225 research outputs found

    On the role of ground state correlations in hypernuclear non-mesonic weak decay

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    The contribution of ground state correlations (GSC) to the non--mesonic weak decay of Λ12^{12}_\LambdaC and other medium to heavy hypernuclei is studied within a nuclear matter formalism implemented in a local density approximation. We adopt a weak transition potential including the exchange of the complete octets of pseudoscalar and vector mesons as well as a residual strong interaction modeled on the Bonn potential. Leading GSC contributions, at first order in the residual strong interaction, are introduced on the same footing for all isospin channels of one-- and two--nucleon induced decays. Together with fermion antisymmetrization, GSC turn out to be important for an accurate determination of the decay widths. Besides opening the two--nucleon stimulated decay channels, for Λ12^{12}_\LambdaC GSC are responsible for 14% of the rate Γ1\Gamma_1 while increasing the Γn/Γp\Gamma_{n}/\Gamma_{p} ratio by 4%. Our final results for Λ12^{12}_\LambdaC are: ΓNM=0.98\Gamma_{\rm NM}=0.98, Γn/Γp=0.34\Gamma_{n}/\Gamma_{p}=0.34 and Γ2/ΓNM=0.26\Gamma_2/\Gamma_{\rm NM}=0.26. The saturation property of ΓNM\Gamma_{\rm NM} with increasing hypernuclear mass number is clearly observed. The agreement with data of our predictions for ΓNM\Gamma_{\rm NM}, Γn/Γp\Gamma_n/\Gamma_p and Γ2\Gamma_2 is rather good.Comment: 32 pages, 9 figure

    Relationships between nonmesonic-weak-decays in different hypernuclei

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    Using as a tool the s-wave approximation (sWA), this work demonstrates that the nonmesonic weak decay transition rates Γn\Gamma_{n} and Γp\Gamma_{p} can be expressed in all hypernuclei up to Λ29^{29}_\Lambda Si (and very likely in heavier ones too) in the same way as in the s-shell hypernuclei, i.e. as a linear combination of only three elementary transition rates. This finding leads to the analytic prediction that, independently of the transition mechanism, all hypernuclei that are on the stability line (N = Z), i.e. Λ5^5_\Lambda He, Λ7^7_\Lambda Li, Λ9^9_\Lambda Be, Λ11^{11}_\LambdaB, Λ13^{13}_\Lambda C, Λ17^{17}_\Lambda O, Λ29^{29}_\Lambda Si, etc should roughly have the same ratio Γn/Γp\Gamma_{n}/\Gamma_{p}, the magnitude of which rapidly increases when one approaches the neutron drip-line (N >> Z), and opposite happens when one goes toward the proton drip-line (N << Z).Comment: 7 pages, 1 figur

    A systematic study on the binding energy of Λ\Lambda hypernuclei

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    In this paper, we calculated the binding energy per baryon of the Λ\Lambda hypernuclei systemically, using the relativistic mean field theory (RMF) in a statistic frame. Some resemble properties are found among most of the hypernuclei found in experiments. The data show that a Λ\Lambda hypernucleus will be more stable, if it is composed of a Λ\Lambda hyperon adding to a stable normal nuclear core, or a Λ\Lambda hyperon replacing a neutron in a stable normal nuclear core. According to our calculations, existences of some new Λ\Lambda hypernuclei are predicted under the frame of RMF.Comment: 8 pages, 6 figures, 3 table

    Sigma Exchange in the Nonmesonic Decays of Light Hypernuclei and Violation of the Delta I=1/2 Rule

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    Nonmesonic weak decays of s-shell hypernuclei are analyzed in microscopic models for the Lambda N to NN weak interaction. A scalar-isoscalar meson, sigma, is introduced and its importance in accounting the decay rates, n/p ratios and proton asymmetry is demonstrated. Possible violation of the Delta I=1/2 rule in the nonmesonic weak decay of Lambda is discussed in a phenomenological analysis and several useful constraints are presented. The microscopic calculation shows that the current experimental data indicate a large violation of the Delta I=1/2 rule, although no definite conclusion can be derived due to large ambiguity of the decay rate of {^4_Lambda H}.Comment: 13 pages, 5 figure

    Inclusive pion double charge exchange on O-16 above the delta resonance

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    The forward inclusive pion double charge exchange reaction, ^{16}O(pi^-,pi^+)X, at T_0 = 0.50 and 0.75 GeV has been studied in the kinematical region where an additional pion production is forbidden by energy-momentum conservation. The experiment was performed with the SKS spectrometer at KEK PS. The measured ratio of double charge exchange cross-section for these energies dsigma(0.50 GeV)/dOmega / dsigma(0.75 GeV)/dOmega = 1.7 +/- 0.2, disagrees with the value of 7.2 predicted within the conventional sequential single charge exchange mechanism. Possible reasons for the disagreement are discussed in connection with the Glauber inelastic rescatterings.Comment: 4 pages, 5 figure

    ΛN\Lambda N correlations from the stopped KK^- reaction on 4{}^4He

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    We have investigated correlations of coincident ΛN\Lambda N pairs from the stopped KK^- reaction on 4{}^4He, and clearly observed Λp\Lambda p and Λn\Lambda n branches of the two-nucleon absorption process in the ΛN\Lambda N invariant mass spectra. In addition, non-mesonic reaction channels, which indicate possible exotic signals for the formation of strange multibaryon states, have been identified.Comment: 5 pages, 3 figures, submitted to Physical Review Letter

    Exclusive Measurement of the Nonmesonic Weak Decay of ^{5}_{\Lambda}He Hypernucleus

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    We performed a coincidence measurement of two nucleons emitted from the nonmesonic weak decay (NMWD) of ^{5}_{\Lambda}He formed via the ^{6}Li(\pi^+,K^+) reaction. The energies of two nucleons and the pair number distributions in the opening angle between them were measured. In both np and nn pairs, we observed a clean back-to-back correlation coming from the two-body decay of \Lambda p --> n p and \Lambda n --> n n, respectively. The ratio of the nucleon pair numbers was N_{nn}/N_{np}=0.45 \pm 0.11(stat)\pm 0.03(syst) in the kinematic region of cos(theta_{NN}) < -0.8. Since each decay mode was exclusively detected, the measured ratio should be close to the ratio of \Gamma(\Lambda p --> np)/\Gamma(\Lambda n --> nn). The ratio is consistent with recent theoretical calculations based on the heavy meson/direct quark exchange picture.Comment: Submitted to Phys. Rev. lett., 4 pages, 3 figure

    Proton asymmetry in non-mesonic weak decay of light hypernuclei

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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.Comment: 4pages, 4figures, International Conference on Hypernuclear and Strange Particle Physics (HYP2003
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