Hypernuclear gamma-rayspectroscopyat J-PARC K1.8 Beam line
Tohoku Univ.
K.Shirotori
東北大学 大学院理学研究科
白鳥昂太郎
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Outline
Background of experiments
Requirement on setup
Setup, SKS & Hyperball-J
Detectors in detail, SKS & Veto counters
Summary
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Previous hypernuclear gamma-rayexperiments
Investigation of ΛN interaction by Λ hypernuclei.
(π+, K+) reaction @ KEK
Good spectrometer SKS(Momentum resolution ～1MeV/c)
Low background
Low production rate
(K-, π-) reaction @ BNL
High production rate
Spectrometer is worse than KEK
Large Background from Beam K-decay
Systematic studies of several hypernuclei → J-PARC
High production rate
+Background rejection
Good spectrometer
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Proposed “DAY-1” experiment E13
Several light hypernulcear gamma-rayspectroscopy experiments are planed.
(4ΛHe, 7ΛLi, 10ΛB, 11ΛB, 19ΛF)
(K-, π- γ) at pK = 1.5 GeV/c (500k/spill)
(Out going π-～1.4 GeV/c)
Magnetic spectrometers for (K-, π-) detection
Hyperball-J for Gamma-ray measurement
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HyperBall-J or HyperWall-J
Wall Type
Ball Type
Single Ge (r.e.70%) ～ 30
PWO background suppressionfor higher counting rate
Waveform readout
LN2 cooling
↓
Mechanical cooling by
Pulse tube
Target
Total photo peak efficiency
>5%
@ 1MeV (Geant4 simulation)
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Requirement on spectrometer forhypernuclear gamma-ray spectroscopy
To analyze 1.4GeV/c-scattered π- byexisting spectrometer system.
Large acceptance ～100[msr], θ～20[degree].
→Enough hypernuclear production yield.
Good momentum resolution 2～4[MeV/c].
→To distinguish excited states of hypernuclei.
Modify SKS (Superconducting Kaon Spectrometer )
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The K1.8 Beam line and SKS
Beam spectrometer
・BH1,2 : Time-of-flight
・BAC : π- veto (n=1.03)
SKS
・SAC : K- beam veto (n=1.03)
・SFV : K- beam veto
・STOF : Time-of-flight
Target : ～20 g/cm2
MWPC & DC
: Beam position measurement
Background Veto
・SMF : μ- from K-→μ-+ν
・SP0 : π- from K-→π-+π0
Hyperball-J : γray
Beam spectrometer
SKS
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Present SKS to New SKS
Momentum resolution
0.1%FWHM (0.72MeV/c)
@ 720 MeV/c, 2.2T
Maximum centralmomentum
1.0 GeV/c @ 2.7T
Acceptance
100 msr @0.72GeV/c
θ～20°
2.2T
Scattered particles are not focusedand present drift chambers(SDC3,4) are small for largereaction angle (half acceptance).
→Large acceptance bylarge drift chambers
Smaller bending angle(100°→60°)
→Momentum resolutiongets worse.
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Present SKS to New SKS
Momentum resolution
0.1%FWHM (0.72MeV/c)
@ 720 MeV/c, 2.2T
Maximum centralmomentum
1.0 GeV/c @ 2.7T
Acceptance
100 msr @0.72GeV/c
Parallel
scattering
2.7T
θ～20°
Scattered particles are not focusedand present drift chambers(SDC3,4) are small for largereaction angle (half acceptance).
→Large acceptance bylarge drift chambers
Smaller bending angle(100°→60°)
→Momentum resolutiongets worse.
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Present SKS to New SKS
2.7T
Scattered particles are not focusedand present drift chambers(SDC3,4) are small for largereaction angle (half acceptance).
→Large acceptance bylarge drift chambers
Smaller bending angle(100°→60°)
→Momentum resolutiongets worse.
θ～20°
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Present SKS to New SKS
SBS
K- beam directly hit SDC3,4.
↓
Scattering beam particles by heavymaterial (Pb, W)
300kHz→60kHz/wire @ 20mm cell
Scattered particles are not focusedand present drift chambers(SDC3,4) are small for largereaction angle (half acceptance).
→Large acceptance bylarge drift chambers
Smaller bending angle(100°→60°)
→Momentum resolutiongets worse.
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SKS : New configuration
SKS
・SAC : K- beam veto (n=1.03)
・SFV : K- beam veto
・STOF : Time-of-flight
DC : Beam position measurement
Background Veto
・SMF : μ- from K-→μ-+ν
・SP0 : π- from K-→π-+π0
Beam K
π
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SKS Acceptance & Momentum resolution
Acceptance ～120[msr] withlarge drift chambers (2[m]×1[m])
100[msr] for present SKS
Momentum resolution2.1[MeV/c] (bending angle ～60° w/multiple scattering)
0.8[MeV/c] for present SKS
Simulation program is checkedagainst previous SKSconfiguration
SKS performance is sufficient
for hypernucler gamma-rayspectroscopy
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Background rejection
K-→μ-ν (63.4%)
⇒Muon Filter
K-→π-π0 (21.1%)
⇒PiZero Veto
Beam K- decay products makeserious background
K-→π-π-π+ (5.58%)
K-→e-π0ν (4.87%)
K-→μ-π0ν (3.27%)
K-→π-π0π0 (1.73%)
Contribution is relatively small～150 trigger
Fake trigger ～1700/spill
True event trigger ～700/spill
Beam K
BAC
SAC
Target
20cm
μ
ν
Decay
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Muon Filter
Thick Material (ex. Iron)
μ-
π-
Scintillation
counter
Scintillation
counter
Only μ- can be detected.
Stopped by
hadronic interaction
Pass through
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Muon Filter
After
Before
89% of μ can be detected inthe trigger
In the offline analysis ～100%
Over kill for true π ～1.7%
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PiZero Veto
70% of π0 can be detected by2 set of 2[cm] lead plate andscintillation counter layer. (75%of γ from π0 hit the SP0)
Simulation in progress
Before
After
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Trigger rate
(K-,π-) Reaction rate ～700/spill
K-→μ-ν ～1320/spill
K-→π-π0 ～390/spill
K- Beam ～10/spill
3-body decay ～150/spill
～2570/spill
w/o Veto counters
True trigger ～350/spill
w/ Ge trigger and faketrigger greatlydecreased.
(K-,π-) Reaction rate ～700/spill
K-→μ-ν ～140/spill
K-→π-π0 ～120/spill
K- Beam ～10/spill
3-body decay ～150/spill
～1130/spill
w/ Veto counters
～500/spill
w/ Ge trigger
(K-, π- γ) at pK = 1.5 GeV/c (500k/spill)
Comparable to the presenttrigger rate
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Summary
Several hypernulcear gamma-ray experiments are planed at the J-PARCK1.8 beam line.
SKS is sufficient for hypernuclear gamma-ray spectroscopy.
Simulations in progress show a good vetocounter efficiency.
Estimation of background from heavycounter materials is necessary.
Backup
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Rough Kawazanyou (compared with BNLE930)
Beam 200k/spill→500k/spill : 2.5 times
Acceptance 60[msr]→120[msr] : 2 times
Hyperball 2.5%→6% : 2.4 times
S/N : 2 times
Cross section 1/3 times (0.9→1.5GeV/c)
→8 times
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Proposed “DAY-1” experiment E13
Spin-flip B(M1) measurement and gΛ in a nucleus
7ΛLi : Least ambiguities exist and most reliable
ΛN interaction study from p-shell hypernuclei
10ΛB and 11ΛB : Inconsistency exists. Not enough experimentaldata
Radial dependence of ΛN interaction from sd-shellhypernuclei
19ΛF : Simplest in sd-shell
Spin-flip property in hypernuclear production
4ΛHe : Easiest to observe a spin-flip state
(K-, π- γ) at pK = 1.5 GeV/c (500k/spill)
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Beam Momentum
n
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ΛN effective interaction
V(r) = V0(r) + V(r) sN・s+ VN(r) lN・sN
+ V(r) lN・s+ VT(r) S12
(Core nucleus：p-shell、Λ：s-shell)
→Radial Integrals 、SN、S、T are determinedby previous experiments
= 0.43 SN= -0.39 S= -0.01 T= 0.03[MeV]
Some inconsistencies appear !
Ex. 10ΛB puzzle → Theory fails to predictenergy spacing of ground state doublet
To solve these problems and for systematic studies of severalhypernuclei → J-PARC
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SKS Minus
Time-of-flight : STOF
Position measurement :SDC1～4
Beam veto : SAC
Beam veto : SFV
Veto counter, μ- from K-→μ-+ν : SMF
Veto counter, π- from K-→π-+π0 : SP0
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Time resolution
Flight time ～16[ns]
Path length ～4.6[m]
Momentum
Pk=1.5 GeV/c (ΔP/P=1.4x10-4)
Pπ form (K, π) reaction(ΔP/P=6.3x10-4)
Present TOF
→ 300[ps] w/o PHC
Present BH1,2
→ 200[ps] w/ PHC
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Beam Veto
SAC efficiency ～99%
→5k trigger /spill @ 500k/spill
SFV →～10 trigger
Reduction of acceptance7.5%
Beam size
σx=19.8[mm]
σy=3.2[mm]
(u=0.02, v=0.002)
SBS
SBS
K- beam directly hit SDC3,4.
↓
Scattering beam particles bysome material (Pb, W)
300kHz→60kHz @ 20mm cell
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3-body Decay
K-→π-π-π+ (5.58%)
K-→e-π0ν (4.87%)
K-→μ-π0ν (3.27%)
K-→π-π0π0 (1.73%)
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Muon Filter
89% of μ can be detected inthe trigger
In the offline analysis ～100%
Over kill for true π ～1.7%
After
Before
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Muon Filter
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Iron thickness
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PiZero Veto
70% of π0 can be detected by2 set of 2[cm] lead plate andscintillation counter layer. (75%of γ from π0 hit the SP0)
Simulation in progress
After
Before
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PiZero Veto
70% of π0 can be detected by2 set of 2[cm] lead plate andscintillation counter layer. (75%of γ from π0 hit the SP0)
Simulation in progress
After
Before
Beam K
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Percentage of decay in target 25cm
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Λ Hypernucleus
Λ hypernucleus → Λ is bound in a nucleus
The Baryon which isdifferent from nucleons(p/n)
N-N interaction → B-B interaction
Deeply bound
in a nucleus
w/o Pauli effect
The property of baryonchanging in the nuclearmedium
strangeness S= -1
M=1115.68 MeV
J=1/2+
I=0
Mean life=263.2 ps
Λ
Nucleus
Λ hypernucleus
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Λ Hypernucleus
The Baryon which isdifferent from nucleons(p/n)
N-N interaction → B-B interaction
Deeply bound
in a nucleus
w/o Pauli effect
The property of baryonchanging in the nuclearmedium
Systematic studies of several hypernuclei → J-PARC
Λ Hypernucleus
⇔ ΛN effective interaction
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Level scheme of 7ΛLi
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Calculated cross section for 7ΛLi
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B(M1) mesurement
