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Nonmesonic weak decay of 5 Λ He and 12 Λ C and the effect of FSI on its observables

Nonmesonic weak decay of 5 Λ He and 12 Λ C and the effect of FSI on its observables. H. Bhang for KEK-PS SKS collaboration (Seoul National University) Dafne04 Conf. on Physics at Meson Factories LNF, Frascati June 07~ 11, 2004. I. Issues / focus of NMWD II. Recent Experiments

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Nonmesonic weak decay of 5 Λ He and 12 Λ C and the effect of FSI on its observables

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  1. Nonmesonic weak decay of 5ΛHe and 12ΛC and the effect of FSI on its observables H. Bhang forKEK-PS SKS collaboration (Seoul National University) Dafne04 Conf. on Physics at Meson Factories LNF, Frascati June 07~ 11, 2004 I. Issues / focus of NMWD II. Recent Experiments III. Гn/Гp, FSI and 2N contribution.

  2. Weak Decay Modes of Λ Hypernuclei Mesonic q~ 100 MeV/c Γπ- ( Λ pπ- ) Γπo ( Λ nπo ) Γm Γnm Γtot(=1/τ) Γp ( Λp  np ) Γn ( Λn  nn ) Nonmesonic q~ 400 MeV/c (1N) (2N) Γ2N (ΛNN NNN) High momentum interaction Main focus of this talk

  3. Non-Mesonic Weak Decay (NMWD) & Issues • 1. B-B Weak Interaction ; • Λ + N -> N + N (ΔS=1 B-B Weak Interaction ) • 2. Long standing puzzle on : Γn/Γp(≡np ratio) • 3. 2N NMWD: Predicted to be a significant component of NMWD, though not experimentally identified yet. • 4. Asymmetry ;The relative phase concern of PC and PV part of NMWD interaction. • 5. Final State Interaction :It seems one of the important elements to understand NMWD.

  4. Status of Γn/Γp puzzle 1. Γn/Γp Puzzle : Γn/Γpexp>> Γn/Γpth(OPE) ~ 1 ~0.1 2. Recent Development of Γn/Γptheory : 0.3 ~ 0.7 3. Recent Exp. Development: p n p,n simultaneous p,n coinc. ~ 1.0 ~0.5 ~0.5 ~ 0.4

  5. Λ+nn+n Λ+pn+p Proton Energy spectrum Np/nm ~0.4 INC INC Np/decay Ramos et al. Sato et al., PRC submitted where 2N ; ΛNN  NNN.

  6. Neutron Spectrum Efficiency Nn=0.69 • n yield is directly comparedwith that of p. • 3. Simple number counting gives Np =0.40 PRC 68 (03) 065201 Λ+nn+n Λ+pn+p

  7. β=0.076 Correction for Cross over recoil effects - Assume1N process only ; rn + rp = 1. - The neutron (proton) number per NMWD Nn=Yn/NnmΩnεn = (2rn+rp)f+ rpg Np=Yp/NnmΩpεp = rpf+(2rn+rp)g, where f, g ; FSI effects. Γn/Γp= (0.45~0.51)+-0.15 - Obtained model independently assuming 1N process. - The INC β value is used only for second order correction.

  8. Гn/Гp ratio E307/E369 : Гn/Гp (12ΛC)|1N= (0.45 ~0.51)± 0.14 (stat. only) • Almost model independent. • This ratio agrees well with the most recent theoretical values (~.5) However, ambiguities due to • In order to resolve the difficulties, • Exclusive measurements • • 5ΛHe  E462 • • 12ΛC  E508 • final state int. • 2N induced NMWD.

  9. Setup E462/E508 (KEK-PS K6 beamline & SKS) Solid angle: 26% 9(T)+9(B)+8(S)% π p n K

  10. Neutron and Proton energy spectra of 5LHe and 12LC To avoid suffering from FSI effect & ΛNN→NNN, High energy threshold Nn / Np (60<E<110MeV) ～ 2.17±0.15±0.16 135MeV Nn / Np (E>60MeV) ～2.00±0.09±0.14 apply a simple relation Gn / Gp = (Nn / Np - 1) / 2 Gn / Gp～ 0.5

  11. Estimation of Nnn, Nnp (Nnn/Nnp=0.45±0.11±0.04) En,p>30MeV N(np-pair)/enp~ 4180 Cos(q)<-0.8 1000 N(n+p)=90( -1.34) measured n+p N(nn-pair)/enn~ 1956 N(n+n)=30(-4.38) measured n+n p- contamination -1 0 1 -1 0 1 -1 1 0 nn, np measured Angular correlation cos(q)

  12. Γn/Γp from Nn/Np & Nnn/Nnp Simple counting of singles yields of n,p and coincidence yeilds of nn, np pairs gives, Nn/Np = 2•Гn/Гp + 1, Nnn/Nnp ~ Гn/Гp, neglecting FSI and 2N. Γn/Γp(Nn/Np) 0.59 (5ΛHe), 0.5 (12ΛC), Γn/Γp(Nnn/Nnp) 0.45 (5ΛHe), 0.40 (12ΛC).

  13. Correction for Cross over recoil effects For the singles of E462/E508 5ΛHe (E462)  Γn/Γp(5ΛHe) = 0.61 ± 0.081 ± 0.082. 12ΛC(E508)Γn/Γp(12ΛC) = 0.58 ± 0.06 ± 0.08. Similiarly for the coincidence yields of 5ΛHe and 12ΛC (E462/E508), where β’ is reduced β due to the back-to-back selection. 5ΛHe (E462)  Γnn/Γnp(5ΛHe) = 0.43 ± 0.12 ± 0.044 12ΛC(E508)Γnn/Γnp(12ΛC) = 0.34 ± 0.13 ± 0.05.

  14. Γn/Γp Status OME, DQ model OPE Gn / Gp 1.5 0.5 1 0 Exp. Singles 5ΛHe : 0.61±0.081±0.082 (E462) 12ΛC : 0.58±0.06±0.08(E508) : (0.45~0.51)±0.15 (E307/E369) Coincidence 5ΛHe : 0.43 ±0.12 ±0.044±(E462) 12ΛC : 0.34 ±0.13 ±0.05 (E508)

  15. Summary • I have discussed the recent experimental results on NMWD of Λhypernuclei and the effects of FSI on theΓn/Γp. • A series of experiments have been done at KEK-PS, • the decay particle spectra of n and p (Nn, Np) and • the exclusive coincidence pair yields (Nnn, Nnp) of NMWD • 3. The ratios of singles yields of n/p and coincidence yeilds of nn/np gives Γn/Γp values which well supports the recent theoretical ratios. • 4. The difference of Γn/Γp values from singles yields of n/p and coincidence yeilds of nn/np is interpretted as 2N contribution. This probably is the first experimental indication of 2N process. • It is expected that the 2N contribution now can be extracted from the coincidence data.

  16. KEK-PS E462/508 collaboration KEK, RIKEN, Seoul Univ., GSI, Tohoku Univ., Osaka Univ., Univ. Tokyo Osaka Elec. Comm. Univ.G , 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

  17. Extra OHPs

  18. Neutron and Proton energy spectra of 5LHe and 12LC To avoid suffering from FSI effect & ΛNN→NNN, High energy threshold Nn / Np (60<E<110MeV) ～ 2.17±0.15±0.16 135MeV 5LHe → n + a : Q～135MeV (rate : 0.049±0.01Gp-) apply upper energy limit of 110MeV ! Nn / Np (E>60MeV) ～2.00±0.09±0.14 apply a simple relation Gn / Gp = (Nn / Np - 1) / 2 Gn / Gp～ 0.5 Corrected proton energy loss inside the target !!

  19. Neutron Neutron Proton Proton Neutron and Proton Energy spectra of5ΛHe and 12ΛC Nn / Np (E>60MeV) ~ 2.17±0.15±0.16 Nn / Np (E>60MeV) ~2.00±0.09±0.14

  20. Correction for Cross over recoil effects For the singles of E462/E508 β=0.041 where α=2.00 (5ΛHe), 2.17 (12ΛC) 5ΛHe (E462)  Γn/Γp(5ΛHe) = 0.61 ± 0.081 ± 0.082. 12ΛC(E508)Γn/Γp(12ΛC) = 0.58 ± 0.06 ± 0.08.

  21. Correction for Cross over recoil effects Similiarly for the coincidence yields of 5ΛHe and 12ΛC (E462/E508), where β’ is reduce β due to the back-to-back selection. 5ΛHe (E462)  Γnn/Γnp(5ΛHe) = 0.43 ± 0.12 ± 0.044 12ΛC(E508)Γnn/Γnp(12ΛC) = 0.34 ± 0.13 ± 0.05.

  22. Correction for Cross over recoil effects Similiarly for the coincidence yields of 5ΛHe and 12ΛC (E462/E508), where β’ is reduce β due to the back-to-back selection. 5ΛHe (E462)  Γnn/Γnp(5ΛHe) = 0.43 ± 0.12 ± 0.044 12ΛC(E508)Γnn/Γnp(12ΛC) = 0.34 ± 0.13 ± 0.05.

  23. Γn/Γp Status OME, DQ model OPE Gn / Gp 1.5 0.5 1 0 Exp. Singles 5ΛHe : 0.61±0.081±0.082 (E462) 12ΛC : 0.58±0.06±0.08(E508) : (0.45~0.51)±0.15 (E307/E369) Coincidence 5ΛHe : 0.45±0.11±0.04 (E462) 12ΛC : 0.40±0.09 (E508)

  24. CONTENTS I. Issues / focus ofNonmesonic Weak Decay (NMWD) II. Recent Experiments 1. Singles meas. ; Nn and Np; (KEK-PS E307 /E369) 2. Coincidence meas. : Nnn and Nnp(E462/E508) III. Гn/Гp and Final State Interaction 1. Effects of FSI onГn/Гp 2. 2N signature IV. Summary

  25. Taking the ratios of singles yields of n/p and coincidence yeilds of nn/np give Γn/Γp different values whose differce is interpreted as 2N contribution, Γn/Γp (Nn/Np)  0.61(5He), 0.58(12C), Γn/Γp (Nnn/Nnp)  0.43(5He), 0.34(12C). 4. Showed that 2N component can be resolved from coincidence data. For the extraction of 2N contribution, one need FSI model calculation but only for the second order effect. 5. Pinning the The direct comparison of the spectra gave the Γn/Γp ratio close to 0.5. The coincidence exclusive measurements of NMWD produced the results on NMWD quite free from FSI and 2N contribution. The results show the Γn/Γp ratio ~0.4. 5. As long as Γn/Γp ratio concerned, the experimental and theoretical ratios now well agree to each other. However, αnm remains inconsistent between those of experiment and theory.

  26. INC calculation • Therefore, • Where • Γn/Γp= (0.45~0.51)±0.15 • Obtained model independently assuming 1N process and fn=fp. • The INC β value is used only for second order correction. 0.076 HYP03 Conf.

  27. Theory: - 0.6～- 0.7 Asymmetry parameter of 5ΛHe (E462) Preliminary p contami statistical +0.08 aNM=0.07±0.08 p -0.00

  28. Red : 11B : aNM = 0.11 ± 0.44 L Theory: - 0.6～- 0.7 Blue : 12C : aNM = -0.44 ± 0.32 L Asymmetry parameter of 12ΛC,11ΛB (E508) p contami Preliminary statistical +0.08 aNM=-0.24±0.26 p +0.00

  29. Current Status of Γn/Γp Theory Experiment HYP03 Conf.

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