S. Shin

Ewha Womans University, Sŏul, Seoul, South Korea

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Publications (4)3.26 Total impact

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    ABSTRACT: Fundamental interest on Non Mesonic Weak Decay (NMWD) is that it provides practically the only means to study the elementary ΔS = 1 baryon-baryon weak interaction process, ΛN→NN (Λp → np and Λn → nn), since it is difficult to be realized in the free space. Thanks to the recent developments in experimental and theoretical studies, the relative strength of two channels, the Γn/Γp ratios whose experimental and theoretical values have showed a long standing discrepancy have been converged to ~ 0.5 and the discrepancy problem finally has been solved.1–3 However, despite the progresses, the decay interaction of NMWD is not yet well established and there remain the important issues such as the discrepancy of asymmetry parameter between experimental and theoretical values, confirmation of 3-body NMWD process, and whether the I = 1/2 rule for ΔS = 1 decay would hold or not in NMWD. Especially the recent experimental indication of the 3-body decay process ΛNN→NNN whose contribution was predicted to be significant in the theoretical calculations seems to be strong and showed a surprisingly large contribution in the quenching of singles and coincidence nucleon yields in NMWD. Recent results of the asymmetry parameter αnm of NMWD showed small values for both s-shell and p-shell and consistent with each other. However, the discrepancy of the theoretical values from those of experimental ones remains to be understood. It now becomes one of the urgent issues in NMWD study to determine the contribution of the 3-body NMWD channel experimentally, in order to understand the discrepancy of the asymmetry papameter, and to test the ΔI = 1/2 rule for NMWD which are the main purposes of J-PARC 50 GeV PS experiment, E18 and E22.
    International Journal of Modern Physics E 12/2010; 19(12):2558-2565. DOI:10.1142/S0218301310017083 · 0.84 Impact Factor
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    ABSTRACT: We have measured for the first time yields of both neutron‐proton and neutron‐neutron pairs emitted from the non‐mesonic weak decay of the Λ5He and Λ12C hypernuclei, produced via the (π+,K+) reaction. From the yields of both the back‐to‐back np‐pair events and nn‐pair events, we have directly determined the ratio of the neutron‐ and proton‐induced decay widths, Γn(Λn→nn)/Γp(Λp→np). Meanwhile, we have also determined the quenching of the observed numbers of single nucleons and coincident nucleon pairs compared with theoretical calculations. Our results suggest that contributions from the two‐nucleon‐induced three‐body process ΛNN→NNN are significant.
    04/2008; 1011(1):135-139. DOI:10.1063/1.2932278
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    ABSTRACT: Recent exclusive coincidence measurements of non-mesonic weak decays (NMWD) reported for the ratio of the partial decay width of neutron-induced-to-proton-induced NMWD, Γn/Γp , values of 0.45±0.11±0.03 and 0.51±0.13±0.04 for 5lam and 12 Λ C , respectively. These observations agree well with the improved theoretical Γn/Γp ratios which are in the range of 0.3-0.7. It appears that the long-standing discrepancy between the experimental and theoretical values of Γn/Γp has finally been solved. However, when compared to the results of intra-nuclear cascade (INC) calculations, the observed numbers of both single nucleons and coincident nucleon pairs are strongly quenched. The quenching of the proton yield observed previously has been interpreted as an increase of the Γn/Γp ratio. On the other hand, significant contributions from the two-nucleon-induced three-body process ΛNN → nNN are predicted. Indeed, the angular correlation of the emitted nucleon pairs in the NMWD of 12 Λ C showed not only decay events in back-to-back kinematics, but also events with non-back-to-back kinematics. In this paper we show that the difficulties to extract the correct Γn/Γp ratio from the proton spectra is related to the three-body weak-interaction process which strongly quenches the nucleon yields.
    European Physical Journal A 01/2007; 33(3):259-263. DOI:10.1140/epja/i2007-10470-x · 2.42 Impact Factor
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    ABSTRACT: We have measured the angular correlation of the pair nucleons np and nn emitted from the nonmesonic weak decay (NMWD) of 12ΛC produced via the (π+,K+) reaction in coincidence measurement. The Λp→np and Λn→nn modes were clearly identified by measuring the back-to-back correlation of the emitted nucleon pairs which is the characteristic of two-body kinematics. From the measured nucleon pair numbers Nnn and Nnp, the ratio Γn/Γp of the partial decay widths Γn(Λn→nn) and Γp(Λp→np) of 12ΛC was extracted to be 0.51±0.13(stat)±0.05(syst); this result is almost free from the ambiguity due to the nuclear final state interaction and 3-body decay process, which were inherent in the previous results. The obtained Γn/Γp ratio of 12ΛC (p-shell) is close to that of 5ΛHe (s-shell). The results are consistent with those of recent theoretical calculations.