June 7-8, 2004
Seminar Hall, Bldg.4 KEK

KEK-PS External Review 2004
E438/E521
H. Noumi (KEK) for E438/E521

1. Introduction (p2~4)
2. E438 (p5~12)
3. E521 (p13~19)
4. to J-PARC (p20)1Importance of Hypernuclear Studies⇒ In order to reveal the Baryon-Baryon Interaction
System ⇒Two body

Theor. ⇒Few-body Calc.
OBEP, QM ⇔ G-Matrix ⇔Averaged Potential

Exp. ⇒Three body

Many body

YN scat’ng
Hypernuclei

2

Relative Fraction

E438: Study of the Σ-Nucleus Potential??Repulsive/Attractive? How Absorptive?
E521: Prod. of the neutron-rich Λ hypernuclei
Doorway to study the Λn Int.
the Coherent ΛΝ−ΣΝ coupling

Roles of Hyperons
in Neutron Star CoresNormalVΛ ~ VΣ

based on the YN/YY int.
from hypernuclei

Λ Σ−Maximal Mass<1.44MsolarVΣ : repulsive
No Sigma Appears
S. Balberg and A. Gal, NPA625(1997)435

Baryon Density (fm-3)

3

Role of the ΛN-ΣN coupling in Neutron Star Cores
S.Shinmura, K. S. Myint, T. Harada, and Y. Akaishi, J. Phys. G28(2002)L1coherent Λ→Σ
w/o exciting N(b)~(d)…
No effect in T=0Single-particle Λ potential in neutron matter (T=∞)
p=0% without coherent
p=10% ΛN-ΣN coupling
p=20%
p=20% with coherent
p=10% ΛN-ΣN coupling
p=0%PΣ0 increases with ρΝ 4

E438

Papers: published in PRL89(2002)072301
5submitted to PRC/nucl-ex 0405031

E438: Study of Σ-nucleus potential
by the (π-,K+) reaction on heavy nuclei
No Σ-hypernuclear bound states, but 4ΣHeUΣ = VΣ + i WΣ++ Aπ-K+X

Σ-Σ-ΛΣ-ΣΣ-

Inclusive spectrum tells the Σ potential…

6Inclusive (π-,K+) spectra at pbeam=1.2 GeV/c on CH2, Si, Ni, In and Bi
were measured at KEK-PS K6 with SKS in Oct. & Dec., 1999.
○Energy Resolutions
3.3~5.2 MeV (depend on tTGT)
maintain a sensitivity to WΣ .
○Energy/Cross Section Scales
calibrated by p(π-,K+)Σ- .
○Large Solid Angle
Wide Mom. Acceptancecovered by SKS.
Kaon-ID

7

Energy Scale
Energy Resolution

Cross Section Scale
Angular Dist. of the p(π-,K+)Σ- Reaction

3.31±0.33 MeV/c2

TargetSetupandZ-VertexDistributionπ-K+CH2Si250mmPresent Data
Previous Data @ 1.225 GeV/c(Curves: Error Boundary fromthe Legendre Poly. Fitting)PR 183(1969)1142
8

Measured Inclusive (π-,K+) Spectra on C, Si, Ni, In, & Bi
P. K. Saha et al., nucl-ex0405031/submitted to PRC
P. K. Saha, PhD thesis, KEK-Rep.2001-17○ Similar Shape○ No peak in -BΣ- <0 MeV○ Maximum @ -BΣ- >120 MeV

9Compared with DWIA Cal.
- Fitting Results χ2 dist.
(dof=56)

V0Σ dependence

W0Σ dependence

W.S. Potential Params
UΣUSiz(fm)0.67

0.537c(fm)

3.3

3.82

V0(MeV)-54.5
10

DWIA application to…

Bi (π-,K+)Ni, In, Bi(π-,K+)w/ (V0Σ, W0Σ) = (90 MeV, -40 MeV)
12C (π+,K+)

Cross Section (µb/sr/MeV)at θ K = 6oΚ2opπ=1.2 GeV/c

VΛ = −30 MeV

VΛ = 0 MeV

In (π-,K+)Ni (π-,K+)
Data from E521
11−ΒΛ(MeV)Concluding Remarks of E438
1. Inclusive (π-,K+) spectra on CH2, Si, Ni, In, & Bi were
measured with a good resolution (3~5 MeV in FWHM).
1.1 The measured spectra show a similar shape.
1.2 No peak structure in the bound region
1.3 The maximum at -BΣ- >120 MeV
2. The measured spectra on Si, Ni, In, & Bi were comparedto calculated ones within the framework of the DWIA.
2.1 A repulsive Σ−-nucleus potential with a non-zero sizeof the imaginary part was required to reproduce themeasured (π-,K+) spectra in shape.
2.2 This framework was successfully applied
to reproduce the (π+,K+) spectrum on C.
12

E521
Draft: preparation for publication

13

E521: Production of neutron-rich Λ hypernuclei
by the (π-,K+) double-charge-exchange reaction
A pilot experiment for spectroscopic studies of
the neutron-rich Λ hypernuclei via the (π-,K+) reaction
Production cross section/ Background (sensitivity)⇒ Understanding of the Reaction Mechanism
If it is promising,one can study…

Akaishi et al.
PRL 84(2000)3539

the Λn interaction
the Coherent
Λ−Σ coupling… exploring largely
neutron-excess
Λ hypernuclei
14

Superheavy hydrogen
5H

1.7

12-(MeV)-12.093H + 2n + Λ-4.4 MeV

0.0-12.17

rce
ΛNN fo-12.110.21
MeV2-γ1--12.28

D2 int.

ΛNNforce4
Λ H + 2n-1.4 MeV-2.04(PcohΣ=0.31%)

10ΛLi-4.1

6Li ( π-, K+)

6
ΛH“Hyperheavy hydrogen”

15

Reaction mechanism and the theoretical calculation
Tretyakova, Akaishi et al.

1. Single-step process:By the π−p -> Σ−Κ+ via
a small admixture of theΣ− state due to theΣ−p <->Λn coupling.

Cross Section (µb/sr)

80
70

10B(π−,Κ+)10Li
Λ60
50
4030
20
0.9 0.95

2. Two-step process:
π−p−>Κ0Λ ; Κ0p−>Κ+nπ−p−>π0n ; π0p−>Κ+Λ

1

1.05 1.1 1.15 1.2 1.25 1.3

Beam Momentum (GeV/c)

π−p−>Σ−Κ+ ; Σ−p−>Λ+n16

(counts/2MeV)

Experiemntal Results○ Background-Free○ 10ΛLi Observed Clearly

42610B(π−,Κ+)@1.2 GeV/c

504030(nb/sr/2MeV)(nb/sr/2MeV)

60@1.05 GeV/c

60-507010B(π−,Κ+)8050100 150
Λ Binding Energy[MeV]

Close-up

5432201100-50 -25 025 50 75 100 125 150

Λ Binding Energy [MeV]

0-40-2002040 17

Λ Binding Energy [MeV]Ratio of the Λ production cross section(π−,Κ+) to (π+,Κ+)Beam mom. Target Reaction Cross section(µb/sr) Ratio(GeV/c)-15<-BΛ<0.
1.05
1.20
1.20

12C

1.05
1.20
1.20

10B

12C
12C

10B
10B

(π+,Κ+)(π+,Κ+)(π−,Κ+)

16.0
18.0
0.007

11.1
0.43x10-3(π+,Κ+)(π+,Κ+)(π−,Κ+)

7.80
no data

10.0122

1.56x10-3
18Summary of 10ΛLi experiment• We have observed 10ΛLi bound state for the first time.
• No distinct peak → statistics and/or nuclear structure• Cross section– ~ 10-3 as compared to (π+,K+) reaction (having a goodsensitivity)– ~ twice larger @ 1.2 GeV/c than @1.05 GeV/c– about one order smaller than a theoretical estimate witha two-step meson charge-exchange process--> a Σ- production, Σ-p -> Λn process may contribute19

To J-PARC
At present at KEK,
no plan for extensions/new proposals concerning E438/E521→ J-PARC (LoI-08/09)
On-going experiments at KEK-PS (till shutdown)
E548 (T. Kishimoto et al.) @ K2
E549 (M. Iwasaki et al.) @ K5
E559 (K. Imai et al.) @ K6…
Other Activities (including potential activities)
at J-Lab., FINUDA, SPring8, RCNP, JAERI, …
R&D works for J-PARC experiments (spectrometers, detectors…)
LoI-06, 08, 09, 10, 21 (Strangeness Nuclear Physics)

J-PARC is strongly awaited.

20