1 / 33

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 ).

ghalib
Download Presentation

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

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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

More Related