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Coincidence Measurement of the Non-Mesonic Weak Deacay of 12  C

PANIC05. Coincidence Measurement of the Non-Mesonic Weak Deacay of 12  C. Mijung Kim. Seoul National University. KEK-PS E462/E508 Collaboration. Purpose. Weak decay mode of  hypernucleus. Mesonic q ~ 100MeV/c. G π _ (Λ→ ｐ + π － ) G π 0 (Λ→ ｎ + π ０ ). G m. 1/τ HY =Γ tot.

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Coincidence Measurement of the Non-Mesonic Weak Deacay of 12  C

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  1. PANIC05 CoincidenceMeasurement of the Non-Mesonic Weak Deacay of 12C Mijung Kim Seoul National University KEK-PS E462/E508 Collaboration

  2. Purpose Weak decay mode of  hypernucleus Mesonic q ~ 100MeV/c Gπ_(Λ→ ｐ + π－) Gπ0(Λ→ ｎ + π０ ) Gm 1/τHY =Γtot Gp(Λ+ ｐ→ ｎ + ｐ) Gn(Λ+ ｎ → ｎ + ｎ) Non Mesonic q ~ 400MeV/c Gnm G2N (ΛNN →NNN) ? Determination of the Gn/Gp ratio!! Gn/Gpratiois very impotant quantity to understand non-mesonic weak decay mechanism

  3. Status of n/p ratio of 12C(until recently) Theory n/pexp>>n/pth n/p ratio puzzle! 0.19 0.20 0.12 0.10 To resolve this problem there have been many efforts both theoretical and experimental side !! Experiment 1.33±1.21/0.81 1.87±0.59 ±0.32/1.00 *OPE: One Pion Exchange Model

  4. Theoretical Side efforts

  5. Experimental Side efforts Gp(Λ+“ｐ”→ ｎ + ｐ) Gn(Λ+“ｎ”→ ｎ + ｎ) Gn/Gp Using Proton spectra and INC calculation Noumi et al. Using Proton and Neutron spectra measured in different experiment Statisticalerror only Sato et al.(1N) Sato et al.(1N+2N) Szymanski et al. Kim et al.(1N) Using Proton and Neutron measured simultaneously Various Experiments Still there are ambiguities due to FSI and possible 2N inducedprocess!!!! *INC: IntraNuclear Cascade *FSI:Final State Interaction

  6. Determination of the n /p ratio(Newapproach!) Select ΛN NN events with reduced FSI/2N effects Top Detector Nucleon N  Angular correlation ( back-to-back) Energy correlation ( energy sum ~ Q value~150MeV) q NMWD N→NN N Bottom Detector Nnn/Nnp n/p Gp(Λ+“ｐ”→ ｎ + ｐ) Gn(Λ+“ｎ”→ ｎ + ｎ) By requiring back-to-back condition and considering FSI effect

  7. (KEK-PS K6 & SKS) Decay arm SETUP Solid angle Neutral: 26.5% Charged : 10% + T4 K+ p q T4: 20 cmx 100 cmx 5cm T3: 10 cmx 100 cmx 2cm T2: 4 cmx 16 cm x 0.6 cm n Target beam

  8. Particles identification Neutral Charged PID1 : total energy vs dE/dx PID2 : total energy vs TOF gated 12LC ground state

  9. Excitation energy spectra for 12C(p+,K+)12C 11LB 12ΛC g.s. inclusive Counts w/ p w/ n w/ n+p w/ n+n Excitation Energy(MeV)

  10. Coincidence Measurement n + p n + n YNN/NMWD NNN/NMWD Q-value Q-value Count/10MeV ~150MeV ~150MeV

  11. Coincidence Measurement En +Ep n + p Counts En +En n + n Ep +Ep p + p qNN cos MeV

  12. Uniform components subtraction Nnp/NMWD Nnn /NMWD Uniform components Uniform components Cos np Cos nn

  13. FSI effectsconsideration using pp-pairs rn,pfraction ratio of theneutron and proton induced channels. fn,pis reduction factor due to FSI. gn,pis cross over influx of neutron(proton) from proton(neutron) due to FSI. p,q,q’are angular acceptance factor. , , ,

  14. Coincidence Measurement(E462/E508) Energy sum distribution Estimated contamination from Pair numbers/NMWD n + p n + n

  15. Preliminary!!! stat. error only Indicates NMWD mechanism of s- and p-shell hypernuclei rather similar!!

  16. Summary We have measured and identified and NMWD modesof in the first coincidence measurement by requiring the back-to-back correlation of emitted nucleon pairs which is the signature of two-body decay. We have obtained the Gn/Gp ratio from np and nn pair numbers whose events satisfy the condition of the back-to-back angular kinematics and whose FSI effects have been self corrected with the pp pair events simultaneously measured . The obtained preliminaryGn/Gp ratio, , is agree well with recent theoretical results calculated based on OME models finally resolving the long standing Gn/Gp ratio puzzle unambiguouslyand quite close to that of indicating the decay mechanism of s-shell( ) and p-shell( ) hypernuclei are rather similar.

  17. Spare PPT

  18. 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)

  19. 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

  20. Background/Contamination estimation Over bound g.s Quasi free np pair inclusive w/ n+p nn pair w/ n+n cos NN Excitation energy(MeV) From absorption ( ) , Yieldsofnp pairs Yieldsofnn pairs

  21. Efficiency/Acceptance simulation 2MeVee 3MeVee 4MeVee 5MeVee Simulated neutron detection efficiency Raw neutron spectra SimulatedProton acceptance including detection efficiency Corrected spectra Threshold control is worked well.

  22. Singles Spectra

  23. Efficiency and acceptance simulation(coincidence measurement) np pair nn pair At E=65MeV 0.18x0.3x0.3=0.0162 0.1x0.3x0.93=0.028

  24. Estimation of Y’np,Y’nn Simulated coincidence acceptance including efficiency MeasuredYnp,Ynn EstimatedY’np,Y’nn Counts Y’np=Ynp/np~6411±641 cos θ＜－0.7 EN>30MeV Number:116 Event by event correction Y’nn=Ynn/nn~3827±666 cos θ＜－0.7 EN>30MeV Number:43 Angular Correlation(cos ) qNN

  25. Mass Dependence of Gn/Gp n/p 1N 1N 1N+2N 1N+2N Mass number

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