1. Hypernuclear weak decay experiments at J-PARC
22. Sep 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

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

3. [1] nn & np correlation KEK-PS E462/E508 NMWD : ΛN→NN n p L２
[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

4. Gn / Gp ratio Λ N π Theo. N Λ 1 0.5 1.5 Gn / Gp Exp. S W３ 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)
Exp.
Γn / Γp (12LC)= 0.51±0.13±0.05
12LC (E508)
Kim et al. PLB641 (2006) 28

5. [2] Decay asymmetry parameter of NMWD４
[2] Decay asymmetry parameter of NMWD

6. Comparison with recent calculations５
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

7. [3] Nucleon Spectra FSI n p n p LN→nN n p LNN→nNN re-scattering６
[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

8. Single proton/neutron spectra from 5ΛHe and 12ΛC7
Single proton/neutron spectra from 5ΛHe and 12ΛC
Calculation by
Garbarino et al.
Nn～2Np
S.Okada et al.,
PLB 597 (2004) 249

9. 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.

10. ΛNN→NNN consideration８
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

11. 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

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

13. NMWD of 4-, 5-body hypernuclei1１
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

14. Status of amplitude determination1２
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

15. 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%

16. 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

17. PRC 76,035511 (2007) Protons from 4ΛHe LN→nN n p counts Energy15
PRC 76, (2007)
Protons from
4ΛHe
counts
Energy
Energy spectra (image)
Q/2 n p
LN→nN

18. 16
Opening angle
EN1+EN2
p+n
p+n
n+n
n+n ?
PRC 76, (2007)

19. By-product of E22 &
Others
ー Decay widths

20. Gp- and Gp 0 for 5LHe Gp0 Gp- GL GL Isle SG Isle SG17 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

21. 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)

22. At J-PARC Remaining problems on NMWD to be solved at J-PARC19
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
days 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

23. ? COSY-13 (π,K) @J-PARC 2 weeks KEK-E30719
Lifetime of very-heavy hypernuclei ? (J-PARC)
COSY-13
(π,K)
@J-PARC
2 weeks ?
KEK-E307 49

24. Mass number dependence of ΓNM24
Mass number dependence of ΓNM 42

25. 23
Decay Widths