1

Hypernuclear physics is a good tool to match nuclear and particle

physics. The study of this field may help in understanding some

crucial questions:

four baryon weak interaction vertex;

YN and YY strong interactions;

change of hyperon and meson properties in the nuclear medium;

existence of di-baryon particles;

Origin of spin-orbit interaction

the role played by the quark degrees of freedom,

flavor symmetry and chiral models in nuclear and hypernuclear field.

HypernuclearHypernuclear && Strangeness nuclear physicsStrangeness nuclear physicsThe experimental approachThe experimental approach

2

HypernuclearHypernuclear Physics:Physics: the experimental approachthe experimental approach

1. Spectroscopy (different types of production hyperfine splittings)

2. Decays3. Γn/Γp puzzle4. The FINUDA experiment5. Σ hypernuclei studies6. Deeply bound kaonic nuclei7. Other topics of interest

3

The 3rd roundNew reactions with New Detectors1985 (π+,K+) started at AGS1990 S=-2 searches at AGS and KEK (Emulsion-counter hybrid technique)1993 S=-1 Λ Spectroscopy, Weak decay, SKS spectrometer1998 γ ray spectroscopy (Hyperball)

ΛΛΛΛN potential definition ΓΓΓΓn/ ΓΓΓΓp puzzle in the non-mesonic decays

The 3rd roundNew reactions with New Detectors1985 (π+,K+) started at AGS1990 S=-2 searches at AGS and KEK (Emulsion-counter hybrid technique)1993 S=-1 Λ Spectroscopy, Weak decay, SKS spectrometer1998 γ ray spectroscopy (Hyperball)

ΛΛΛΛN potential definition ΓΓΓΓn/ ΓΓΓΓp puzzle in the non-mesonic decays

The 2nd roundFirst Counter Experiments CERN & BNL1973 Stopped (K−,π−) at CERN1974 in-flight (K−,π−) at CERN PS and BNL AGS

very small spin-orbit splitting

The 2nd roundFirst Counter Experiments CERN & BNL1973 Stopped (K−,π−) at CERN1974 in-flight (K−,π−) at CERN PS and BNL AGS

very small spin-orbit splitting

The 1st round 1953 Discovery of Λ hypernucleiEmulsion detectors --- CERN PS, BNL AGS K− beam

ΛΛΛΛ potential depth about 1/2

The 1st round 1953 Discovery of Λ hypernucleiEmulsion detectors --- CERN PS, BNL AGS K− beam

ΛΛΛΛ potential depth about 1/2

50 years of 50 years of HypernuclearHypernuclear PhysicsPhysics

The Present (and future)

FINUDA@DAFNE(It)Jlab(USA)

2009J-PARC (Jp)

The Present (and future)

FINUDA@DAFNE(It)FINUDA@DAFNE(It)Jlab(USA)Jlab(USA)

2009JJ--PARC (Jp)PARC (Jp)

4

Production of Production of HypernucleiHypernuclei

A hyperon is produced by replacing a u or d quark with a strange one.

Strangeness exchange, i.e. strange beam (e.g.Kaons)

(K-,π-) and (K-stop,π-)

Associated production, i.e. energeticBeam (must produce ss pair)

K-(us): t~12ns cτ~3.7m secondary kaon beamlines (protons primary beam)Intense, energetic primary beams, create kaons by

ass. prod. on thick production targets. Usually degraders to stop K or thick tgts for decent

statistics poor mom. resolutionHyp. Production σ σ σ σ ~ 100mb; Typical I ~ 104s-1

Usually ππππ secondary, intense beamlinesHyp. Production σ σ σ σ ~ 1mb Typical I~107s-1

5

1. The (K -stopped,ππππ−−−− ) Reaction

and the in-flight (K -,ππππ−−−− )

The ( K-stopped,ππππ ) Reaction

1. Exchanges Strangeness 2. K-

stopped : captures from low l large n states3. In flight: mostly substitutional states (low statistics) 4. K-

stopped : surface Peaked5. K-

stopped :drawbacks related to stopping K’s(mom. Res.)

AK - ππππ−−−−

ΛΛΛΛA

Production of Λ-hypernucleiProduction of Λ-hypernuclei

Spectroscopy pion

6

2. The (π+,K + ) Reaction

Complementary to the ( K-,π- ) Reaction

Resolutions of ~2 MeV

Physically Large Targets

Production of Λ-hypernucleiProduction of Λ-hypernuclei

7

The Complementary Nature of the Mesonic Production Reactions

(π+,K + )

( K-,π- )

8

Production of Λ-hypernucleiProduction of Λ-hypernuclei

12C(e,e’K+)12ΛB12C(e,e’K+)12ΛB

++′+Λ→+ Kepe )()(γreal and virtual photoproductionσ ≈ 0.1 µb; Ibeam=1012 s-1

real and virtual photoproductionσ ≈ 0.1 µb; Ibeam=1012 s-1

Jlab-HSSN(E89-009)Jlab-HSSN(E89-009)

A novel technique, an experimental challenge• very low cross sections• more particles to be measured in the final state• very high beam intensities• very high beam quality ∆p/p≈10-5

• possible achievable resolution 350 keV FWHM• generates non-natural parity and charge symmetric

hypernuclei• difficult mesurement of hypernuclear decay

A novel technique, an experimental challenge• very low cross sections• more particles to be measured in the final state• very high beam intensities• very high beam quality ∆p/p≈10-5

• possible achievable resolution 350 keV FWHM• generates non-natural parity and charge symmetric

hypernuclei• difficult mesurement of hypernuclear decay

900 keV resolutiondemonstrated

900 keV resolutiondemonstrated

present best resolution with othertechniques: 1.5 - 2.0 MeV

present best resolution with othertechniques: 1.5 - 2.0 MeV

3. The (γ,K + ) Reaction

9

Hypernuclear Spectroscopy

Most of the info about the YN potential (and medium effects, etc…) comes from the knowledge of hypernuclei structure.

Momentum (energy) resolution is the crucial parameter in order to see (distinguish) different hypn. states.

Resolution strongly dependent on - Beam characteristics, - detection techniques- reaction type- …

10

π

π

2π

2π

π

2π

2π

π

π

p

∆p

mp

mmp

T

∆T ⋅+

++=

∆p/p≈0.6% FWHM ∆MH= ∆Tπ ~1.25 MeV FWHM∆p/p≈0.6% FWHM ∆MH= ∆Tπ ~1.25 MeV FWHM

Example: K-stopped +A H + ππππ−−−−

• BΛ=ΜΑ−1+ΜΛ−ΜΗ

• MH=ΜΑ+ΜΚ−Μπ –ΤΗ+ΤΑ+ΤΚ−Τπ

• BΛ=ΜΑ−1+ΜΛ−ΜΑ −ΜΚ+Μπ +Τπ

(ΤΗ ≅ ΤΑ ≅ ΤΚ=0)

Final spectroscopy quality will strongly depend on momentum (energy) resolution achieved forthe detected pion.

Pπ~270MeV/c

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Spectra from BNL Experiments

51ΛΛΛΛV

28ΛΛΛΛSi

12ΛΛΛΛC

40ΛΛΛΛCa

18ΛΛΛΛO

9ΛΛΛΛBe

3 MeV ResolutionHard to see States

(ππππ+,,,,K + ) expts.

12

The SKS HypernuclearSystem

Most of KEK’s results In the last 15 years obtained with the SKS spectrometer

ππππ+ / ππππ-

K+

D2 magnet

13

14

Experimental (ππππ+,,,,K + ) Produced Spectrum of 9ΛΛΛΛBe

17

OPEParreno et al.(1996)

OPE OME

Dubach et al. (1996)

OPE Ramos et al. (1997)

OPE OME

Ramos-Benhold et al. (1994)

Γ Γ Γ Γ Γ Γ Γ Γ nn / / Γ Γ Γ Γ Γ Γ Γ Γ ppModel

ΓΓΓΓn / ΓΓΓΓp

Noumi et al. (KEK 1995)

Szymanski et al. (BNL 1991)

Theory

Experiment

ΓΓΓΓn/ΓΓΓΓpexp >>>>>>>> ΓΓΓΓn/ΓΓΓΓp

th

ΓΓΓΓn/ΓΓΓΓp ratio puzzle!

Status of ΓΓΓΓn/ΓΓΓΓp of 12ΛΛΛΛC

0.190.190.270.270.200.200.830.83

0.120.12

0.100.10

1.331.331.331.33±±±±1.21/0.811.21/0.811.21/0.811.21/0.81

1.871.871.871.87±±±±0.590.590.590.59±±±±0.32/1.000.32/1.000.32/1.000.32/1.00

Experimental ProblemsExperimental Problems1) high threshold 1) high threshold 2) Large error bars2) Large error bars

Problems in determination Problems in determination method of method of ΓΓΓΓΓΓΓΓnn//ΓΓΓΓΓΓΓΓpp ratio ratio from datafrom data

1) model dependent1) model dependent2) Effects of FSI and 2N proces2) Effects of FSI and 2N processs

…but recently interesting news …

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ΛΛΛΛ

12ΛΛΛΛC g.s.

NMWDΛN →→→→ NN

N

N

Direct Measurement of the ΓΓΓΓn /ΓΓΓΓp ratio

Top Detector

Bottom Detector

Angular correlation( back-to-back, cosθθθθ<----0.8 0.8 0.8 0.8 )Energy correlation( energy sum ~ Q value~150MeV )

Angular correlationAngular correlation( back-to-back, cosθθθθ<----0.8 0.8 0.8 0.8 )Energy correlationEnergy correlation

( energy sum ~ Q value~150MeV )

Select ΛΛΛΛN→→→→NN events without FSI and from 2N process only

Ynp=Nnpx ΩΩΩΩnpx εεεεnx εεεεpx (1-RFSI)npYnn=Nnnx ΩΩΩΩnnx εεεεnx εεεεnx (1-RFSI)nn

By charge symmetry (1-RFSI)np=(1-RFSI)nn

~ =

YYnpnp==NNnpnpxx ΩΩΩΩΩΩΩΩnpnpxx εεεεεεεεnnxx εεεεεεεεppxx (1(1--RRFSIFSI))npnp

YYnnnn==NNnnnnxx ΩΩΩΩΩΩΩΩnnnnxx εεεεεεεεnnxx εεεεεεεεnnxx (1(1--RRFSIFSI))nnnnBy charge symmetry (1-RFSI)np=(1-RFSI)nn

~ =

nnnnp

pnpnn

εΩYεΩY

××××

p

n

Γ

Γ

np

nn

NN

NucleonNucleon

19

p

n

ππππ+

K+

NT: 20cm××××100cm××××5cmT3: 10cm××××100cm××××2cmT2: 4cm××××16cm××××0.6cm

NT: 20cm××××100cm××××5cmT3: 10cm××××100cm××××2cmT2: 4cm××××16cm××××0.6cm

Solid angleNeutral: 26.5%Charged : 10%

Decay armDecay arm

Active Target

SETUPSETUP

beambeam

Charged particle：：：：・・・・TOF (T2→→→→T3)・・・・tracking（（（（PDC））））

Neutral particle：：：：・・・・TOF (target→→→→NT)・・・・T3 VETO

(KEK-PS K6 & SKS)

NTNT

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•The np- and nn-pairs from NMWD of 12ΛΛΛΛC were observed

successfully.

The energy sum of back-to-back np- and nn- pairs are approximately equal to the Q-values(~150MeV) of the NMWD.

ΛN nN process were clearly identified !!

•We got Γn/Γp ratio of 12ΛΛΛΛC at cos <-0.8 and EN>30MeV .

ΓΓΓΓn/ΓΓΓΓp ~ Nnn/Nnp ~ 0.40 ±±±±0.09 (statis. ) (Preliminary!! )

(expected systematic error ~ ±0.04)

Consistent with recent theoretical calculations !!!!

Summary (of a recent talk by J.Kim)

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・・・・2-body ΛΛΛΛN effective interaction

ＬＬＬＬTowards hyper-fine splitting understanding: measuring γγγγ-rays

24

Towards hyper-fine splitting understanding: measuring γγγγ-rays

Hyperball project- High-resolution γ-ray spectroscopy using Ge detectors

• Motivation- study of ΛN spin-dependent interaction via hypernuclear

structure high-resolution is required γ-ray spectroscopy using Ge detectors

• Hyperball- 14 Ge detecotors of 60% relative efficiency- BGO ACS- solid angle: 15% of 4π- photo-peak efficiency ~3% at 1 MeV

Results from recent experiments

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Experiments using hyperball

• KEK-PS E419 (1998)- spin-spin force in - glue-like role

• BNL-AGS E930 (1998)- spin-orbit force in

• BNL-AGS E930 (2001)- tensor force in- in analysis

• KEK-PS E509 (2002)- stopped K- in analysis

• KEK-PS E518 (2002)-

Li7Λ

Be9Λ

ΛO16

ΛB11

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KEK-PS E419(1) -- overview

• The first experiment at KEK (Tsukuba, Japan)• studied hypernucleus using 7Li(π+,K+γ) reactionLi7

Λ

7/2+

5/2+

3/2+

1/2+

7Λ LiΛ Li

M1

E2

1+

3+

6Li0

(MeV)

2.19

π+

K+

E2

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KEK-PS E419(2) -- Results

• Two peaks observed• These attributed toM1(3/2+ 1/2+) andE2(5/2+ 1/2+)transitions in

• Eγ = 691.7±0.6±1.0 keV2050.1±0.4±0.7 keV

• Peak shape analysis(Doppler shift attenuationmethod)

B(E2)=3.6±0.7 e2fm4

• For details, seeH. Tamura et al., PRL84(2000)5963K. Tanida et al., PRL86(2001)1982

Li7Λ

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KEK-PS E419(3) -- discussion

• Eγ(M1) = 692 keV gives strength of ΛN spin-spin force- 6Li(1+) state has pure 3S1 (α+d) structure ∆ = 0.48 ~ 0.50 MeV

(D. J. Millener, NPA691(2001)93c,H. Tamura et al., PRL84(2000)5963)

• B(E2) is related to hypernuclear size or cluster distance between αααα and d as B(E2) ∴ <r2>2

(T. Motoba et al., PTP70(1983)189)• Without shrinkage effect, B(E2) is expected to be

8.6±0.7 e2fm4 from B(E2) data of 6Li.• Present result (3.6±0.7 e2fm4) is significantly smaller strong evidence for gluestrong evidence for glue--like rolelike role

• (3.6/8.6)1/4 = 0.81±0.04 shrinkage of 19±±±±4%(K. Tanida et al., PRL86(2001)1982)

29

BNL-AGS E930(1)

• Experiment performed at BNL (New York, USA) • Measured γ ray from created by 9Be(K−,π−) reactionBe9

Λ

3/2+

5/2+

1/2+

9Λ BeΛ

E2

0+

2+

8Be0

(MeV)

3.04 L=2• ∆E(5/2+,3/2+) ΛN spin-orbit force, SΛ(core structure: 2α rotatingwith L=2)

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BNL-AGS E930(2)

• Two peaks separated!• |∆E| = 31±3 keV - very small indeed surprisingly small spinsurprisingly small spin--orbit forceorbit force (~ 1/100 of NN case)

(H. Akikawa et al., PRL88(2002)082501)

5/2+,3/2+ 1/2+

Eγ(keV)2000 2500 3000 3500

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END OF

lesson 3