Nucleon-nucleon coincidence spectra in the nonmesonic weak decay of lambda hypernuclei and the gamma(n)/gamma(p) puzzle.
By combining a one-meson-exchange model for the LambdaN-->nN transition in finite nuclei with an intranuclear cascade code, we have obtained nucleon-nucleon (angular and energy) coincidence distributions from the nonmesonic weak decay of (5)(Lambda)He and (12)(Lambda)C hypernuclei. Although, due to the elimination of interferences, two-nucleon coincidences are expected to give a cleaner extraction (with respect to single nucleon observables) of the ratio Gamma(n)/Gamma(p) identical with Gamma(Lambdan-->nn)/Gamma(Lambdap-->np), we show that the effect of the final state interactions is still important even when applying favorable energy and angular cuts. The agreement of our results for the ratio N(nn)/N(np) between the number of nn and np emitted pairs with preliminary KEK coincidence data allows us to conclude that Gamma(n)/Gamma(p) for (5)(Lambda)He should be small and close to the value of 0.46 predicted by our meson-exchange model.
Garbarino
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Departament d'Estructura i Constituents de la Matèria, Universitat de Barcelona, E-08028 Barcelona, Spain.
Parreño
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Ramos
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