Decay asymmetry in non-mesonic weak decay of light  hypernuclei T.Maruta KEK, JSPS fellow Oct./13/2006 Univ. KEK-PS E462/E508 collaborations

2 Asymmetry measurement of decay proton Asymmetry : Volume of the asymmetric emission from NMWD Difference of acceptance & efficiency is canceled out !  K >0 ++ K+K+  /p KK   P  K <0 ++ K+K+ /p/p KK   P N(  ) = N 0 (1 + Acos  )  Asymmetry A = (R - 1) (R + 1) R = N(-)N(-) N(+)N(+), Asymmetry parameter = N 0 (1 +  Pcos  ) R = N(  + (-  ))×N(  - (+  )) N(  + (+  ))×N(  - (-  )) 1/2  polarization in n(  +,K + )  K + scattering angle(  K ) 1.05GeV/c  + E278 In large scattering angle,  is much polarized. accepted

3 If assuming initial S state We can know the Interference between different Isospin and Parity states. Importance of  NM measurement State ParityIsospin Amplitude InitialFinalI f z = 0I f z = -1 1S01S0 1S01S0 PC1 3P03P0 PV1 3S13S1 3S13S1 PC0 ー 3D13D1 0 ー 1P11P1 PV0 ー 3P13P1 1  : d K : f p

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

5 Excitation spectra w/ coincident decay particles for 6 Li inclusive w/ proton w/ pion  4.0×10 4  contamination in p-gate Systematic error PID spectrum 6 Li → 5 He+p    Li → K Li

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

7 Procedure for  NM calculation ( 5 He) A  =    P  A  : Asymmetry of    : Asymmetry Parameter of mesonic decay (=-0.642±0.013) P   Polarization of   : Attenuation factor (Monte-Carlo simulation) ・ Polarization of  ・ Asymmetry Parameter of Proton A p =  NM  P  p p Estimated from mesonic decay We can obtain  NM without theoretical help. p  M

8 Theory: ～ Asymmetry parameter of 5 He   NM =0.08± p statistical  contami He 

9 np coincidence analysis n p n p  n n p n p Coincidence NMWD np opening angle cos  cos  < He

10 Excitation spectra w/ coincident decay particles for 12 C   B + p 11 C +  11 CC 12 p decay BB MeV 6.3MeV 2.5MeV 8.1MeV  decay depolarized effect inclusive w/ proton w/ pion 5.8×10 4 Level scheme of 12 C  LH N,  decay

11 Polarization of  ( 12 C, 11 B) Itonaga et al. Prog. of Theo. Phys. Supp. 117(1994)14 M1 transition reduces Polarization of  2o2o 15 o If assuming polarization is proportional to scattering angle. 

12 Asymmetry parameter of 12 C, 11 B   NM =-0.14± p statistical  contami E160 : - 0.9±0.3

13 Comparison with recent results  +2  /  +2  /  +  +K+  /a 1 Itonaga et al. OPE  +K+DQ  +K OME p Theoretical models such as  +K reproduce  n /  p ratio, but predict large negative  NM.  +K+   +K+  +DQ  +K+  +DQ model reproduces both  n /  p ratio and  NM. p-shell Sasaki et al. PRC71 (2005) (1) Large b( 1 S 0 → 3 P 0 ) and f( 3 S 0 → 3 P 1 ) amplitude (2) Violation of  I=1/2 rule considered

14 Summary A series of experiments, E462 ( 5 He) and E508 ( 12 C, 11 B) were carried out to measure  NM precisely. We obtained nearly zero  NM ’s (0.08± , ± ) in both nuclei. We don’t observe the difference in both reaction mechanism. Recent theoretical calculation indicates the contribution of the initial state of 1 S 0. For more check, measurement of 4 H is required at J-PARC.   p 

15 Spare OHP’s

16 Excitation spectra w/ coincident decay particles for 6 Li inclusive w/ proton w/ pion 6 Li ( 6 Li→ 5 He+p)   4.0×10 4  contamination in p-gate Systematic error PID spectrum previous experiment at BNL 6 Li(K -,  - ) 6 Li 

17 Proton Energy Dependence ( 5 He) Proton Threshold (Counts/5MeV) 0.07± ± ± Q/2 Low energy region Contamination of  FSI  2N-induced 5 He の結果における FSI 等の効果は小さいと考えられる Neutron E p 30MeV MeV MeV Garbarino’s calculation (with FSI effect) PRL94 (2005) th 

18 Production of polarized hypernuclei E462/E508 experiments 1.05GeV/c  + beam is injected. Distribution of  polarization in the n(  +,K + )  reaction. K + scattering angle(  K ) 1.05GeV/c  + In large scattering angle,  is much polarized. P ++ K+K+  /p KK   E278

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

20 One solution  + K +  + DQ Sasaki et al. PRC71 (2005)  N NN W S ,K,,K,  b( 1 S 0 → 3 P 0 ) と f( 3 S 0 → 3 P 1 ) amplitude に影響を与える   I = 3/2 が大きく寄与する  今回  n /  p ratio と  NM 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 Initial stateFinal stateAmplitudeIsospinParity 1S01S0 1S01S0 a1No 3P03P0 b1Yes 3S13S1 3S13S1 c0No 3D13D1 d0 1P11P1 e0Yes 3P13P1 f1 If assuming initial S state We can know the Interference between states with different Isospin and Parity. (Applying  I=1/2 rule) Importance of asymmetry measurement

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

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

24 Comparison with E160 PID function Energy spectrum p  E160 E508 w/proton w/pion range&E tot dE/dx&E tot TOF&E tot

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

26 Asymmetry of 5 He spectra w/ protonw/ pion 

27 Asymmetry parameter of mesonic decay  →  - + p s 1/2 0 l =0,1 wave function: Angular distribution of decay proton 1 -sin  cos  Asymmetry parameter S : 88% 、 P : 12%  = 0.64

28 One (Sasaki et al.) solution  Ex.+ K Ex. +  Ex+D.Q.  n /  p ratio  NM p weak coupling constant of  meson Sasaki et al. PRC71 (2005) Both  n /  p and  NM are consistent with experimental value.  N NN W S ,K,,K, p Experimental value

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

30 Identification of hypernuclear formation K+K+ ++ T1 target  K  ～ 340psec (ns) (MeV/c 2 ) (mm) Good  /K separation Good  /K/p separation

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

32 np- & nn- angular distribution ( 5 Λ He)  n  p  nn /  np = 0.45±0.11±0.03 systematic error is mainly come from efficiency for neutron (6%) + acceptance(3%) Back-to-back

33 Coincidence Measurement (A=12) cos n + p n + n p + p E n + E p E n + E n E p + E p MeV  NN Counts 12 Λ C  n  p  nn /  np = 0.51±0.13±0.05 Analysis detail on Kim’s Poster 13