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First Exclusive Measurement of the Non-Mesonic Weak Deacay of 12  C

2004.06.08 dane2004. First Exclusive Measurement of the Non-Mesonic Weak Deacay of 12  C. Contents of talk n+n/n+p coincidence measurement  n / p ~ 0.40 ±0.09 (statistical error). Preliminary!!. Seoul national University. M.J.Kim.

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First Exclusive Measurement of the Non-Mesonic Weak Deacay of 12  C

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  1. 2004.06.08 dane2004 First ExclusiveMeasurement of the Non-Mesonic Weak Deacay of 12C Contents of talk n+n/n+p coincidence measurement n/p~ 0.40±0.09(statistical error) Preliminary!! Seoul national University M.J.Kim KEK-PS E462/E508 Collaboration

  2. E462/E508 Collaboration KEK, RIKEN, Seoul Univ., GSI, Tohoku Univ., Osaka Univ., Univ. Tokyo Osaka Elec. Comm. Univ. , Tokyo Inst. Tech. S. Ajimura, K. Aoki, A. Banu, H. Bhang, S.Shin,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, T. Nagae, 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

  3. Purpose Weak decay mode of  hypernucleus Mesonic q ~ 100MeV/c Γπ_(Λ→ ｐ + π－) Γπ0(Λ→ ｎ + π０ ) Γm 1/τHY =Γtot Γp(Λ+ ｐ→ ｎ + ｐ) Γn(Λ+ ｎ → ｎ + ｎ) Non Mesonic(NMWD) q ~ 400MeV/c Γnm Γ2N(ΛNN → NNN ) ? Direct determination of the ratio !!!! n/p

  4. Status of n/p of 12C(until recently) Theory 0.19 n/pexp >>n/pth n/p ratio puzzle! 0.27 0.20 0.83 0.12 0.10 Problems in Experiment 1)high threshold 2) Large error bar Problems in determination method of n/p ratio from data 1)model dependent 2) Effects of FSI and 2N process Experiment 1.33±1.21/0.81 1.87±0.59±0.32/1.00 * FSI: Final State Interaction

  5. Direct Measurement of the n /pratio Select ΛN→NN events without FSI and 2N process effect Top Detector Angular correlation ( back-to-back, cosq<-0.8 ) Energy correlation ( energy sum ~ Q value~150MeV ) Nucleon N  NMWD N → NN N Ynp=Nnpx npx nx px (1-RFSI)np Ynn=Nnnx nnx nx nx (1-RFSI)nn By charge symmetry (1-RFSI)np=(1-RFSI)nn ~ = 12LC g.s. Bottom Detector

  6. (KEK-PS K6 & SKS) SETUP Decay arm + Solid angle Neutral: 26.5% Charged : 10% NT p K+ n NT: 20cm×100cm×5cm T3: 10cm×100cm×2cm T2: 4cm×16cm×0.6cm Charged particle： ・TOF (T2→T3) ・tracking（PDC） Neutral particle： ・TOF (target→NT) ・T3 VETO Active Target beam

  7. Excitation energy spectra for 12C(p+,K+) 12LC g.s. quasi free inclusive 11C +  10.76MeV Proton decay 11 9.21MeV B+ p w/ proton 11 B 8.1 MeV  6.3 MeV w/ neutron w/ n+p 2.5 MeV 0.0 MeV 12 C w/ n+n  12 Level scheme of C  Excitation Energy(MeV) 11LB

  8. Particle identification Neutral particle Charged particle proton 5MeV< energy < 150MeV  Neutron  d Constant back ground → very small 1/ PID1 : total energy vs dE/dx PID2 : total energy vs TOF  (PID1+PID2) / Energy resolution ~8MeV at ~75MeV gated 12LC ground state

  9. Coincidence Measurement Angular Correlation Energy sum En +Ep cos θ＜－0.8 EN>30MeV n + p Number:109 cos θ＜－0.8 En +En EN>30MeV n + n Q value ~150 Number:33 MeV cos θ Estimated Contamination from - absorption

  10. Estimation of Nnp,Nnn (Nnn/Nnp = 0.40±0.09) MeasuredYnn,Ynp Simulated coincide efficiency EstimatedNnn,Nnp np(Ep,n=65MeV) Nnp=Ynp/np ~5677±572 cos θ＜－0.8 EN>30MeV Number:109 Event by event correction Nnn=Ynn/nn~2267±437 cos θ＜－0.8 nn(En,n=65MeV) EN>30MeV Number:33 Angular Correlation(cos ) θ

  11. Coincidence Measurement(E462/E508) Angular distribution Energy sum distribution Counts n + p s-shell 5 He  n + n Q value ~ 153MeV n + p p-shell 12 C  n + n cos θ Estimated Contamination from - absorption

  12. Results 5He (E462):0.45 ± 0.11 ± 0.04 (Final !!) 12C (E508):0.40 ± 0.09(statis.) (Preliminary !!) n/p 12 5 C He Noumi et al.   Szymanski et al. Sato et al.(1N) Sato et al.(1N+2N) Szymanski etal. Kim et al.(1N) OME OME,DQ OPE OPE E307 E307 E369 E508 E462 Theory(OPE) Various Experiments Theory(OME or DQ)

  13. Summary • The np- and nn-pairs from NMWD of 12C were observed successfully. The energy sum of back-to-back np- and nn- pairs are approximately equal to the Q-values(~150MeV) of the NMWD. N nN process were clearly identified !! • We got n/p ratio of 12C at cos <-0.8 and EN>30MeV . n/p ~ Nnn/Nnp ~ 0.40 ±0.09(statis. ) (Preliminary!! ) (expected systematic error ~ ±0.04) Consistent with recent theoretical calculations !!!! → θ

  14. Spare OHPS

  15. Experimental results n/p 1.33±1.21/0.81 1.87±0.59±0.32/1.00 0.87±0.09±0.21(1N) 0.60±0.11/0.09±0.23/0.21(1N +2N) 0.51±0.15(1N)

  16. Neutron and proton spectra from 12C Neutron N n,p/NMWD/10MeV Proton Nucleon energy (MeV)

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