Study on Λ-Hypernuclei with the Charge-Exchange Reactions · 2006. 6. 30. · Reaction mechanism...
Transcript of Study on Λ-Hypernuclei with the Charge-Exchange Reactions · 2006. 6. 30. · Reaction mechanism...
Study on Λ-Hypernuclei with the Charge-Exchange Reactions
Atsushi Sakaguchi (Osaka Univ.)
Collaboration:Osaka U., KEK, Osaka E. U., RIKEN, Seoul Natl. U., JAEA, U. Torino, INFN
and INAF-IFSI
Proposal for J-PARC 50GeV PS
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AbstractStudies on Λ-hypernuclei
with Charge-Exchange (CX) reactions
Proposal of experiments (at Day-1)Exp.1: Production of neutron-rich hypernuclei
Production of exotic hypernuclei⇒ Λ−N interaction in neutron-rich environment⇒ EoS and structure of neutron stars
Exp.2: Non-mesonic weak decay(NMWD) of 4ΛHeSpin-isospin structure of Λ-Nucleon weak int.⇒ “ΔI=1/2 rule” in NMWD of hypernuclei
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Atomic NucleiStable carriers of baryon numbers
Attractive NN int.⇒ Guarantees formation of “Matter”
Repulsive NN int.⇒ Avoids collapse to black hole
Interplay of NN interactions⇒ Drives evolution of stars and the universe
Knowledge on NN interactionNuclear structureNN scattering data
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Hypernuclei
S
“Stable” carriersof baryon numbers
“Stable” against strong int.Quasi-stable objects
Stable in neutron starsYN and YY interaction
Structure of neutron stars
Source of info. on YN and YY interaction
Structure of hypernucleiProduction of hypernucleiLevel energy measurement
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Structure study on hypernucleiSurvey only limited region of isotopesLack of spectroscopic tools
+K+π
C12ΛC12Ordinary
production reaction
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Charge-Exchange ReactionsNew category of production reaction
New hypernuclear speciesMirror and neutron-rich hypernuclei
+K−π
Be12ΛC12Charge-Exchange
reaction
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Exotic ObjectsHeaviest stable hydrogen ?
TritonHeaviest stable hydrogen
Only with nucleonsSuper-heavy hydrogen1.7 MeV unbound
Addition of Λ hyperonHyper-heavy hydrogen~ 4 MeV boundHeaviest stable hydrogenDouble of 3H
H5
H6Λ
H3
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Our StrategyDevelop charge-exchange reactions
Single charge-exchange (SCX) reactions
Suitable to produce mirror-hypernuclei
Double charge-exchange (DCX) reactions
Production of neutron-rich hypernuclei
( )0,K−π
He4
H
He
4
4
Λ
Λ
c
NCX
SCX
( ) ( )+−+− ππ ,, KK
Systematic study of hypernuclei
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Practical problemsSmall detection efficiency for SCX: 10-1~10-2
Small reaction cross section for DCX: 10-3
High-intensity beam line for CX reactionPion beam intensity ~ 109/spill: 102
Override small yieldHigh-resolution achievable at the same time
A long-range planConstruction of new beam line and spectrometer
Experiments at Day-1Start study with available infrastructure
( )0, K−π
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Experiments at Day-1 (1/2)Production of n-rich hypernuclei with DCX
Structure of neutron-rich hypernucleiWhat we can learn ?ΛN strong interaction in N≫Z environmentClose connection to EoS in neutron stars
Non-mesonic weak decay of 4ΛHeMeasurement of Λn→nn weak processComplementary with Λp→pn in 4ΛHWhat we can learn ?Spin-isospin structure of ΛN weak interactionTest of “ΔI=1/2 rule”
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Neutron-Rich HypernucleiKEK-PS-E521
First successful experimentn-rich hypernucleiDCX reaction
Reaction studied
Cross section~10 nb/sr
small cross section~10-3 of ordinary reaction
ExperimentalNo problem except for the small cross sectionWe need good beam line and good spectrometer
( ) LiKB 1010 , Λ+−π
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Experimental setup
K1.8 Beam lineπ beam intensity ~107 / spill
SKS Spectrometermoved from KEK-PSsolid angle ~ 100 msr
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Proposed experimentReaction mechanism of DCX reactionProduction of typical n-rich hypernuclei
Another optionStudy on structure of n-rich hypernucleiProduction of exotic hypernuclei
( ) ( ) Be,CLi,B 12121010Λ
+−Λ
+− KK ππ
HHeLi 6910ΛΛΛ
Similar reactionand structure
Cross section and structure may differ
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Expected yieldProduction of 9ΛHe
Assume similar cross section as 10ΛLi
Requested beamtime for this study2 weeks for 9ΛHe and 2 weeks for 6ΛH (4 weeks in total)+ Beam tuning and energy/efficiency calibration
Parameters Values
π− beam momentumπ− beam intensity
PS acceleration cycle9Be target thickness
Reaction cross sectionSpectrometer solid angleSpectrometer efficiency
1.2 GeV/c107 /spill3.4 sec
3.5 g/cm2
10 nb/sr0.1 sr0.5
NBeam
TCycle
NTarget
dσ/dΩΩSP
εSP
CycleSPSPA
TargetBeam T
TimeddN
NNYield ××Ω×
Ω×××= εσ
9~400 events/2weeks
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Experiments at Day-1 (2/2)Production of n-rich hypernuclei with DCX
Structure of n-rich hypernucleiWhat we can learn ?ΛN strong interaction in N≫Z environmentClose connection to EoS in neutron stars
Non-mesonic weak decay of 4ΛHeMeasurement of Λn→nn weak processComplementary with Λp→pn in 4ΛHWhat we can learn ?Spin-isospin structure of ΛN weak interactionTest of “ΔI=1/2 rule”
Need SCX
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Non-Mesonic Weak DecaySpin-isospin structure of NMWD
Branching ratio tellDecay asymmetry tellPossible answer: 1S0 amplitude (a and/or b)Observable sensitive to 1S0
othersfd >>≈fdorfd <<>>
( )( )npp
nnn→ΛΓ→ΛΓ
( )pθασ cos10 +
( ) ( )H;He; 44ΛΛ →ΛΓ→ΛΓ nppnnn
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Beam line and spectrometerK1.8 beam line: 1.1GeV/c π+ beam ~107/spillSKS spectrometer: ~100 msr
Expected yield of 4ΛHe(0+)
Yield ~ 38k 4ΛHe(0+)/day
Parameters Values
π+ beam momentumπ+ beam intensity
PS acceleration cycleLiquid 4He target thickness
Reaction cross sectionSpectrometer solid angleSpectrometer efficiency
1.1 GeV/c107 /spill3.4 sec2 g/cm2
10 μb/sr0.1 sr0.5
NBeam
TCycle
NTarget
ds/dΩΩSP
εSP
CycleSPSPA
TargetBeam T
TimeddN
NNYield ××Ω×
Ω×××= εσ
4
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Decay particle detector
proton
neutron
−π
Direct measurementDetect nn and np pairs
Estimated yieldsΛn→nn: ~120 events/2weeksΛp→np: ~3200 events/2weeks
( )( )pYieldnYield ( )
( )npYieldnnYield
Veto for negative pion BGRejection with CDCMC study tells S/N≫10
Back-to-back kinematicsSelection of ΛN→NN processRemove ΛNN→NNN process
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SummaryWe propose studies on Λ-hypernuclei
with Charge-Exchange (CX) reactionsProposal of experiments (at Day-1)Exp.1: Production of neutron-rich hypernuclei
Exp.2: Detailed study on NMWD of 4ΛHe
Outputs expectedΛN strong int. in neutron-rich environmentSpin-isospin structure of ΛN weak interaction
HHe 69ΛΛ
( )Henn;n 4Λ→ΛΓ pin down 1S0 contribution
Production of exotic hypernuclei