p, h</FONT>, K, <FONT FACE=Symbol>r, w</FONT>, K*). In contrast to the approximated formula widely used in the literature,we correctly treat the contribution of transitions originated fromsingle-proton states beyond the s-shell. Exact and simple analytical expressions are obtained for the particularcases of $^5_Lambda$He and $^{12}_\Lambda$C, within theone-pion-exchange model. Numerical computations of the asymmetry parameter, $a_\Lambda$, are presented. Our results show a qualitative agreementwith other theoretical estimates but also acontradiction with recent experimental determinations. Our simple analytical formulas provide a guide in searchingthe origin of such discrepancies, andthey will be useful for helping to solve the hypernuclearweak decay puzzle.