Hypernuclear gammaray spectroscopy at JPARC K1'8 Beam line

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Hypernuclear gamma-ray spectroscopy at J-PARC
K1.8 Beam line

• Tohoku Univ.
• K.Shirotori
• ???? ????????
• ?????

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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-ray experiments

• Investigation of ?N interaction by ? hypernuclei.

• (p, K) reaction _at_ KEK
• Good spectrometer SKS (Momentum resolution
  1MeV/c)
• Low background
• Low production rate

• (K-, p-) reaction _at_ BNL
• High production rate
• Spectrometer is worse than KEK
• Large Background from Beam K- decay

High production rate Background rejection
Good spectrometer
Systematic studies of several hypernuclei ? J-PARC
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Proposed DAY-1 experiment E13

• Several light hypernulcear gamma-ray spectroscopy
  experiments are planed.
• (4?He, 7?Li, 10?B, 11?B, 19?F)
• (K-, p- ?) at pK 1.5 GeV/c (500k/spill)
• 
  (Out going p-1.4 GeV/c)
• Magnetic spectrometers for (K-, p-) 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 suppression for higher counting
  rate
• Waveform readout

LN2 cooling ? Mechanical cooling by Pulse tube
Target
Total photo peak efficiency gt5 _at_ 1MeV (Geant4
simulation)
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Requirement on spectrometer forhypernuclear
gamma-ray spectroscopy

• To analyze 1.4GeV/c-scattered p- by existing
  spectrometer system.
• Large acceptance 100msr, ?20degree.
• ?Enough hypernuclear production yield.
• Good momentum resolution 24MeV/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 p- veto (n1.03)
SKS
SKS
SAC K- beam veto (n1.03) SFV K- beam
veto STOF Time-of-flight
MWPC DC Beam position measurement
Background Veto
Target 20 g/cm2
SMF µ- from K-?µ-? SP0 p- from K-?p-p0
Beam spectrometer
Hyperball-J ?ray
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Present SKS to New SKS

• Scattered particles are not focused and present
  drift chambers (SDC3,4) are small for large
  reaction angle (half acceptance).
• ?Large acceptance by large drift chambers
• Smaller bending angle(100?60)
• ?Momentum resolution gets worse.

2.2T
?20
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Present SKS to New SKS

• Scattered particles are not focused and present
  drift chambers (SDC3,4) are small for large
  reaction angle (half acceptance).
• ?Large acceptance by large drift chambers
• Smaller bending angle(100?60)
• ?Momentum resolution gets worse.

2.7T
?20
Parallel scattering
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Present SKS to New SKS

• Scattered particles are not focused and present
  drift chambers (SDC3,4) are small for large
  reaction angle (half acceptance).
• ?Large acceptance by large drift chambers
• Smaller bending angle(100?60)
• ?Momentum resolution gets worse.

2.7T
?20
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Present SKS to New SKS

• Scattered particles are not focused and present
  drift chambers (SDC3,4) are small for large
  reaction angle (half acceptance).
• ?Large acceptance by large drift chambers
• Smaller bending angle(100?60)
• ?Momentum resolution gets worse.

SBS
K- beam directly hit SDC3,4. ? Scattering beam
particles by heavy material (Pb,
W) 300kHz?60kHz/wire _at_ 20mm cell
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SKS New configuration
SKS
SAC K- beam veto (n1.03) SFV K- beam
veto STOF Time-of-flight
DC Beam position measurement
Background Veto
SMF µ- from K-?µ-? SP0 p- from K-?p-p0
p
Beam K
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SKS Acceptance Momentum resolution

• Acceptance 120msr with large drift chambers
  (2m1m)
• 100msr for present SKS
• Momentum resolution 2.1MeV/c (bending angle
  60 w/ multiple scattering)
• 0.8MeV/c for present SKS

Simulation program is checked against previous
SKS configuration
SKS performance is sufficient for hypernucler
gamma-ray spectroscopy
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Background rejection
Target 20cm
BAC
SAC
µ
Beam K
?
Decay
Beam K- decay products make serious background

• K-?µ-? (63.4)
• ?Muon Filter
• K-?p-p0 (21.1)
• ?PiZero Veto

Fake trigger 1700/spill True event trigger
700/spill
K-?p-p-p (5.58) K-?e-p0? (4.87) K-?µ-p0?
(3.27) K-?p-p0p0 (1.73)
Contribution is relatively small 150 trigger
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Muon Filter
Thick Material (ex. Iron)
µ-
Pass through
p-
Stopped by hadronic interaction
Scintillation counter
Scintillation counter
Only µ- can be detected.
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Muon Filter
Before
After

• 89 of µ can be detected in the trigger
• In the offline analysis 100
• Over kill for true p 1.7

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PiZero Veto
Before
After

• 70 of p0 can be detected by 2 set of 2cm lead
  plate and scintillation counter layer. (75 of ?
  from p0 hit the SP0)

Simulation in progress
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Trigger rate
(K-, p- ?) at pK 1.5 GeV/c (500k/spill)

• (K-,p-) Reaction rate 700/spill
• K-?µ-? 1320/spill
• K-?p-p0 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 fake
trigger greatly decreased.
1130/spill w/ Veto counters

• (K-,p-) Reaction rate 700/spill
• K-?µ-? 140/spill
• K-?p-p0 120/spill
• K- Beam 10/spill
• 3-body decay 150/spill

500/spill w/ Ge trigger
Comparable to the present trigger rate
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Summary

• Several hypernulcear gamma-ray experiments are
  planed at the J-PARC K1.8 beam line.
• SKS is sufficient for hypernuclear gamma-ray
  spectroscopy.
• Simulations in progress show a good veto counter
  efficiency.
• Estimation of background from heavy counter
  materials is necessary.

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Backup
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Rough Kawazanyou (compared with BNL E930)

• Beam 200k/spill?500k/spill 2.5 times
• Acceptance 60msr?120msr 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
(K-, p- ?) at pK 1.5 GeV/c (500k/spill)

• Spin-flip B(M1) measurement and g? in a nucleus
• 7?Li Least ambiguities exist
  and most reliable
• ?N interaction study from p-shell hypernuclei
• 10?B and 11?B Inconsistency
  exists. Not enough experimental data
• Radial dependence of ?N interaction from sd-shell
  hypernuclei
• 19?F Simplest in sd-shell
• Spin-flip property in hypernuclear production
• 4?He Easiest to observe a
  spin-flip state

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Beam Momentum
K- n -gt L p-
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?N effective interaction
V(r) V0(r) Vs(r) sNsL VN(r) lNLsN

VL(r) lNLsL VT(r) S12
(Core nucleusp-shell??s-shell)
? Radial Integrals D?SN?SL?T are determined by
previous experiments
D 0.43 SN -0.39 SL -0.01 T 0.03 MeV

• Some inconsistencies appear !
• Ex. 10?B puzzle ? Theory fails to predict energy
  spacing of ground state doublet

To solve these problems and for systematic
studies of several hypernuclei ? J-PARC
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SKS Minus

• Time-of-flight STOF
• Position measurement SDC14
• Beam veto SAC
• Beam veto SFV
• Veto counter, µ- from K-?µ-? SMF
• Veto counter, p- from K-?p-p0 SP0

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Time resolution

• Flight time 16ns
• Path length 4.6m
• Momentum
• Pk1.5 GeV/c (?P/P1.4x10-4)
• Pp form (K, p) reaction (?P/P6.3x10-4)
• Present TOF
• ? 300ps w/o PHC
• Present BH1,2
• ? 200ps w/ PHC

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Beam Veto

• SAC efficiency 99
• ?5k trigger /spill _at_ 500k/spill
• SFV ?10 trigger
• Reduction of acceptance 7.5
• Beam size
• sx19.8mm
• sy3.2mm
• (u0.02, v0.002)

• SBS
• K- beam directly hit SDC3,4.
• ?
• Scattering beam particles by some material (Pb,
  W)
• 300kHz?60kHz _at_ 20mm cell

SBS
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3-body Decay
K-?p-p-p (5.58) K-?e-p0? (4.87) K-?µ-p0?
(3.27) K-?p-p0p0 (1.73)
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Muon Filter
Before

• 89 of µ can be detected in the trigger
• In the offline analysis 100
• Over kill for true p 1.7

After
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Muon Filter
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Iron thickness
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PiZero Veto
Before

• 70 of p0 can be detected by 2 set of 2cm lead
  plate and scintillation counter layer. (75 of ?
  from p0 hit the SP0)

After
Simulation in progress
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PiZero Veto
Beam K
Before

• 70 of p0 can be detected by 2 set of 2cm lead
  plate and scintillation counter layer. (75 of ?
  from p0 hit the SP0)

After
Simulation in progress
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Percentage of decay in target 25cm
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(No Transcript)
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? Hypernucleus

• strangeness S -1
• M1115.68 MeV
• Jp1/2
• I0
• Mean life263.2 ps

?
Nucleus
? hypernucleus
? hypernucleus ? ? is bound in a nucleus
N-N interaction ? B-B interaction
The Baryon which is different from nucleons (p/n)
Deeply bound in a nucleus w/o Pauli effect
The property of baryon changing in the nuclear
medium
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? Hypernucleus
N-N interaction ? B-B interaction
The Baryon which is different from nucleons (p/n)
Deeply bound in a nucleus w/o Pauli effect
The property of baryon changing in the nuclear
medium
? Hypernucleus ? ?N effective interaction
Systematic studies of several hypernuclei ? J-PARC
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Level scheme of 7?Li
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Calculated cross section for 7?Li
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B(M1) mesurement