The Contribution of the Three-Body Process in the Nonmesonic Weak Decay of Λ Hypernuclei

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The Contribution of the Three-Body Process in the Nonmesonic Weak Decay of Λ Hypernuclei. H. Bhang (Seoul National University) For KEK-PS E508 Collaboration FB09 Bonn, Germany Aug. 31-Sep. 05, 2009. I. The Weak Decay Modes of Λ Hypernuclei . - PowerPoint PPT Presentation

Text of The Contribution of the Three-Body Process in the Nonmesonic Weak Decay of Λ Hypernuclei

  • The Contribution of the Three-Body Process in the Nonmesonic Weak Decay of Hypernuclei H. Bhang(Seoul National University)For KEK-PS E508 Collaboration

    FB09 Bonn, Germany Aug. 31-Sep. 05, 2009I. The Weak Decay Modes of Hypernuclei.II. n/p ratio puzzle and 3-body NMWD process.III. The Partial Decay widths of NMWD; 2N, n, p

  • Nonmesonic q~ 400 MeV/cI. The Decay Modes of Hypernucleitot(=1/)m

    nm- ( p- )o ( no )p ( p np )n ( n nn )Mesonic q~ 100 MeV/c2N (NN nNN)(1N)(2N)3-Body Process; Predicted theoretically(2N-NMWD)n/p puzzle

  • The Status of NMWD Study of hypernuclei I. Fundamental Motivation ; to study the elem. B-B Weak Interaction ; + N N + N (S=1 B-B Weak Interaction )- n/p and Ay have been mainly studied so far.

    Outstanding Issues ;- Decay widths; n, p 2N (3-body process)- Asymmetry;- I=1/2 rule in NMWD ;

  • n/p puzzle and the previous searches

  • E508 & KEK-PS K6 beamline and SKS 12C(+,K+), P+ =1.05 GeV/c SKS; 100msr & short flight path

  • Coincidence Measurement (KEK-PS E462/E508) Pair yields, Ynp and Ynn() meas. {Ynn(), Ynp()}/Nnm {Nnn(), Nnp()}

    Can distinguish back-to-back(bb) and non-bb kinematic events.

    Require back-to-back (cos

  • Test of Modified DEMONS Program for n Efficiency

  • Coincidence Yields (NN correlations) n/p = 0.510.130.05 M. Kim et al., PLB (06)Nnn/Nnp (bb) n/p Detection efficiency corrected. Normalized to unit NMWD. back-to-back(bb) ; cos < -0.7 FSI/3-B broaden the angular corr. Well agreed with Th. Ratios.n/p puzzle finally solved.Why the exp. n/p ratios have been so high?

  • Quenching in both p and n spectra from that of INC(1N).What would be the mechanism for the nucleon Quenching? FSI & 3-Body process. Both reduce the energy of emitted nucleons. QuenchingQuenching of Singles Yield

  • Missing momentum dist. - |p1+p2| p12Momentum sum distribution. Two groups? - low mom(~200 MeV/c); Essentially same as the bb kinematics events. - high mom(~500 MeV/c); Non-bb kinematics events and indicate a third party either via FSI or 3-B int. process.

  • Theo. Prediction of 3-body process (2N) of NMWD. Model for 2N-NMWD; NN nNN - Alberico-Ericson for Nuc. matter (91), and - Ramos-Oset extended to finite nuclei (94). - Recently Bauer and Garbarino; extensive calc. including complete set of mesons and NN pairs. 2N = 0.25 0.27 (12C)

  • Previous INC calculation and Quenching Overproduction

  • INC (IntraNuclear Cascade) calculation A nucleus as a local density Fermi gas with Woods-Saxon density dist. FSI is simulated as a cascade free NN scattering along with Fermi blocking. Density geometry parameters are adopted from scattering data. These parameters are fixed for the decay INC calc. In principle, the INC does not have fitting parameters.

    (p,p) Mass DependenceM. Kim, JKPS 46 (05) 805

  • In principle, INC model does not have fitting parameters. However, to reproduce FSI in NMWD, we used INC as a fitting function for scattering data by renormalizing the NNNN. Renormalization param., =1.09+-0.04, defines the experimental FSI. Then INC carry this exp. FSI to the emitted nucleons in NMWD INC and a renormalization parameter2=0.08(-109.3)2+1.04

  • Reproduction of the inelastic scatterings with =1.09

  • Three-Body Process (2N) and the quenching of yields Total sum of the yields under 300MeV/c is reproduce with the branching ratio 2N-NMWD of 0.29. b2N 2N/nm =0.290.13- 3-Body NMWD; Uniform phase space distribution

  • 2N agrees with the current theo. Prediction. n, p agree with those of the most extensive recent calculation. Errors are big, 20-45%. Experiment(J-PARC E18)

  • SummaryWe have measured the branching ratio of 3-Body NMWD of 12C, 0.290.13, for the first time.Combining with the nm, we obtained the widths n and p including 3-body NMWD. These results are very well agreed with the current 3-body model predictions. 4. However, the errors are big, 20-45% For accurate meas. J-PARC E18 ; 2N (3-body decay process), n ,p for 12C

  • KEK-PS E508 collaborationKEK, RIKEN, Seoul N.Univ., GSI,Tohoku Univ., Osaka Univ., Univ. Tokyo,Osaka Elec. Comm. Univ., Tokyo Inst. Tech.

    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, M. J. Kim, T. Maruta, Y. Miura, Y. Miyake, T. Nagae, M. Nakamura, S. N. Nakamura, H. Noumi, S. Okada, Y. Okatasu, H. Outa, H. Park,P. K. Saha, Y. Sato, M. Sekimoto, T. Takahashi, H. Tamura, K. Tanida, A. Toyoda, K.Tsukada, T. Watanabe, H. J. Yim

  • Extra

  • Units ; b2N is derived from the quenching of yields of low missing momentum which is of bb kinematics events. 2N agrees with the current theo. Prediction. n, p agree with those of the most extensive recent calculation. Errors are big, 20-50%. Experiment(J-PARC E18) ; Extensive study including the non-bb events, namely those of the high missing momentum. Partial decay widths of NMWD

  • Korea-Japan Collaboration1990~1991; Prof. Yamazaki and Prof. Nakai visited Korea and introduced N. Physics activity in Japan and the new KEK-PS program.1992 ; started the KOSEF-JSPS international collaboration programand participated the E140a experiment of Prof. Hashimoto.1993 ; proposed the lifetime measurement E307 in collaboration with Prof. Hashimoto. It was the lifetime and proton measurement of hypernuclei and found the saturation of the total decay width at around carbon. E369 ; Neutron measurement; Breakthrough of the n/p puzzle.E462/E508; First coincidence measurement of NMWD and solved the n/p puzzle problem.2006 ; JPARC P18; proposal for 3-body NMWD decay. 2007; Got 1st stage approval and we are now preparing for it.

  • The collaboration was very successful, I consider. It was fun and enjoyable, so I would like to thank all the collaborators. I am quite sure it to be continued and further blossomed in J-PARC collaboration experiments.

  • Thank you very much.

  • Decay Counter Setup (J-PARC E18) Covers ~50% solid angle; 2(solid angle)x3(beam)

  • Np/decayNp/nm ~0.4+nn+n+pn+pLifetime and Proton Measurement (E307)

  • Neutron Measurement (E369) Neutron spectra measured. Target; 12C, 51V and 89Y n- seperation by TOF

  • Nn =0.69Neutron Spectrum (E369)EfficiencyNp =0.40 Nn is compared with Np. Nn (> 40 MeV) = 0.69 while Np = 0.40 (E307)HYP03 Conf.

  • E307/E369 Experiment ; n / p (12C) = (0.45 ~0.51) 0.15(stat. only) Obtained almost model independent way Large sys. error due to nm is cancelled First exp result to show a significantly smaller ratio than unity. n/p ratioHowever, some ambiguities still exist due to Coincidence measurements 5He E462 12C E508Asymmetry issue: Serious inconsistency among nm for C. final state int. 2N induced NMWD.

  • Korea-Japan CollaborationIn retrospect, for me the collaboration was quite successful and

  • Asymmetry parameter of 11B, 12C

  • *Status of n/p and pnm Models explain n/p, but not apnm !!

    Serious inconsistency between theo. and exp. nm values.

  • + meson; Sasaki et al., PRC 71 035502 (05)

    +a1 meson; Itonaga et al. PRC 77 044605 (08)Most recent status of n/p and pnm

  • Summarising on the decay widths of NMWDNN Correlation data show two groups of missing momentum, low and high mom groups. The HM group tells the existence of many-body process.FSI calculation strongly indicates that the reason behind the n/p puzzle was the quenching of the nucleon yields in NMWD. The degree of the quenching is well explained simply by adopting the uniform phase space distribution of the 3-body process, but of the significant fraction of NMWD. In order to extract the most fundamental decay observables, n, p accurately, one has to determine 2N first. J-PARC (E18). The 2N is

  • Status of NMWD of hypernuclei Urgent problems to be solved ; - I=1/2 rule (I: 4He)- 3-body process of Weak Decay; Is there really such processes? How much contribution? Why 3-body effect is so strong that it is comparabe to 2-body effect? - Branching ratios of NMWD; It has been so long, but accurate branching ratios are not available yet. Since the contribution of 3-body process seems significant, we have to measure first of all.

    J-PARC E22J-PARC E18

  • N() = N0 ( 1 + Ay cos) = N0 ( 1 + p Pcos) (p; Asymmetry parameter) Ay = N(0) N(180) N(0) + N(180) Asymmetry measurement of decay proton

  • Previous situation of Asymmetry ParameterExclusive Coin. Exp. E462/E508 High Statistics Exclusive identification of pnp channel

  • Theory: - 0.6 ~ - 0.8 Asymmetry parameter of 5He 5He

  • For 2N-NMWD, we adopted the kinematics of uniform phase space sharing of 3 nucleons. Total yields in LM region is produced with b2N= 2N/nm = 0.2610.086.

  • I=1/2 rule and Nonmesonic Weak Decay of 4H and 4He.

  • For 2N-NMWD, we adopted the kinematics of uniform phase space sharing of 3 nucleons. In order to explain the quenching, 2N~0.4nm2N is extracted by fitting the Np+ Nn, Npn+Nnn (cos).Extraction of 2N.Some enhancements!!

  • Missing momentum dist. - |p1+p2| p12 - upper fig.; 12C - lower fig. ; 11BWe observe two groups; - low mom(~150 MeV/c); 1N NMWD? - high mom(~500 MeV/c); What is this high mom group?Momentum sum distribution.Prelimi