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تسجيل مستخدم جديدTwo-pion-exchange in the non-mesonic weak decay of $Lambda$-hypernuclei
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The non-mesonic weak decay of $Lambda$--hypernuclei is studied within a one-meson-exchange potential supplemented by a chirally motivated two-pion-exchange mechanism. The effects of final state interactions on the outgoing nucleons are also taken into account. In view of the severe discrepancies between theoretical expectations and experimental data, particular attention is payed to the asymmetry of the protons emitted by polarized hypernuclei. The one-meson-exchange model describes the non-mesonic rates and the neutron-to-proton ratio satisfactorily but predicts a too large and negative asymmetry parameter. The uncorrelated and correlated two-pion mechanisms change the rates moderately, thus maintaining the agreement with experiment. The modification in the strength and sign of some decay amplitudes becomes crucial and produces asymmetry parameters which lie well within the experimental observations.
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The non-mesonic weak decay of polarized Lambda-hypernuclei is studied for the first time by taking into account, with a Monte Carlo intranuclear cascade code, the nucleon final state interactions. A one-meson-exchange model is employed to describe th
e Lambda N-> n N processes in a finite nucleus framework. The relationship between the intrinsic Lambda asymmetry parameter a_Lambda and the asymmetry a^M_Lambda accessible in experiments is discussed. A strong dependence of a^M_Lambda on nucleon final state interactions and detection threshold is obtained. Our results for a^M_Lambda are consistent with ^{11}_Lambda B and ^{12}_Lambda C data but disagree with observations in ^5_Lambda He.
The non--mesonic weak decay of double--$Lambda$ hypernuclei is studied within a microscopic diagrammatic approach. Besides the nucleon--induced mechanism, $Lambda Nto nN$, widely studied in single--$Lambda$ hypernuclei, additional hyperon--induced me
chanisms, $Lambda Lambdato Lambda n$, $Lambda Lambdato Sigma^0 n$ and $Lambda Lambdato Sigma^-p$, are accessible in double--$Lambda$ hypernuclei and are investigated here. As in previous works on single--$Lambda$ hypernuclei, we adopt a nuclear matter formalism extended to finite nuclei via the local density approximation and a one--meson exchange weak transition potential (including the ground state pseudoscalar and vector octets mesons) supplemented by correlated and uncorrelated two--pion--exchange contributions. The weak decay rates are evaluated for hypernuclei in the region of the experimentally accessible light hypernuclei $^{10}_{LambdaLambda}$Be and $^{13}_{LambdaLambda}$B. Our predictions are compared with a few previous evaluations. The rate for the $Lambda Lambdato Lambda n$ decay is dominated by $K$--, $K^*$-- and $eta$--exchange and turns out to be about 2.5% of the free $Lambda$ decay rate, $Gamma_{Lambda}^{rm free}$, while the total rate for the $Lambda Lambdato Sigma^0 n$ and $Lambda Lambdato Sigma^- p$ decays, dominated by $pi$--exchange, amounts to about 0.25% of $Gamma_{Lambda}^{rm free}$. The experimental measurement of these decays would be essential for the beginning of a systematic study of the non--mesonic decay of strangeness $-2$ hypernuclei. This field of research could also shed light on the possible existence and nature of the $H$--dibaryon.
The decay of $Lambda$-hypernuclei without pion emission, known as Non Mesonic Weak Decay (NMWD), gives an effective tool to investigate $Delta$S=1 four-baryon interactions. It was theoretically suggested that the two-nucleon induced mechanism could p
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We have obtained the decay asymmetry parameters in non-mesonic weak decay of polarized Lambda-hypernuclei by measuring the proton asymmetry. The polarized Lambda-hypernuclei, 5_Lambda-He, 12_Lambda-C, and 11_Lambda-B, were produced in high statistics
via the (pi^+,k^+) reaction at 1.05 GeV/c in the forward angles. Preliminary analysis shows that the decay asymmetry parameters are very small for these s-shell and p-shell hypernuclei.
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