Download - ハイパー核ガンマ線分光用 磁気スペクトロメータ -SksMinus-
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ハイパー核ガンマ線分光用磁気スペクトロメータ
-SksMinus-
東北大学 大学院理学研究科白鳥昂太郎
12/14 @ ATAMI
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2006 Strangeness ATAMI 2
Outline
Background of experiments Requirement on setup Modification of SKS Setup : SksMinus Detectors in detail, DC, Veto counters Summary Future plan
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2006 Strangeness ATAMI 3
“DAY-1” experiment E13
Several light hypernuclear gamma-ray spectroscopy experiments are planned.
(4He, 7
Li, 10B, 11
B, 19F)
Beam momentum (K-, - ) @ 1.5 GeV/c (500 k/spill, full intensity)The best sensitivity for selecting spin-flip state1.1~1.8 GeV/c beam for 4He
n
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2006 Strangeness ATAMI 4
Requirement on spectrometer forhypernuclear gamma-ray spectroscopy
To analyze 1.4 GeV/c (1.1~1.8 GeV/c) scattered - by existing spectrometer system
Large acceptance ~100 msr, ~20 degree
→ Enough hypernuclear production yield. Good momentum resolution 2~4 MeV/c→ To distinguish excited states of hypernuclei
SksMinus(Superconducting Kaon Spectrometer Modified for Hypernuclear Gamma ray Spectroscopy)
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SKS to SksMinus
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2006 Strangeness ATAMI 6
The modification of SKS
Momentum resolution0.1%FWHM (0.72 MeV/c)
@ 720 MeV/c, 2.2T
Maximum central momentum
1.0 GeV/c @ 2.7T
Acceptance 100 msr @ 0.72GeV/c
2.2T 2.7T
~20° ~20°
Scattered particles are not focused and present drift chambers (SDC3,4) are small for large reaction angle (half acceptance).
1.05 GeV/c (+, K+) reaction (K+ 0.72 GeV/c)
Present SKS
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2006 Strangeness ATAMI 7
The modification of SKS Keeping large acceptance and wide angular coverage by large drift chambers (2m×1m) (from BNL and Freiburg)
Incident beam angle and position of drift chambers are optimized by keeping acceptance for the 1.5 GeV/c beam condition.
Setup can be used for 1.1~1.8 GeV/c beam hypernuclear gamma ray spectroscopy experiment without modification.
~20°
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2006 Strangeness ATAMI 8
The modification of SKS Keeping large acceptance and wide angular coverage by large drift chambers (2m×1m) (from BNL and Freiburg)
Incident beam angle and position of drift chambers are optimized by keeping acceptance for the 1.5 GeV/c beam condition.
Setup can be used for 1.1~1.8 GeV/c beam hypernuclear gamma ray spectroscopy experiment without modification.
170cm
270cm
On the step, not a giant
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2006 Strangeness ATAMI 9
The K1.8 Beam line and SksMinusBeam spectrometer
・ BH1,2 : Time-of
-flight
・ BAC : - veto (n=1.03)SksMinus
・ STOF : Time-of-flight
・ SAC : K- beam veto (n=1.03)
・ SFV : K- beam vetoTarget : ~ 20 g/cm2
Length : 20 cmMWPC & DC: Beam position measurement
Background Veto
・ SMF : - from K- → - +
・ SP0 : - from K- → - +
0
Hyperball-J : ray
T.Koike 12/15
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2006 Strangeness ATAMI 10
SksMinus
SksMinus
・ SAC : K- beam veto (n=1.03)
・ SFV : K- beam veto・ STOF : Time-of-flight
SDC1~4: Beam position measurement
Background Veto
・ SMF : - from K- → - +
・ SP0 : - from K- → - +
0Target : ~20 g/cm2
Length : 20 cm
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SksMinus performanceBasic performance
Acceptance Momentum resolution
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2006 Strangeness ATAMI 12
Acceptance Acceptance at 1.4 GeV/c ~130 msr by large drift chambers (2m×1m) Angular acceptance is enough, ~ 20 degree
Acceptance is determined by SKS magnet gap and distance from SKS entrance. Higher momentum→ Cut off by SKS magnet Lower momentum→ Out of range SDC3,4
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2006 Strangeness ATAMI 13
Momentum resolution
Momentum resolution at 1.4 GeV/c ~2.1 MeV/c (FWHM) , intrinsic ~1.6, MSC ~1.3 400 m DC resolution and multiple scattering (DC : Ar gas, He bag : He gas, Air)
Higher momentum→ Intrinsic resolution (bending angle) Lowe momentum→ Similar to present SKS, ~0.9 MeV/c (FWHM) @ 1.0 GeV/c
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SksMinus performanceBeam decay suppression
Muon Filter PiZero Veto
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2006 Strangeness ATAMI 15
Background rejection
Beam K- decay products make serious background (Trigger rate, Missing mass spectrum)
Fake trigger ~1740/spillTrue event trigger ~1000/spill(Contribution of three-body decay ~200 /spill)
Beam K
BAC SACTarget20cm
Reaction
K- → - (63.4%)
⇒Muon Filter (1390 /spill) K- → - 0 (21.1%)
⇒PiZero Veto (350 /spill)
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2006 Strangeness ATAMI 16
Background rejection
K- → - (63.4%)
⇒Muon Filter (1390 /spill) K- → - 0 (21.1%)
⇒PiZero Veto (350 /spill)
Beam K- decay products make serious background (Trigger rate, Missing mass spectrum)
Fake trigger ~1740/spillTrue event trigger ~1000/spill(Contribution of three-body decay ~200 /spill)
Beam K
BAC SACTarget20cm
Decay
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2006 Strangeness ATAMI 17
Muon Filter -SMF-
86% of can be rejected in the trigger @ 1.5 GeV/c beam Stopped cannot be rejected. (In the offline analysis >99%) Over kill for true π ~2.5%
- (passing through)- (stopped in the iron)
Not need to change iron thickness, 1.1~1.8 GeV/c beam
momentum
Stopping points
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2006 Strangeness ATAMI 18
Muon Filter -SMF-
86% of can be rejected in the trigger @ 1.5 GeV/c beam Stopped cannot be rejected. (In the offline analysis >99%) Over kill for true π ~2.5%
Not need to change iron thickness, 1.1~1.8 GeV/c beam
momentum
Stopping points
-
-
X
Z
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2006 Strangeness ATAMI 19
PiZero veto -SP0-
78% of 0 can be detected by 6 sets of 5 mm lead plate and scintillation counter layer at 1.5 GeV/c beam. (85% of from 0 hit the SP0)
Reaction - pass through the window.
Acceptance 85%
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2006 Strangeness ATAMI 20
PiZero veto -SP0-
78% of 0 can be detected by 6 sets of 5 mm lead plate and scintillation counter layer at 1.5 GeV/c beam. (85% of from 0 hit the SP0)
Reaction - pass through the window.
Acceptance 85%
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2006 Strangeness ATAMI 21
Trigger rate @ 1.5 GeV/c beam
(K-,π-) Reaction rate ~1000 /spill K-→- ~1390 /spill K-→- 0 ~350 /spill K- Beam ~30 /spill 3-body decay ~200 /spill
~2970 /spillw/o Veto counters
True trigger ~500 /spillw/ Ge trigger and fake trigger greatly decreased (1/4).
~1320/spillw/ Veto counters
~570/spillw/ Ge trigger
(K-, - ) at pK = 1.5 GeV/c (500 k/spill)
Comparable to the present trigger rate
(K-,π-) Reaction rate ~950 /spill K-→- ~190 /spill K-→- 0 ~80 /spill K- Beam ~30 /spill 3-body decay ~70 /spill
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2006 Strangeness ATAMI 22
4He experiment
Energy spacing of 4He(1+) → 4
He(0+), (4H(1+)
→ 4H(0+) : (K-, 0 ), no charge and SP0 ?)
@ 1.5 GeV/c beam M.Ukai 12/15
Spin-flip measurement• Momentum (1.1), 1.3, 1.5, 1.8 GeV/c→Acceptance and momentum resolution are enough.• PID counters→STOF, SAC and SFV are enough.• Veto counters→More study is needed : Trigger rate @ 1.8 GeV/c.
n
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2006 Strangeness ATAMI 23
Summary Several hypernulcear gamma-ray experiments are
planned at the J-PARC K1.8 beam line (4He, 7
Li, 10
B, 11B, 19
F).
SksMinus is sufficient for hypernuclear gamma-ray spectroscopy at 1.5 GeV/c beam. Acceptance 130 msr, 20 degree. Momentum resolution 2.1 MeV/c.
Simulations in progress show a good veto counter efficiency at 1.5 GeV/c beam, SMF ~86%, SP0 ~78%.
SksMinus can be used for 1.1~1.8 GeV/c beam.
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2006 Strangeness ATAMI 24
Future Plan
Determination of the final SksMinus design SDC3&4 shipped from BNL and Freiburg and
repaired in 2007 PMT for TOF and Cherenkov from BNL D6
beam line and Range counter (E559) in 2007 Design and construction of SMF, SP0 and
other counters in 2007~2008
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Backup
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2006 Strangeness ATAMI 26
Particle identification (K-, - ) → - or K-
Beam K- can greatly be decreased by SAC (n=1.03) and SFV→ less than 30 trigger /spill (500 k/spill beam)
Time resolution of STOF ~150 ps (rms) For B(M1) measurement, dual SAC is planned because of saving forward events.
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2006 Strangeness ATAMI 27
Magnetic field
Calculated magnetic filed map is used in simulations.
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2006 Strangeness ATAMI 28
The modification of SKSLarge acceptance and wide angular coverage by large drift chambers (2m×1m)
Incident beam angle and position of drift chambers are optimized by keeping acceptance for the 1.5 GeV/c beam condition.
Setup can be used for 1.1~1.8 GeV/c beam hypernuclear gamma ray spectroscopy experiment without modification.
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2006 Strangeness ATAMI 29
Beam VetoSAC efficiency ~ 99%→5k trigger /spill @ 500k/spill
SFV → ~ 10 trigger Reduction of acceptance 7.5%
Beam size σx=19.8 mmσy=3.2 mm(u=0.02, v=0.002)
SBS
SBSK- beam directly hit SDC3,4.↓Scattering beam particles by some material (Pb, W)300kHz → 60kHz @ 20mm cell
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2006 Strangeness ATAMI 30
SMF & SP0 performance @ 1.1~1.8 GeV/c beam
It is difficult to suppress trigger rate at higher beam intensity…
- ~580 trigger/spill @ 1.8 GeV/c beam(~4300 trigger)
- ~360 trigger/spill @ 1.8 GeV/c beam(~1200 trigger)
SMF SP0
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2006 Strangeness ATAMI 31
3-body Decay
K-→π-π-π+ (5.58%)K-→e-π0ν (4.87%)K-→μ-π0ν (3.27%)K-→π-π0π0 (1.73%)