S. Kameoka

Publications (21)27.28 Total impact

• Article: Erratum: Photoproduction of neutral kaons on a liquid deuterium target in the threshold region [Phys. Rev. C 78, 014001 (2008)]

  K. Tsukada, T. Takahashi, T. Watanabe, Y. Fujii, K. Futatsukawa, O. Hashimoto, K. Hirose, K. Ito, S. Kameoka, H. Kanda, [......], T. Kinoshita, F. Miyahara, T. Nakabayashi, H. Shimizu, T. Tamae, H. Yamazaki, A. Sasaki, O. Konno, P. Bydžovský, M. Sotona
  Physical Review C 02/2011; 83(3):39904. · 3.31 Impact Factor
• Article: The Contribution of the Three-Body Process in the Nonmesonic Weak Decay of the Λ12C Hypernucleus.

  H. Bhang, S. Ajimura, K Aoki, A. Banu, T Fukuda, O Hashimoto, J I Hwang, S. Kameoka, B H Kang, E Kim, [......], Y Sato, M Sekimoto, T Takahashi, H Tamura, K Tanida, A Toyoda, K. Tshoo, K Tsukada, T Watanabe, H. J. Yim
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  ABSTRACT: The serious inconsistency problem between the values of experimental and theoretical Γn /Γp ratio of the nonmesonic weak decay of Λ hypernuclei has been resolved recently. We have shown that the reason behind the problem was the quenching of the nucleon yields which in turn was due to the contribution of the three-body process. We have measured that the branching ratio of the three-body process in nonmesonic weak decay, 0.29±0.13, is so large that the absolute values of Γn and Γp must be determined taking account of the contribution of the 3-body process. In this paper, the recent studies toward the finding of the 3-body process via the exclusive coincidence experiments are presented.
  EPJ Web of Conferences. 01/2010;
• Article: Three-body nonmesonic weak decay of the (Lambda)12C hypernucleus.

  M Kim, S Ajimura, K Aoki, A Banu, H Bhang, T Fukuda, O Hashimoto, J I Hwang, S Kameoka, B H Kang, [......], Y Sato, M Sekimoto, T Takahashi, H Tamura, K Tanida, A Toyoda, K Tshoo, K Tsukada, T Watanabe, H J Yim
  [show abstract] [hide abstract]
  ABSTRACT: We have measured the branching ratio of the three-body process in the nonmesonic weak decay of Lambda12C to be 0.29+/-0.13. This result was obtained by reproducing the nucleon and the nucleon pair yields introducing a measured final state interaction. At the same time, we have determined the absolute decay widths, Gamma(n) and Gamma(p), along with Gamma2N, whose relative ratio has been a long-standing puzzle. Including the three-body process, we have successfully reproduced the nucleon energy distribution, the coincidence two-nucleon angular correlation, and the momentum sum distribution simultaneously.
  Physical Review Letters 10/2009; 103(18):182502. · 7.37 Impact Factor
• Article: Non‐mesonic weak decays of Λ5He and Λ12C hypernuclei using the (π+,K+) reactions

  S. Okada, S. Ajimura, K. Aoki, A. Banu, H. C. Bhang, T. Fukuda, O. Hashimoto, J. I. Hwang, S. Kameoka, B. H. Kang, [......], Y. Sato, M. Sekimoto, S. Shin, T. Takahashi, H. Tamura, K. Tanida, A. Toyoda, K. Tsukada, T. Watanabe, H. J. Yim
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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.
  AIP Conference Proceedings. 04/2008; 1011(1):135-139.
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  Available from: ArXiv

  Article: Photoproduction of neutral kaons on the liquid deuterium target in the threshold region

  K Tsukada, T Takahashi, T Watanabe, Y Fujii, K. Futatsukawa, O Hashimoto, K Hirose, K Ito, S. Kameoka, H Kanda, [......], T Kinoshita, F. Miyahara, T Nakabayashi, H Shimizu, T Tamae, H Yamazaki, A Sasaki, O. Konno, P. Bydzovsky, M. Sotona
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  ABSTRACT: The photoproduction process of neutral kaons on a liquid deuterium target is investigated near the threshold region, Egamma = 0.8-1.1 GeV. K0 events are reconstructed from positive and negative pions, and differential cross sections are derived. Experimental momentum spectra are compared with those calculated in the spectator model using a realistic deuteron wave function. Elementary amplitudes as given by recent isobar models and a simple phenomenological model are used to study the effect of the new data on the angular behavior of the elementary cross section. The data favor a backward-peaked angular distribution of the elementary n(gamma,K0)Lambda process, which provides additional constraints on current models of kaon photoproduction. The present study demonstrates that the n(gamma,K0)Lambda reaction can provide key information on the mechanism of the photoproduction of strangeness.
  12/2007;
• Source

  Available from: Shinji Okada

  Article: Decay asymmetry in non-mesonic weak decay of light Λ -hypernuclei

  T. Maruta, S. Ajimura, K. Aoki, A. Banu, H. Bhang, T. Fukuda, O. Hashimoto, I. Hwang, S. Kameoka, B. H. Kang, [......], H. Park, P. K. Saha, Y. Sato, M. Sekimoto, T. Takahashi, H. Tamura, K. Tanida, A. Toyoda, K. Tsukada, T. Watanabe
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  ABSTRACT: The proton decay asymmetry, αNM p , of the polarized Λ -hypernuclei, 5 ΛHe , 12 ΛC and 11 ΛB , has been investigated to understand the reaction mechanism of the non-mesonic weak-decay process. These Λ -hypernuclei were produced in the highest statistics ever via the (π+, K +) reaction at 1.05GeV/c by using the SKS spectrometer at KEK 12GeV PS. The results show that the αNM p are very small for these s -shell and p -shell hypernuclei.
  European Physical Journal A 08/2007; 33(3):255-258. · 2.19 Impact Factor
• Article: The quenching of nucleon yields in the nonmesonic weak decay of Λ -hypernuclei and the three-body weak decay process

  H. Bhang, S. Ajimura, K. Aoki, A. Banu, T. Fukuda, O. Hashimoto, J. I. Hwang, S. Kameoka, B. H. Kang, E. H. Kim, [......], Y. Sato, M. Sekimoto, S. Shin, T. Takahashi, H. Tamura, K. Tanida, A. Toyota, K. Tsukada, T. Watanabe, H. J. Yim
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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. · 2.19 Impact Factor
• Article: Coincidence Exclusive Measurement of the Nonmesonic Weak Decay of {sub {lambda}}{sup 12}C

  M. J. Kim, S. Ajimura, K. Aoki, A. Banu, H. Bhang, T. Fukuda, O. Hashimoto, J. I. Hwang, S. Kameoka, B. H. Kang, E. H. Kim, J. H. Kim, T. Maruta, Y. Miura, Y. Miyake, T. Nagae, M. Nakamura, S. N. Nakamura, H. Noumi, S. Okada
  [show abstract] [hide abstract]
  ABSTRACT: We have measured the angular correlation of the pair nucleons np and nn emitted from the nonmesonic weak decay (NMWD) of {sub {lambda}}{sup 12}C produced via the ({pi}+,K+) reaction in coincidence measurement. The {lambda}p {yields} np and {lambda}n {yields} 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 {gamma}n/{gamma}p of the partial decay widths {gamma}n({lambda}n {yields} nn) and {gamma}p({lambda}p {yields} np) of {sub {lambda}}{sup 12}C was extracted to be 0.51 {+-} 0.13(stat){+-}0.04(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 {gamma}n/{gamma}p ratio of {sub {lambda}}{sup 12}C (p-shell) is close to that of {sub {lambda}}{sup 5}He (s-shell). The results are consistent with those of recent theoretical calculations.
  AIP Conference Proceedings 07/2006; 842(1).
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  Available from: Shinji Okada

  Article: Exclusive measurement of the nonmesonic weak decay of the lambda(5)He hypernucleus.

  B H Kang, H Bhang, E H Kim, J H Kim, M J Kim, H J Yim, S Ajimura, Y Miyake, K Aoki, T Nagae, [......], T Takahashi, H Tamura, K Tsukada, T Watanabe, J I Hwang, T Maruta, M Nakamura, S Okada, H Park, K Tanida
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  ABSTRACT: We performed a coincidence measurement of two nucleons emitted from the nonmesonic weak decay of lambda(5)He formed via the 6Li(pi+, K+) reaction. The energies of the 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 weak reactions of lambda p --> np and lambda n --> nn, respectively. The ratio of the nucleon pair numbers was N(nn)/N(np) = 0.45 +/- 0.11(stat) +/- 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 and/or direct-quark exchange picture.
  Physical Review Letters 02/2006; 96(6):062301. · 7.37 Impact Factor
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  Available from: Shinji Okada

  Article: Coincidence Measurement of the Nonmesonic Weak Decay of ^{12}_{Lambda}C

  M J Kim, S. Ajimura, K Aoki, A. Banu, H. Bhang, T Fukuda, O Hashimoto, J I Hwang, S. Kameoka, B H Kang, [......], Y Sato, M Sekimoto, S Shin, T Takahashi, H Tamura, K Tanida, A Toyoda, K Tsukada, T Watanabe, H. J. Yim
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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 ^{12}_{Lambda}C produced via the (pi^+,K^+) reaction in coincidence measurement. The Lambda p -> np and Lambda n -> 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 N_{nn} and N_{np}, the ratio Gamma_n/Gamma_p of the partial decay widths Gamma_n(Lambda n -> nn) and Gamma_p(Lambda p -> np) of ^{12}_{Lambda}C 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 Gamma_n/Gamma_p ratio of ^{12}_{Lambda}C (p-shell) is close to that of ^5_{Lambda}He (s-shell). The results are consistent with those of recent theoretical calculations. Comment: 13 pages, 4figures, 1 table,re-submitted to Physics Letters B
  01/2006;
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  Available from: Shinji Okada

  Article: Exclusive proton asymmetry measurement in non-mesonic weak decay of polarized 5_Lambda_He

  T. Maruta, S. Ajimura, K Aoki, A. Banu, H. Bhang, T Fukuda, O Hashimoto, J I Hwang, S. Kameoka, B H Kang, [......], P. K. Saha, Y Sato, M Sekimoto, T Takahashi, H Tamura, K Tanida, A Toyoda, K Tsukada, T Watanabe, H. J. Yim
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  ABSTRACT: The asymmetry parameter alpha_p^NM for a proton exclusively emitted in the Lambda p -> np process was, for the first time, measured in the non-mesonic weak decay of a polarized 5_La,bda_He hypernucleus by selecting the proton-neutron pairs emitted in the back-to-back kinematics. The highly polarized 5_Lambda_He was abundantly produced with the (pi+,K+) reaction at 1.05GeV/c in the scattering angular range of +-15$ degrees. The obtained value alpha_p^NM=0.31+-0.22, as well as that for inclusive protons, alpha_p^NM=0.11+-0.08+-0.04, largely contradicts recent theoretical values of around -0.6, although these calculations well reproduce the branching ratios of non-mesonic weak decay.
  10/2005;
• Source

  Available from: Shinji Okada

  Article: Nucleon-nucleon coincidence measurement in the non-mesonic weak decay of 5_Lambda-He and 12_Lambda-C hypernuclei

  S Okada, S. Ajimura, K Aoki, A. Banu, H. C. Bhang, T Fukuda, O Hashimoto, J I Hwang, S. Kameoka, B H Kang, [......], P. K. Saha, Y Sato, M Sekimoto, T Takahashi, H Tamura, K Tanida, A Toyoda, K Tsukada, T Watanabe, H. J. Yim
  [show abstract] [hide abstract]
  ABSTRACT: We have measured both yields of neutron-proton and neutron-neutron pairs emitted from the non-mesonic weak decay process of 5_Lambda-He and 12_Lambda-C hypernuclei produced via the (pi^+,K^+) reaction for the first time. We observed clean back-to-back correlation of the np- and nn-pairs in the coincidence spectra for both hypernuclei. The ratio of those back-to-back pair yields, Nnn / Nnp, must be close to the ratio of neutron- and proton-induced decay widths of the decay, Gn(Lambda n -> nn)/Gp(Lambda p -> np). The obtained ratios for each hypernuclei support recent calculations based on short-range interactions. Comment: 4 pages, 1 figure, International Nuclear Physics Conference (INPC 2004), Goteborg, Sweden, June 27 - July 2, 2004, to appear in Nuclear Physics A
  11/2004;
• Article: Neutron and proton energy spectra from the non-mesonic weak decays of HeΛ5 and CΛ12

  S. Okada, S. Ajimura, K. Aoki, A. Banu, H. C. Bhang, T. Fukuda, O. Hashimoto, J. I. Hwang, S. Kameoka, B. H. Kang, [......], P. K. Saha, Y. Sato, M. Sekimoto, T. Takahashi, H. Tamura, K. Tanida, A. Toyoda, K. Tsukada, T. Watanabe, H. J. Yim
  [show abstract] [hide abstract]
  ABSTRACT: We have simultaneously measured the energy spectra of neutrons and protons emitted in the non-mesonic weak decays of HeΛ5 and CΛ12 hypernuclei produced via the (π+,K+) reaction with much higher statistics than those of previous experiments. The neutron-to-proton yield ratios for both hypernuclei at a high energy threshold (60 MeV) were approximately equal to two, which suggests that the ratio of the neutron- and proton-induced decay channels, Γn(Λn→nn)/Γp(Λp→np), is about 0.5. In the neutron energy spectra, we found that the yield of the low-energy component is unexpectedly large, even for HeΛ5.
  Physics Letters B 08/2004; 597:249-256. · 3.95 Impact Factor
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  Available from: Shinji Okada

  Article: Neutron and proton energy spectra from the non-mesonic weak decays of 5_Lambda-He and 12_Lambda-C

  S Okada, S Ajimura, K Aoki, A Banu, H C Bhang, T Fukuda, O Hashimoto, J I Hwang, S Kameoka, B H Kang, [......], P K Saha, Y Sato, M Sekimoto, T Takahashi, H Tamura, K Tanida, A Toyoda, K Tsukada, T Watanabe, H J Yim
  [show abstract] [hide abstract]
  ABSTRACT: We have simultaneously measured the energy spectra of neutrons and protons emitted in the non-mesonic weak decays of 5 Λ He and 12 Λ C hypernuclei produced via the (π + ,K +) reaction with much higher statistics over those of previous experi-ments. The neutron-to-proton yield ratios for both hypernuclei at a high energy threshold (60 MeV) were approximately equal to two, which suggests that the ratio of the neutron-and proton-induced decay channels, Γ n (Λn → nn)/Γ p (Λp → np), is about 0.5. In the neutron energy spectra, we found that the yield of the low-energy component is unexpectedly large, even for 5 Λ He.
  07/2004;
• Article: A Recent Experiment with Hyperball

  Y. Miura, S. Ajimura, Y. Fujii, T. Fukuda, O. Hashimoto, H. Hotchi, K. Imai, W. Imoto, Y. Kakiguchi, S. Kameoka, [......], P. K. Saha, T. Saitoh, Y. Sato, M. Sekimoto, T. Takahashi, H. Tamura, K. Tanida, A. Toyoda, M. Ukai, H. Yamauchi
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  ABSTRACT: Using a germanium detector array, Hyperball, we have measured γ rays from several Λ hypernuclei. In the previous experiments, spin-dependence of Λ N effective interaction was investigated. In the latest experiment, we have studied 11Λ B in which six γ transitions have been observed. The result of this experiment suggests that the level structure is quite different from a theoretical prediction based on the Λ N spin-dependent effective interaction parameters determined in the previous experiments.
  Acta Physica Polonica Series B 02/2004; 35:1019. · 0.90 Impact Factor
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  Available from: Shinji Okada

  Article: Measurement of the $\pi^-$ decay width of $^5_\Lambda$He

  S. Kameoka, S. Ajimura, K Aoki, A. Banu, H. C. Bhang, T Fukuda, O Hashimoto, J I Hwang, B H Kang, E H Kim, [......], P. K. Saha, Y Sato, M Sekimoto, T Takahashi, H Tamura, K Tanida, A Toyoda, K Tsukada, T Watanabe, H. J. Yim
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  ABSTRACT: We have precisely measured $\Lambda \to p\pi^-$ decay width of \5LHe and demonstrated significantly larger $\alpha$ -$\Lambda$ overlap than expected from the central repulsion $\alpha$-$\Lambda$ potential, which is derived from YNG \Lambda$-nucleon interaction. Comment: 4 pages, 3 figures
  02/2004;
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  Available from: Shinji Okada

  Article: pi^0 decay branching ratios of 5_Lambda-He and 12_Lambda-C hypernuclei

  S Okada, S. Ajimura, K Aoki, A. Banu, H. C. Bhang, T Fukuda, O Hashimoto, J I Hwang, S. Kameoka, B H Kang, [......], P. K. Saha, Y Sato, M Sekimoto, T Takahashi, H Tamura, K Tanida, A Toyoda, K Tsukada, T Watanabe, H. J. Yim
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  ABSTRACT: We precisely measured pi^0 branching ratios of 5_Lambda-He and 12_Lambda-C hypernuclei produced via (pi^+,k^+) reaction. Using these pi^0 branching ratios with the pi^- branching ratios and the lifetimes, we obtained the pi^0 decay widths and the non-mesonic weak decay widths at high statistics with the accuracy of ~5 % (stat) for both hypernuclei. Comment: 4pages, 4figures, International Conference on Hypernuclear and Strange Particle Physics (HYP2003)
  02/2004;
• Article: Study of double pion photoproduction on the deuteron

  K. Hirose, M. Ejima, T. Fujibayashi, Y. Fujii, K. Futatsukawa, O. Hashimoto, T. Ishikawa, S. Kameoka, H. Kanda, F. Kato, [......], T. Terasawa, H. Tsubota, K. Tsukada, D. Uchida, M. Ukai, M. Wakamatsu, T. Watanabe, H. Yamauchi, H. Yamazaki, K. Yawata
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  ABSTRACT: The π+π− photoproductions on the proton and deuteron have been studied in a photon energy range of 0.8–1.1 GeV at the Laboratory of Nuclear Science, Tohoku University. Charged pions and protons were detected using Neutral Kaon Spectrometer. We obtained the cross sections for the p(γ,pπ+π−) and d(γ,pπ+π−)n. The quasi-free process with a neutron spectator was extracted by the neutron momentum cut of pn>0.3 GeV/c. The cross section for the Δ++Δ− production was deduced in the non-quasi-free process of the γd→pnπ+π−. It was 13.4±0.4 μb at Eγ=0.82 GeV.
  Physics Letters B.
• Article: The Contribution of the Three-Body Process in the Nonmesonic Weak Decay of the

  H. Bhang, S. Ajimura, K Aoki, A. Banu, T Fukuda, O Hashimoto, J I Hwang, S. Kameoka, B H Kang, E Kim, [......], Y Sato, M Sekimoto, T Takahashi, H Tamura, K Tanida, A Toyoda, K. Tshoo, K Tsukada, T Watanabe, H. J. Yim
  http://dx.doi.org/10.1051/epjconf/20100305013.
• Article: Coincidence measurement of the nonmesonic weak decay of 12ΛC

  M.J. Kim, S. Ajimura, K. Aoki, A. Banu, H. Bhang, T. Fukuda, O. Hashimoto, J.I. Hwang, S. Kameoka, B.H. Kang, [......], Y. Sato, M. Sekimoto, S. Shin, T. Takahashi, H. Tamura, K. Tanida, A. Toyoda, K. Tsukada, T. Watanabe, H.J. Yim
  [show abstract] [hide abstract]
  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.
  Physics Letters B.