PS review
June 7, 2004

γ-Ray Spectroscopy of Λ Hypernuclei
E419, E509, E518
Dept. of Physics, Tohoku University
H. TamuraContents
1. Motivation and Hyperball
2. E419 (7ΛLi) and after
3. E518 (11ΛB)
4. E509 (hyperfragments)
5. Future

History ofPrecision γ Spectroscopy of Λ Hypernuclei’96-’98

Construction of Hyperball’98 Apr-May

KEK-E419 (K6/SKS) : 7ΛLi

’98 Dec

BNL-E930 (D6) : 9ΛBe

’01 Sep-Nov BNL-E930 (D6) : 16ΛO / 15ΛN, 10ΛB, etc.
’02 Apr

KEK-E509 (K5) : hyperfragments (7ΛLi)’02 Sep-Oct

KEK-E518 (K6) : 11ΛB

Future: before J-PARC(KEK, to be proposed) 12ΛC/ 11ΛB, 4ΛHe
(BNL E930, E964)
Future: at J-PARC

Hyperball collaboration at KEK
E419, E509, E518 (1998, 2001,2002)
Tohoku Univ.

H. Tamura, D. Abe, K. Araki, T. Endo, Y. Fujii, O. Hashimoto, M. Kameoka, A. Matsumura,Y. Miura, T. Miyoshi, K. Mizunuma, S.N. Nakamura, H. Nomura, Y. Okayasu, K. Ozawa,T. Saito, J. Sasao, S. Satoh, T. Takahashi, M. Ukai, H. Yamauchi

Kyoto Univ.

H. Akikawa, Y.Fukao, K. Imai, K. Miwa, T. Murakami, M. Niiyama, S.Ota,
H. Takahashi, S.Terashima, M. Togawa

KEKK. Aoki, Y. Kakiguchi, T. Maruta, T. Nagae, H. Noumi, H. Outa, Y. Sato, M. Sekimoto, A. Toyoda

Osaka EC Univ.

T. Fukuda, H. Hotchi, W. Imoto, P.K. Saha

CIAE

H.H. Xia, S.H. Zhou, L.H. Zhu

Seoul Nat’l Univ.

H.C. Bhang, J.H. Kim

RIKEN

K. Tanida

Osaka Univ.

S. Ajimura

BNLH. Hotchi

Hampton Univ.

L.TangNorth Carolina U. R.I. Sawafta
Sejong Univ.

Y.D. Kim

GSI

T. Saitoh

ITEPA. Krutenkova

Hyperball

Large acceptance for small
hypernuclear γ yields
Ge (r.e. 60%) x 14
Ω ~ 15%εpeak~ 3% at 1 MeV

 High-rate electronics

for huge background
1 TeV/sec, 100 kHz
 BGO counters for π0 andCompton suppression

Resolution of hypernuclear
spectroscopy
1 MeV -> 2 keV FWHM

(Tohoku/ Kyoto/ KEK, 1998)

Motivations ofhypernuclear γ spectroscopy Baryon-baryon interactions E419, E518
Λ hypernuclear structure

ΛN int. (meson or quark models)c.f. nuclear structure

NN int. (phenomenologically known)

Unified understanding of B-B interactions

 Impurity effects

E419

Change of size and shape (shrinkage),
New symmetries, Change of collective motions,...

 Medium effects probed by hyperons free from Pauli
Λ-spin-flip B(M1) → gΛE518

γ spectroscopy andΛN spin-dependent interactions
・Low-lying levels of Λ hypernucleus

・2-body ΛN effective interaction

Dalitz and Gal, Ann. Phys. 116 (1978) 167
C31 (1985) 499
Millener et al., Phys. Rev.テンソル力Ｔ

E419: γ-spectroscopy of 7ΛLi
First exp. with HyperballRun in April-May, 1998, at K6, 80 shifts

B(E2) -> shrinking effectSpin-flip M1 -> ΛN spin-spin force

Setup for E419 (E518)

SKS only (E336)

γ spectrum of 7ΛLi
KEK E419 : SKS + Hyperball
Excitation Energy

Tamura et al., PRL 94(2000) 5963

First observation of well-identified hypernuclear γ rays with Ge.

Results
on 7ΛLi

Predicted by Motoba et al.,Prog.Theor.Phys.
70 (1983) 189.

shrinking effectspin-spin interaction∆ = 0.50 MeV
N- LS interaction
SN~ -0.4 MeV

β<r2>
RB(E2) ∝|<f| e r2 Y2 |i>|2∝R4 or (β<r2>)2
Tanida et al., PRL 86(2001) 1982

Publicityof E419
andHyperball
Butsuri,June 2001

Asahi,
8 July 2000

PRL 84(2000) 5963
PRL 86(2001) 1982
PLB 579 (2004) 258
and more to come..

News of the week
Science 291, 9 March 2001

Results on ΛN interaction by E419+E930“Hypernuclear Fine Structure”∆E = 2.47SΛ+ 0.94T

E419

3/2+2+3/2-1-

1/2-1-43 keV

7/2+3+E930

5/2+5/2+-310 keV∆E = 0.68SN
3/2+1+692 keV

0+1/2+6Li∆E = 1.44 ∆ - 0.27T
7 Li
Λ

∆ = 0.4 MeVSΝ = - 0.4 MeV

1/2+8Be

15O9 BeΛSΛ = - 0.01 MeV

0-26 keV∆E = - 0.39 ∆ + 1.38SΛ+ 7.82T
16 O
ΛT = 0.03 MeV

All the spin-dependent force parameters
determined.

E518: γ-Spectroscopy of 11ΛB
Run in Oct. 2002 at K6, 80 shifts

many bound levels

M1

1+3/2+1/2+E2
7/2+3+5/2+10B

11 B
ΛExpected levels

Purposes: τ(3/2+) 〜 0.5 ps (Millener)
Stopping time 〜 1.0 ps by (π+,K+)-> B(M1) : measurable
by Doppler shift attenuation method
 Level energies-> Cross check ofΛN spin-dependent interactions

B(M1) and µΛ in nucleusµΛ in nucleus -> Possible modification of baryons in nuclear matter
Effect of meson-exchange current (small)
Direct measurement of µΛ very difficultbut
Spin-flip B(M1) -> gΛ

11 B
Λ

MassSpectrum

Thin (1cm) target

Calc. by MotobaAboundregion

10cm target : 0.85×1012π+
6cm target : 0.75×1012π+(Proposal : 10cm, 2.1x1012π+)=>
Beam x Target thick. x Ge eff.
＝ 50% of proposal

Thick (6cm, 10cm)
targetB
unboundregion

γ-Ray Spectrumof 11ΛBAB

Six 11ΛB γ-rays observed.
Eγ(keV)

Numberof Events

Relative
Intensity

Lifetime Fit

Preliminary
stat.error only

Fit both spectra (w/o and w/ Doppler correction)with simulated peak shapes for various lifetimes=> 0.15+0.03-0.02 ps=> > 5.24 ps

Eγ (keV)263.4±0.05
456.6±0.02
503.7±0.02
567.0±0.02
1481.9±0.02
2474.7±0.02lifetime (ps)0.39+0.16-0.11
0.21+0.08-0.05
0.34+0.09-0.06
0.15+0.03-0.02> 5.240.04+0.03-0.02=> 0.04 +0.03-0.02 ps

Assignment of
11 B (1482 keV) lineΛE2 (1/2+1→5/2+1) because Long lifetime-- too long for M1( >5 ps => B(M1) < 10-3 [µN2] ) Largest yield -- 1/2+1 collects yields
from upper levels
 Gated mass spectrum – showing
contribution from upper levels also
11 B mass spectrum
Λfor 1482 keV γ-ray events

γ-rays expected to be observed (Millener)

E518 Present Status Six transitions in 11ΛB were observed.
 E2 energy (1482 keV) significantly larger thanthe prediction (1020 keV) from already-determinedparameters-> SN inconsistent with the other data (7ΛLi, 12ΛC, 13ΛC, 16ΛO)-> core (10B) w.f. incorrect? –- feedback to structureof normal nuclei?
PLB to be published.

 Assignment of all the other observed γ-rays seems
difficult-- γγ coincidence necessary with a higher efficiency
detector

E509: Hypernuclear Spectroscopyof hyperfragments with stopped KApril 2002, 40 shifts, K.Tanida
Direct reactions : (π+, K+ γ), (K-, π- γ)
 Hypernuclei can be idenitified well.
 But, low yields –~one month pertarget

Indirect reaction: (stopped K-, γ)

KEK K5-- in-beam method 650 MeV/c Large production yield ofK“hyperfragments” from stopped Kabsorption ( ~10% per stopped K- )
 Various hypernuclear species
including n/p-rich ones
 But, more background and difficult 7Li, 9Be, 10B,
11B, 12C targets
identification--> Test feasibility

(stopped K-, γ) spectrumCandidates of hypernuclear γ rays
 Not normal nuclear γ rays
 Target dependence Prompt timing (< 5ns)Eγ (keV)target1302

9Be,10B,11B

2049

10B,11B,12C

10B target

E509 results (1):2049 keV line(stopped K-, γ)2050.1±0.4±0.7 keV(E419)

 7ΛLi : E2(5/2+→1/2+)
observed with a large yield,
516±74 counts in 3.5 days
c.f. E419 7Li (π+,K+γ) 7ΛLi
188±17 counts in 25 days=> Abundant γ-ray yield Production rate of 7ΛLi (5/2+) :0.075±0.016% per stopped K- on 10B
PLB to be published.

 7ΛLi : M1(7/2+→5/2+) not observed(small statistics for γγ coincidence)

2050 keV
7 Li (5/2+->1/2+)
ΛE509 results (2):1303 keV line
Unknown candidate of
hypernuclear γ ray at
1302.0±0.6 keV-> 8ΛLi, 9ΛLi, .. ?

E509 summary(stopped K-,γ) is found useful, but
γγ coincidence necessary
combination with direct reactions

Before J-PARC
Future Plans

Construction of Hyperball2 – finishing soon.
KEK: 12ΛC /11ΛB, 4ΛHe at K6 (2005), to be proposed.
-- ΛN force cross-check by 12ΛC : solve inconsistency problem of 10ΛB
necessary for J-PARC strategy-- B(M1) of 11ΛB possible-- 4ΛHe for Charge Symmetry Breaking

BNL: E930-3 (more p-shell), E964 Ξ-atomic X-rays--approved but difficult to get beam time.
Preparation for J-PARC (R&D for a “faster” system)

Training of students at Jlab (Hall-C) and DAFNE(FINIDA)

J-PARC: γ spectroscopy is a “Day-1” experiment.


Systematic study of all light (A<30) hypernuclei
Medium heavy hypernuclei
Mirror and n-rich hypernuclei using (K-,π0) and hyperfragments (CSB, shrinkangeof n-halo,..)Systematic measurement of B(M1) for magnetic moment of Λ in a nucleus

Hyperball2 under construction, ready by fall, 2004


Clover Ge (r.e. >120%)+BGO

x 6 added

Photo-peak efficiency~ 2.5% -> 5% at 1 MeVγγ efficiency -> x 4

VME-based fast readout



Test Exp at Tohoku
Cyclotron

To be used at KEKand BNL in 2005-

Summary and Remarks
Precision γ spectroscopy of Hypernuclei achieved
103 improvement of resolution-> ΛN interaction, shrinking effect, gΛ in nucleus
A breakthrough in strangeness nuclear physics
Why was it born at KEK-PS so successfully?
 Well established SKS system andPerfect support by SKS group Frequent beam time (’95-’98) for Hyperball R&D andtraining students-> Please minimize no-beam period before J-PARC.
-> Construction of “Standard System” =SKS at J-PARC
is indispensable.

12 C / 11 BΛΛand 4ΛHe with K6/SKS

Cross check of ΛN forces
B(M1) possible
Help E518 data assignment

Cross check of ΛN forces[similar structure to10 B(contradictory to theΛother data)]

4 He – Charge Symmetry
Λ

Breaking
Observed CSB looks
spin-independent.
ΛN-ΣN coupling gives
spin-dependent CSB.

stop K- on 6Li by NaI (1979)

Only one data
Bad quality

Liq. 4He 10cm (1.25 g/cm2)
0.4x1012 π+ (20 shifts)
SKS 0 deg

Hyperball+SKS

4 H* : (e,e’K+) at Jlab/HKS
Λ(K-,π0γ) at J-PARC

Present status of γ spectroscopy

PLB 579 (2004) 258-> “Table of hyper-isotopes”

7 LiΛ

Best-studied Hypernucleus

KEK E419
7Li (π+,K+γ) 7 LiΛNon-spin-flip in weak decay Λ ->N π
7 Li (1/2+) -> 7 Be*(1/2-) + πΛΛ
7 Li (3/2+) -> 7 Be*(3/2-) + πΛΛ

g.s.spin = 1/2

Sasao et al., PLB 579 (2004) 258

Plans of γ spectroscopy
at J-PARC (+ Hyperball-J)(1) Complete study of light (A<30) hypernuclei(2) Systematic study of medium and heavy hypernuclei(K-,π- γ) spin-flip/ no-flip productions

ΛN force (ΛN−ΣN, p-wave,..)B(E2)-> shrinkage, New symmetries(3) n-rich/ p-rich/ mirror hypernuclei(K- , γ γ) in-beam method(K-, π0 γ) mirror hypernuclei

Charge sym. break in ΛN force
Shrinkage of n-halo(4) Spin-flip B(M1)(K-,π- γ), (π+,K+ γ) Doppler shift atten.
(K-,π- γ p) γ-weak coincidenceµΛ in nuclei (ρ-dependence)(5) Double strangenss (Ξ− atom X rays and ΛΛ-hypernuclei)(K-, K+ γ)

ΞN, ΛΛ interactions