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H. Bhang (Seoul National University) NP2007 at J-PARC June 01-02, 2007

Coincidence Measurement of the Weak Decay of 12 Λ C Hypernucleus and the Three-body Weak Decay Process. H. Bhang (Seoul National University) NP2007 at J-PARC June 01-02, 2007. I. Previous searches and Motivation (J-PARC E18) II. Yield Characteristics and How to extract 2N-NMWD.

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H. Bhang (Seoul National University) NP2007 at J-PARC June 01-02, 2007

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  1. Coincidence Measurement of the Weak Decay of 12ΛC Hypernucleus and the Three-body Weak Decay Process H. Bhang (Seoul National University) NP2007 at J-PARC June 01-02, 2007 I. Previous searches and Motivation (J-PARC E18) II. Yield Characteristics and How to extract 2N-NMWD. III. J-PARC E18 and Decay Counter Setup: - Efficiency and Solid angles, - Yield Estimation and Beam time. IV. Summary

  2. I. Decay Modes and Motivation Mesonic q~ 100 MeV/c Γπ- ( Λ pπ- ) Γπo ( Λ nπo ) Γm Γnm Γtot(=1/τ) Previous Searches Γp ( Λp  np ) Γn ( Λn  nn ) (1N) Nonmesonic q~ 400 MeV/c (2N) Γ2N (ΛNN nNN) 3-Body Process • Focus: • Baryon-Baryon Weak Interaction • Long standing puzzle on Γn/Γp. • 2N NMWD; Predicted theoretically, • but not exp. idendtified yet.

  3. Гn/Гp puzzle and the previous searches OPE Gn / Gp 1.5 0.5 1 0 1. Γn/Γp Puzzle : Γn/Γpexp>> Γn/Γpth(OPE) ~ 1 ~0.1 All these derived from p spectra 2. Recent Development of Γn/Γptheory : 0.3 ~ 0.7 K.Sasaki (Direct Quark), Nucl. Phys. A669 (2000) 371 D. Jido (Heavy Meson Exc), Nucl. Phys. A694 (2001) 525

  4. Coincidence Measurement (KEK-PS E462/E508) Ep π+ θ En K+ SKS π To exclude FSI effect and 3-body decay in Гn/Гpand to identify 2N channel,  Exclusive meas. of each decay channel.

  5. Singles spectra in NMWD Nn / Np (60<E<110MeV) ~2.17±0.15±0.16 Nn / Np (E>60MeV) ~2.00±0.09±0.14 Nn/Np ~ 2 Гn/Гp~1/2 Okada et al., PLB 597 (2004) 249

  6. Coincidence Yields (NN correlations) 12ΛC Nnn/Nnp Гn/Гp Gn/Gp= 0.51±0.13±0.0 M. Kim et al., PLB (’06) 5ΛHe Gn/Gp= 0.45±0.11±0.03 B.Kang et al., PRL 96 (’06)

  7. Quenching of SinglesYield INC(1N) INC(1N) • Quenching in both p and n spectra from that of INC. • What would be the mechanism for the nucleon Quenching? •  FSI & 3-Body process. • 3. FSI ; n & p are indistingushable (isospin indep.)  HE similarity. • LE behavior ; Cross over effect  LE enhancement in p expected. • 4. Instead, What observed  LE enhancement in n spec. • 5. What would be the source of the LE n enhancement???

  8. Theoretical Prediction of 3-body process (Γ2N) of NMWD. N π Λ Ramos-Oset Model ; •Absorption of virtual pion by 2p-2h states. • Λpπ- is dominant at the weak vertex and • Pions are absorbed dominantly on the pn pair. In the process 3 nucleons are emitted; 1p(LE) + 2n (HE) • Γ2N ~ 0.2 Γnm

  9. Enhancement of nn pair yields in the nbb region (12ΛC) 15 counts 8 counts • Enhancement of Nnn in nbb, over that of Nnp, by a factor, Rnn/Rnp~(2.30.93). •  Assign it to Г2N. • 2. Just Rough Estimation; • 1) Nnp(nbb)  all FSI eff. •  Same FSI on Nnn •  Г2N ~ The residual Nnn • after FSI sub. •  Г2N / ГNM~0.150.09± • 2) Similarly, • but using INC for FSI • Г2N/ ГNM~0.270.12 RNN=NNN(nbb)/NNN(bb); Ratio of N(nbb) to N(bb)

  10. Singles and Coin. Yields Reproduction with INC. For 2N-NMWD, we adopted the kinematics of uniform phase space sharing of 3 nucleons (Dalitz kinematics). In order to explain the quenching,  Г2N=0.4Гnm • Singles Quenching • LE n enhancement • Pair Quenching • are reasonably well reproduced.

  11. Tactics to extract 2N-NMWD 1. 2N and FSI events can not be seperated from each other kinematiclly, but their yield characteristics can be utilized to distinguish them. . 2. Our tactics to extract 2N NMWD is based on 1) Singles and pair quenching, 2) LE n enhancement, 3) Nnn(nbb) enhancement, ; Most direct evidence. 4) Energy sum correlation and 5) PP events for the experimental FSI information. 3. Direct evidence would be the Nnn enhancement in non-back-to-back (nbb) kinematic region, but the statistics are limited yet.

  12. Status of NMWD of Λ hypernuclei I. Main Issue ; B-B Weak Interaction ; Λ + N -> N + N (ΔS=1 B-B Weak Interaction ) - Γn/Γp (≡np ratio) and Ay have been mainly studied so far. II. urgent Issues to be solved ; - ΔI=1/2 rule - 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 its contribution. J-PARC E22 J-PARC E18

  13. II. Decay Counter Setup Basic concepts are based on the setup of E462/E508 expeiments. • CDC+T1(Timing for charged one)+T2(neutron) • Side veto to reject passing through ptls • Share most of the detection system with E22

  14. Detection Efficiency of nucleon pairs and Expected Yields pp np nn bb: back-to-back nbb: non-back-to-back

  15. Summary 1. Now the Гn/Гp puzzle problem solved finally, the measurement of 2N-NMWD, 3-body decay process, is most urgent before we determine the decay observables of NMWD. 2. The signatures of (2N)-NMWD processes were found both in the singles and coincidence data. All of them indicates fairly large Γ2N comparabel to Γ1N. 3. We still can not say much on each decay width of each channel of NMWD. It is because ot the large Γ2N and its large error bar. 4. We proposed the proposal P18 whose purposes are to determine accurately; 1) Γ2N : The strength of 3-body decay proces 2) Γn,Γp ; have to determine their magnitudes. 5. P18 naw got the phase-1 (physics) approval and became E18. We have to prepare for the phase-2 approval.

  16. J-PARC 50-GeV E18 collaboration KEK, RIKEN, Seoul Univ.,Tohoku Univ., Osaka Univ., Univ. Tokyo, Osaka Elec. Comm. Univ.G , Tokyo Inst. Tech., KRISS, Pusan N. Univ., Kyungbuk N. Univ. J.K. Ahn, K. Aoki, H. Bhang, S. Choi, T. Fukuda, O. Hashimoto, S. Kameoka, B. H. Kang, J. H. Kim, M. J. Kim, W. Kim, Y. Lee, 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. Tshoo, K.Tsukada, T. Watanabe, H. J. Yim. H. Bhang; bhang@snu.ac.kr H. Outa ; outa@riken.jp H. Park ; hyeonseo@kriss.re.kr

  17. Extra

  18. (3-Body)

  19. PID for neutral and charged particles Charged particle PID will be improved than that of E508 Essentially same as E508 LE particles; CDC + E HE particles; ΔE(0.6cm) + E(2cm)

  20. Proposal • Main Objects : • To measure the 3-body decay process, namely Γ2N, the 2-nucleon induced NMWD in 10% error level • To measure all decay widths of NMWDin 10% error level. • Reaction : 12C(π+,K+) at Pπ=1.05 GeV/c with 107π/spill. • Spectrometer & Detector : • SKS Kaon spectrometer; 100 mSr. • Coincidence Detectors;2π Sr • Yield Estimation and Expected Results: For 80 shifts, • Nnbb(nn) ~ 300 (23) • Nnbb(np) ~ 375 (12) • Nbb(pp) ~ 90 (8) • N(NNN) ~ (125) (5)

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