Hypernuclear weak decay experiments at J-PARC 22. Sep. 2011 SNU 1 Hypernuclear weak decay experiments at J-PARC RIKEN　H. Outa J-PARC E18 and E22 experiments and more 　　　　　　(Stage2) (Stage1) Γπ_　(L→ ｐ + π－) Γπ0　　(L → ｎ + π０ ) Γp　(L +“ｐ”→ ｎ + ｐ) Γn　(L +“ｎ”→ ｎ + ｎ) Γ2N (ΛNN →NNN) Mesonic q～100MeV/c Non-Mesonic(NMWD) q～400MeV/c 1/tHY =Γtot Γm Γnm Weak decay mode of L hypernucleus Study of the mechanism of baryon-baryon weak interaction

Summary of KEK-PS NMWD experiments － Achievements － Open problems

[1] nn & np correlation KEK-PS E462/E508 NMWD : ΛN→NN n p L ２ [1] nn & np correlation KEK-PS E462/E508 Direct measurement of the Gn / Gp ratio NMWD : ΛN→NN Select LN→NN events w/o FSI effect & LNN→NNN. n p L Coincidence NMWD * cosθ<－0.8 * E(N1)+E(N2) cut 1) Angular correlation ( back-to-back, cosq<-0.8 ) 2) Energy correlation ( Q～E(N1)+E(N2) ～152MeV ) Select light hypernuclei to minimize FSI effect, 5LHe and 12LC

Gn / Gp ratio Λ N π Theo. N Λ 1 0.5 1.5 Gn / Gp Exp. S W ３ Λ N W S π One Pion Exchange (OPE) Theo. N Λ Direct Quark mechanism Meson Exchange π,K,η,ρ,ω… 1 0.5 1.5 Gn / Gp Previous exp. (at BNL) 0.93±0.55 (Szymanski et al.) for 5LHe Nnn / Nnp (5LHe)= 0.45±0.11±0.03 5LHe (E462) Kang et al. PRL 96 (2006) 062301 Exp. Γn / Γp (12LC)= 0.51±0.13±0.05 12LC (E508) Kim et al. PLB641 (2006) 28

[2] Decay asymmetry parameter of NMWD ４ [2] Decay asymmetry parameter of NMWD

Comparison with recent calculations ５ Comparison with recent calculations OME p+K,OME can reproduce Gn/Gp ratio but predict large negative aNM p+2p/r+2p/s+w+K+rp/a1 Calculation by Itonaga p+K+DQ p+K+s+DQ Gn/Gp and aNM can be reproduced by p+K+s+DQ model p+K+s p+K Sasaki et al. PRC71 (2005)035502 (1) Large b(1S0→3P0) and f(3S0→3P1) amplitude (2) Violation of ΔI=1/2 rule considered 最初に挙げた理論は、われわれに結果を再現しない。 で、最近出てきた理論はこうなりました。 ｋ OPE

[3] Nucleon Spectra FSI n p n p LN→nN n p LNN→nNN re-scattering ６ [3] Nucleon Spectra FSI re-scattering n p n p LN→nN n p LNN→nNN distribute low energy region up to Q/2 broad peak around Q/2 continuous distribution FSI σ(np)>σ(nn)=σ(np) A-dependence ∝ exp(- A1/3) エネルギー空間だとこういう差が出てくる １Nがフェルミ運動でぼけるが、Q/2の周りに分布するはずだ。 ２Nが3体のphase-spaceに一様に分布 counts Energy Energy spectra (image) Q/2

Single proton/neutron spectra from 5ΛHe and 12ΛC 7 Single proton/neutron spectra from 5ΛHe and 12ΛC Calculation by Garbarino et al. Nn～2Np S.Okada et al., PLB 597 (2004) 249

Singles and Coin. Yields w/ INC(1N+2N). M.Kim et al., Phys.Rev.Lett.103 182502,2009. ９ Γ2N/Γ1N=0.4 n p Singles Quenching LE n enhancement Pair Quenching are all reasonably reproduced.

ΛNN→NNN consideration ８ ΛNN→NNN consideration Garbarino ✔ Three nucleon coincidence w/ high statistics ✔ Low nucleon detection threshold Seen as…. n p Λn→nn like Λp→np like Λ n p W π- π0 4 1 n p

NMWD of Λ-hypernuclei - achievement and open problems - １０ NMWD of Λ-hypernuclei - achievement and open problems - ✔ Gn / Gp ～0.5 ✔ αNM～0 ✔ G２Ｎ / Gnmwd ～0.3 ? E18 ✔ Gnm (A～56）～1.2ΓΛ Meson Exchange mechanism Direct Quark mechanism × OPE ✔ Heavy meson exch./DQ N Λ Λ N π,K,η,ρ,ω… Spin/isospin dependence ?? × Hard to be explained w/ large Gn / Gp ✔ Some cancellation mechanism LNN→NNN (2N-induced process) Large contribution of 1S0 ΛN initial state?? Λ N W π

NMWD eｘｐｅｒｉｍｅｎｔs on A=4 hypernuclei E22 for 4ΛHe by Sagakuchi(Osaka) & Ajimura(RCNP) Stage-1 approved

NMWD of 4-, 5-body hypernuclei 1１ NMWD of 4-, 5-body hypernuclei allowed initial LN states n n p Λ p p n Λ p p n n Λ 0+ 0+ 0+ 0+ Ln→nn: 1S0, 3S1 1S0 1S0, 3S1 Lp→np: 1S0 1S0, 3S1 1S0, 3S1 initial final amplitude isospin parity 1S0 a 1 no 3P0 b yes 3S1 1S1 c 3D1 d 1P1 e 3P1 f assuming initial S state

Status of amplitude determination 1２ Status of amplitude determination Our prospects new constraint from 4LHe np-ratio better than 15% error Current status Constraint from 5LHe data other constraints are loose J-PARC E22

Setup upgrade in E18 KEK-12GeV PS E462/E508 J-PARC 50GeV E18 Wn=26 % 13 Setup upgrade in E18 KEK-12GeV PS E462/E508 J-PARC 50GeV E18 T4: 20 cm x 100 cm x 5cm T3: 10 cm x 100 cm x 2cm T2: 4 cm x 20 cm x 0.4 cm T4: 20 cm x 100 cm x 5cm T3: 10 cm x 100 cm x 2cm T2: 4 cm x 16 cm x 0.6 cm Wn=26 % Wp =10% Wn ~47 % Wp ~40%

Double coincidence eff. Simulation Study 1４ np enn enp nn beam p n E18 E18 qnp E508 E508 cosqnp cosqnn epp pp eNN E18 Double coincidence eff. at EN=75MeV → Much increased!!!!!!!! E18 pp np E508 nn cosq pp cosqNN

PRC 76,035511 (2007) Protons from 4ΛHe LN→nN n p counts Energy 15 PRC 76,035511 (2007) Protons from 4ΛHe counts Energy Energy spectra (image) Q/2 n p LN→nN

16 Opening angle EN1+EN2 p+n p+n n+n n+n ? PRC 76,035511 (2007)

By-product of E22 & Others ー Decay widths

Gp- and Gp 0 for 5LHe Gp0 Gp- GL GL Isle SG Isle SG 17 GL GL Gp- 0.322±0.018 GL Gp0 0.207±0.013 GL Isle SG Isle SG Now we obtained the pi- and pi0 decay width of 5LHe, using measured lifetime and the branching ratios. Here, we displays our result with previous data and theoretical calculation using Isle and SG potential. Our measurement drastically improved the accuracy compared to the previous data, and is in excellent agreement with theoretical calculation based on Isle potential. This clearly indicates the alpha-Lambda potential has repulsive core. Isle/SGのポテンシャルの絵を小さくでもみせたほうがよい。 Λ-nucleus potential with inner repulsive core can reproduce present experimental results Measured with much improved accuracy

4ΛHe/ 4ΛH: π-mesonic widths: １8 4ΛHe/ 4ΛH: π-mesonic widths: (calc. value – exp. value) / exp. error Calculations: T. Motoba, Nucl. Phys. A547 (1992) 115. I. Kumagai-Fuse et.al., Phys. Lett. B345 (1995) 386. ✔　Need to measure lifetime, Br(π-), Br(π0) ✔　NMWD widths ✔ Special interests on Br(π-)/Br(π0)

At J-PARC Remaining problems on NMWD to be solved at J-PARC 19 Remaining problems on NMWD to be solved at J-PARC ΛNN→NNN (E18) Spin/isospin structure and ΔI=1/2 rule at A=4 (E22) Γn/Γp ratios on 4ΛHe(E22) and 4ΛH must be the most important issue but the measurement might not be free from the effect of ΛNN→NNN (E18) If K1.1 beam line is ready and SKS moved to there in early stage, run E18 and/or E22 at K1.1 is possible 4. 20-30days DAQ @3-4×106 π＋　(1-2×1012 total π+) with SKS will improve accuracy of Γn/Γp & ΛNN→NNN related data by 5～10: also much improved accuracy on branching ratios and lifetimes will be obtained　　　 BG-level test of neutron counters at K1.8(or K1.1) needed

? COSY-13 (π,K) @J-PARC 2 weeks KEK-E307 19 Lifetime of very-heavy hypernuclei ? (J-PARC) COSY-13 (π,K) @J-PARC 2 weeks ? KEK-E307 49

Mass number dependence of ΓNM 24 Mass number dependence of ΓNM 42

23 Decay Widths