10 research outputs found
Simple analytical expression for vector hypernuclear asymmetry in nonmesonic decay of 5Λ He and 12Λ C
We present general explicit expressions for a shell-model calculation of the vector hypernuclear parameter in nonmesonic weak decay. We use a widely accepted effective coupling Hamiltonian involving the exchange of the complete pseudoscalar and vector meson octets (π, η, K, ρ, ω, K*). In contrast to the approximated formula widely used in the literature, we correctly treat the contribution of transitions originated from single-proton states beyond the s-shell. Exact and simple analytical expressions are obtained for the particular cases of 5ΛHe and 12ΛC, within the one-pion-exchange model. Numerical computations of the asymmetry parameter, aΛ, are presented. Our results show a qualitative agreement with other theoretical estimates but also a contradiction with recent experimental determinations. Our simple analytical formulas provide a guide in searching the origin of such discrepancies, and they will be useful for helping to solve the hypernuclear weak decay puzzle.Facultad de Ciencias Exacta
Simple analytical expression for vector hypernuclear asymmetry in nonmesonic decay of 5Λ He and 12Λ C
We present general explicit expressions for a shell-model calculation of the vector hypernuclear parameter in nonmesonic weak decay. We use a widely accepted effective coupling Hamiltonian involving the exchange of the complete pseudoscalar and vector meson octets (π, η, K, ρ, ω, K*). In contrast to the approximated formula widely used in the literature, we correctly treat the contribution of transitions originated from single-proton states beyond the s-shell. Exact and simple analytical expressions are obtained for the particular cases of 5ΛHe and 12ΛC, within the one-pion-exchange model. Numerical computations of the asymmetry parameter, aΛ, are presented. Our results show a qualitative agreement with other theoretical estimates but also a contradiction with recent experimental determinations. Our simple analytical formulas provide a guide in searching the origin of such discrepancies, and they will be useful for helping to solve the hypernuclear weak decay puzzle.Facultad de Ciencias Exacta
Weak nonmesonic decay spectra of hypernuclei
We compute one- and two-nucleon kinetic-energy spectra and opening-angle
distributions for the nonmesonic weak decay of several hypernuclei, and compare
our results with some recent data. The decaymics is described by transition
potentials of the one-meson-exchange type, and the nuclear structure aspects by
two versions of the independent-particle shell model (IPSM). In version IPSM-a,
the hole states are treated as stationary, while in version IPSM-b the deep
hole states are considered to be quasi-stationary and are described by
Breit-Wigner distributions.Comment: 3 pages 2 figures. To be published in Nucl. Phys. A; Contribution to
the NN2009 International Conference, Beijing, China, August 200
Simple analytical expression for vector hypernuclear asymmetry in nonmesonic decay of 5Λ He and 12Λ C
We present general explicit expressions for a shell-model calculation of the vector hypernuclear parameter in nonmesonic weak decay. We use a widely accepted effective coupling Hamiltonian involving the exchange of the complete pseudoscalar and vector meson octets (π, η, K, ρ, ω, K*). In contrast to the approximated formula widely used in the literature, we correctly treat the contribution of transitions originated from single-proton states beyond the s-shell. Exact and simple analytical expressions are obtained for the particular cases of 5ΛHe and 12ΛC, within the one-pion-exchange model. Numerical computations of the asymmetry parameter, aΛ, are presented. Our results show a qualitative agreement with other theoretical estimates but also a contradiction with recent experimental determinations. Our simple analytical formulas provide a guide in searching the origin of such discrepancies, and they will be useful for helping to solve the hypernuclear weak decay puzzle.Facultad de Ciencias Exacta
Kinetic energy sum spectra in nonmesonic weak decay of hypernuclei
We evaluate the coincidence spectra in the nonmesonic weak decay (NMWD)
\Lambda N\go nN of hypernuclei He, He,
C, O, and Si, as a function of the
sum of kinetic energies for . The strangeness-changing
transition potential is described by the one-meson-exchange model, with
commonly used parameterization. Two versions of the Independent-Particle Shell
Model (IPSM) are employed to account for the nuclear structure of the final
residual nuclei. They are: (a) IPSM-a, where no correlation, except for the
Pauli principle, is taken into account, and (b) IPSM-b, where the highly
excited hole states are considered to be quasi-stationary and are described by
Breit-Wigner distributions, whose widths are estimated from the experimental
data. All and spectra exhibit a series of peaks in the energy
interval 110 MeV MeV, one for each occupied shell-model state.
The IPSM-a could be a pretty fair approximation for the light He
and He hypernuclei. For the remaining, heavier, hypernuclei it is
very important, however, to take into account the spreading in strength of the
deep-hole states, and bring into play the IPSM-b approach. Notwithstanding the
nuclear model that is employed the results depend only very weakly on the
details of the dynamics involved in the decay process proper. We propose that
the IPSM is the appropriate lowest-order approximation for the theoretical
calculations of the of kinetic energy sum spectra in the NMWD. It is in
comparison to this picture that one should appraise the effects of the final
state interactions and of the two-nucleon-induced decay mode.Comment: v1: 20 pages, 3 figures, 1 table, submitted for publication; v2:
minor corrections, improved figures, published versio
Weak nonmesonic decay spectra of hypernuclei
We compute one- and two-nucleon kinetic-energy spectra and opening-angle distributions for the nonmesonic weak decay of several hypernuclei, and compare our results with some recent data. The decay dynamics is described by transition potentials of the one-meson-exchange type, and the nuclear structure aspects by two versions of the independent-particle shell model (IPSM). In version IPSM-a, the hole states are treated as stationary, while in version IPSM-b the deep-hole ones are considered to be quasi-stationary and are described by Breit-Wigner distributions.Facultad de Ciencias ExactasInstituto de Física La Plat
Simple analytical expression for vector hypernuclear asymmetry in nonmesonic decay ofΛ 5He andΛ 12C
We present general explicit expressions for a shell-model calculation of the vector hypernuclear parameter in nonmesonic weak decay. We use a widely accepted effective coupling Hamiltonian involving the exchange of the complete pseudoscalar and vector meson octets (π, η, K, ρ, ω, K*). In contrast to the approximated formula widely used in the literature, we correctly treat the contribution of transitions originated from single-proton states beyond the s-shell. Exact and simple analytical expressions are obtained for the particular cases of Λ 5He and Λ 12C, within the one-pion-exchange model. Numerical computations of the asymmetry parameter, aΛ, are presented. Our results show a qualitative agreement with other theoretical estimates but also a contradiction with recent experimental determinations. Our simple analytical formulas provide a guide in searching the origin of such discrepancies, and they will be useful for helping to solve the hypernuclear weak decay puzzle