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Decay asymmetry in non-mesonic weak decay of light L hypernuclei

Oct./13/2006 HYP2006@Mainz Univ. Decay asymmetry in non-mesonic weak decay of light L hypernuclei. T.Maruta KEK, JSPS fellow. KEK-PS E462/E508 collaborations. L polarization in n( p + , K + ) L. 1.05GeV/ c p +. accepted. P. L. p /p. E278. θ. K +. p +. K + scattering angle( j K ).

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Decay asymmetry in non-mesonic weak decay of light L hypernuclei

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  1. Oct./13/2006 HYP2006@Mainz Univ. Decay asymmetry in non-mesonic weak decay of lightLhypernuclei T.Maruta KEK, JSPS fellow KEK-PS E462/E508 collaborations

  2. Lpolarizationinn(p+,K+)L 1.05GeV/cp+ accepted P L p/p E278 θ K+ p+ K+ scattering angle(jK) jK 1/2 N(q+(+j))×N(q-(-j)) R = Inlarge scattering angle, Lis much polarized. N(q+(-j))×N(q-(+j)) jK <0 jK p+ K+ θ p/p P L Asymmetry measurement of decay proton Asymmetry : Volume of the asymmetric emission from NMWD N(q) = N0(1 +Acosq) jK >0 Asymmetry =N0(1 +aPcosq) L Asymmetry parameter (R + 1) N(q+) A = R = , (R - 1) N(q-) Difference of acceptance & efficiency is canceled out !

  3. Importance ofaNM measurement p If assuming initial S state p : d K : f We can know the Interference between different Isospin and Parity states.

  4. Motivation Present status Previous experiments Theoretical prediction 5He : 0.24±0.22 L -0.6～-0.7 12C,11B : -0.9±0.3 OME Ex. p+K+DQ Ex. etc. L L Ajimura et al. The aim of E462/E508 experiment Precise measurement of Asymmetry parameter • high statistics • Reduction of Statistical error. • p-n coincidence measurement • Lp→np • measurements of 5He and 12C,11B in same setup • possible to compare them in low systematic error L L L

  5. L 6Li → 5He+p L Excitation spectra w/ coincident decay particles for 6Li L p++6Li → K++6Li L PID spectrum inclusive 4.0×104 w/ proton w/ pion pcontamination in p-gate Systematic error

  6. Null asymmetry test (p, pX)reaction : Only Strong Interaction p or p Asymmetry = 0expected Instrumental Asymmetry<0.3%

  7. Ap = ap hPL Ap: Asymmetry ofp ap: Asymmetry Parameter of mesonic decay (=-0.642±0.013) PL: Polarization of L h: Attenuation factor (Monte-Carlo simulation) We can obtainaNMwithout theoretical help. p Procedure for aNM calculation (5He) p L Estimated from mesonic decay ・Polarization ofL M ・Asymmetry Parameter of Proton p Ap = aNMhPL

  8. Asymmetry parameter of 5He Theory: - 0.6～- 0.7 5He L L statistical p contami aNM=0.08±0.08+0.08 -0.00 p

  9. L Coincidence p p p p n n n n n np coincidence analysis np opening angle 5He cosq<-0.8 NMWD cosq

  10. 11 LB +p Excitation spectra w/ coincident decay particles for 12C L Level scheme of 12C L 5.8×104 inclusive N,a decay LH p decay 11 C +L w/ proton LB 8.1MeV 11 6.3MeV w/ pion gdecay 2.5MeV depolarized effect 0.0MeV LC 12

  11. 2o 15o Polarization of L (12C,11B) L L Itonaga et al. Prog. of Theo. Phys. Supp. 117(1994)14 If assuming polarization is proportional to scattering angle. M1 transition reduces Polarization ofL

  12. statistical p contami aNM=-0.14±0.28+0.18 p E160 : - 0.9±0.3 Asymmetry parameter of 12C, 11B L L -0.00

  13. Theoretical models such as p+K reproduce Gn/Gp ratio, but predict large negative aNM. p+K+DQ p • p+K+s+DQ model reproduces both Gn/Gp ratio and aNM. p+K+s OME p+K+s+DQ Sasaki et al. PRC71 (2005) 035502 p+K (1) Large b(1S0→3P0) and f(3S0→3P1) amplitude (2) Violation of DI=1/2 rule considered p+2p/r+2p/s+w+K+rp/a1 Itonaga et al. OPE Comparison with recent results p-shell

  14. Summary • A series of experiments, E462 (5He) and E508 (12C, 11B) were carried out to measure aNM precisely. • We obtained nearly zero aNM’s (0.08±0.08+0.08, -0.14±0.28+0.18) in both nuclei. We don’t observe the difference in both reaction mechanism. • Recent theoretical calculation indicates the contribution of the initial state of 1S0. For more check, measurement of 4H is required at J-PARC. L L L p -0.00 -0.00 L

  15. Spare OHP’s

  16. previous experiment at BNL 6Li(K-,p-)6Li L Excitation spectra w/ coincident decay particles for 6Li L 6Li (6Li→5He+p) PID spectrum L L L inclusive 4.0×104 w/ proton w/ pion pcontamination in p-gate Systematic error

  17. Garbarino’s calculation (with FSI effect) Ep 30MeV -0.46 50MeV -0.52 70MeV -0.55 0.05±0.14+0.08 0.15±0.10+0.09 0.07±0.09+0.09 Proton Energy Dependence (5He) L Q/2 • Low energy region • Contamination of • FSI • 2N-induced Neutron Proton Threshold (Counts/5MeV) th -0.00 PRL94 (2005) 082501 -0.00 -0.00 5Heの結果におけるFSI等の効果は小さいと考えられる

  18. Production of polarized hypernuclei 1.05GeV/cp+beam is injected. E462/E508 experiments Distribution ofLpolarization in then(p+,K+)Lreaction. 1.05GeV/c p+ P L p/p θ K+ jK p+ E278 K+ scattering angle(jK) Inlarge scattering angle,Lis much polarized.

  19. ー : E462 ー: E278 : Motoba et al. NPA577 (1994) 293c Polarization of L Motoba et al. g.s.+4.5MeVex. state

  20. N N S W N p,K,s L One solution • + K + s + DQ Sasaki et al. PRC71 (2005)035502 • b(1S0→3P0)とf(3S0→3P1) amplitudeに影響を与える • DI = 3/2が大きく寄与する • 今回Gn/Gp ratioとaNMを高精度で測定したことにより、 こういう反応機構の必要性が認識された。 p

  21. Importance of asymmetry measurement If assuming initial S state (ApplyingDI=1/2 rule) We can know the Interference between states with different Isospin and Parity .

  22. Decay counter Setup π p n n K p (KEK-PS K6 & SKS) Decay arm Solid angle: 26% 9(T)+9(B)+8(S)% polarization axis Charged particle： ・TOF (T2→T3) ・tracking（PDC） Neutral particle： ・TOF (target→NT) ・T3 VETO N: 20cm×100cm×5cm T3: 10cm×100cm×2cm T2: 4cm×16cm×0.6cm

  23. Charged particle identification E VS. dE/dx PID1 T2 energy loss (MeVee) E VS. TOF TOF (1/b) Total E PID2 d TOF p PID2 p e dE/dx PID1 Total E (MeVee)

  24. p p Comparison with E160 E160 E508 dE/dx&Etot TOF&Etot range&Etot PID function w/proton w/pion w/proton Energy spectrum

  25. Proton asymmetry of 12C and 11B L L Excitation spectrum w/proton KEK E369 data Excitation spectrum of 12C is well known from previous experiment eliminate the contamination such as QF event inside the gate

  26. L Asymmetry of 5He spectra w/ proton w/ pion

  27. Asymmetry parameter of mesonic decay L → p- + p 1/2 s 0 1/2 l =0,1 wave function: -sinq cosq 1 Angular distribution of decay proton Asymmetry parameter S : 88%、P : 12% a = 0.64

  28. N N S W N p,K,s L aNM p One (Sasaki et al.) solution p Ex.+ K Ex. + s Ex+D.Q. Sasaki et al. PRC71 (2005)035502 Experimental value Gn/Gp ratio weak coupling constant ofs meson Both Gn/Gp and aNM are consistent with experimental value. p

  29. PID window PID2 ( TOF .vs. Etotal ) p gate p gate PID1 ( dE/dX .vs. Etotal ) (p+, pX) reaction p or p

  30. 8000 s ～340psec p 6000 4000 K 2000 0 -3 -2 -1 1 2 3 0 (ns) K+ p+ T1 target Identification of hypernuclear formation Good p/K/p separation Good p/K separation 0 200 400 600 800 1000 1200 (MeV/c2) -800 -600 -400 -200 200 0 (mm)

  31. L Neutron spectrum for 5He Theory : Garbarino et al. PRC69 (2004) 054603 Theoretical calc. Q / 2 = 76MeV No peakingat half of Q-value (76MeV)even 5ΛHe suggested larger contribution of LNN→NNN or FSI than theoretical prediction.

  32. np- & nn- angular distribution (5ΛHe) Back-to-back Back-to-back Gn/Gp ~ Nnn/ Nnp= 0.45±0.11±0.03 systematic error is mainly come from efficiency for neutron (6%) + acceptance(3%)

  33. 13 Coincidence Measurement (A=12) En +Ep n + p Counts En +En 12ΛC n + n Ep +Ep p + p qNN cos MeV Gn/Gp ~ Nnn/ Nnp= 0.51±0.13±0.05 Analysis detail on Kim’s Poster

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