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Hypernuclear gamma-ray spectroscopy at 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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2006 JPS in NARA2 Outline Background of experiments Requirement on setup Setup, SKS & Hyperball-J Detectors in detail, SKS & Veto counters Summary
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2006 JPS in NARA3 Previous hypernuclear gamma-ray experiments 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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2006 JPS in NARA4 Proposed “DAY-1” experiment E13 Several light hypernulcear gamma-ray spectroscopy experiments are planed. ( 4 Λ He, 7 Λ Li, 10 Λ B, 11 Λ B, 19 Λ F) (K -, π - γ) at p K = 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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2006 JPS in NARA5 HyperBall-J or HyperWall-J Wall TypeBall 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 >5% @ 1MeV (Geant4 simulation)
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2006 JPS in NARA6 Requirement on spectrometer for hypernuclear gamma-ray spectroscopy To analyze 1.4GeV/c-scattered π - by existing 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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2006 JPS in NARA7 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/cm 2 MWPC & DC : Beam position measurement Background Veto ・ SMF : μ - from K - →μ - +ν ・ SP0 : π - from K - →π - +π 0 Hyperball-J : γray Beam spectrometer SKS
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2006 JPS in NARA8 Present SKS to New SKS Momentum resolution 0.1%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 θ ~ 20° 2.2T 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.
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2006 JPS in NARA9 Present SKS to New SKS Momentum resolution 0.1%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 Parallel scattering 2.7T θ ~ 20° 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.
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2006 JPS in NARA10 Present SKS to New SKS 2.7T 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. θ ~ 20°
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2006 JPS in NARA11 Present SKS to New SKS SBS K - beam directly hit SDC3,4. ↓ Scattering beam particles by heavy material (Pb, W) 300kHz→60kHz/wire @ 20mm cell 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.
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2006 JPS in NARA12 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 - +π 0 Beam K π
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2006 JPS in NARA13 SKS Acceptance & Momentum resolution Acceptance ~ 120[msr] with large drift chambers (2[m]×1[m]) 100[msr] for present SKS Momentum resolution 2.1[MeV/c] (bending angle ~ 60° w/ multiple scattering) 0.8[MeV/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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2006 JPS in NARA14 Background rejection K - →μ - ν (63.4%) ⇒ Muon Filter K - →π - π 0 (21.1%) ⇒ PiZero Veto Beam K - decay products make serious background K - →π - π - π + (5.58%) K - →e - π 0 ν (4.87%) K - →μ - π 0 ν (3.27%) K - →π - π 0 π 0 (1.73%) Contribution is relatively small ~ 150 trigger Fake trigger ~ 1700/spill True event trigger ~ 700/spill Beam K BACSAC Target 20cm μ νDecay
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2006 JPS in NARA15 Muon Filter Thick Material (ex. Iron) μ-μ- π-π- Scintillation counter Scintillation counter Only μ- can be detected. Stopped by hadronic interaction Pass through
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2006 JPS in NARA16 Muon Filter After Before 89% of μ can be detected in the trigger In the offline analysis ~ 100% Over kill for true π ~ 1.7%
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2006 JPS in NARA17 PiZero Veto 70% of π 0 can be detected by 2 set of 2[cm] lead plate and scintillation counter layer. (75% of γ from π 0 hit the SP0) Simulation in progress Before After
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2006 JPS in NARA18 Trigger rate (K -,π - ) Reaction rate ~ 700/spill K - →μ - ν ~ 1320/spill K - →π - π 0 ~ 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. (K -,π - ) Reaction rate ~ 700/spill K - →μ - ν ~ 140/spill K - →π - π 0 ~ 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 p K = 1.5 GeV/c (500k/spill) Comparable to the present trigger rate
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2006 JPS in NARA19 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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2006 JPS in NARA21 Rough Kawazanyou (compared with BNL E930) 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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2006 JPS in NARA22 Proposed “DAY-1” experiment E13 Spin-flip B(M1) measurement and g Λ in a nucleus 7 Λ Li : Least ambiguities exist and most reliable ΛN interaction study from p-shell hypernuclei 10 Λ B and 11 Λ B : Inconsistency exists. Not enough experimental data Radial dependence of ΛN interaction from sd-shell hypernuclei 19 Λ F : Simplest in sd-shell Spin-flip property in hypernuclear production 4 Λ He : Easiest to observe a spin-flip state (K -, π - γ) at p K = 1.5 GeV/c (500k/spill)
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2006 JPS in NARA23 Beam Momentum n
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2006 JPS in NARA24 ΛN effective interaction V(r) = V 0 (r) + V (r) s N ・ s + V N (r) l N ・ s N + V (r) l N ・ s + V T (r) S 12 (Core nucleus : p-shell 、 Λ : s-shell) → Radial Integrals 、 S N 、 S 、 T are determined by previous experiments = 0.43 S N = -0.39 S = -0.01 T= 0.03 [MeV] Some inconsistencies appear ! Ex. 10 Λ 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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2006 JPS in NARA25 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 - +π 0 : SP0
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2006 JPS in NARA26 Time resolution Flight time ~ 16[ns] Path length ~ 4.6[m] Momentum P k =1.5 GeV/c (ΔP/P=1.4x10 -4 ) P π 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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2006 JPS in NARA27 Beam Veto SAC efficiency ~ 99% →5k trigger /spill @ 500k/spill SFV → ~ 10 trigger Reduction of acceptance 7.5% Beam size σ x =19.8[mm] σ y =3.2[mm] (u=0.02, v=0.002) SBS SBS K - beam directly hit SDC3,4. ↓ Scattering beam particles by some material (Pb, W) 300kHz→60kHz @ 20mm cell
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2006 JPS in NARA28 3-body Decay K - →π - π - π + (5.58%) K - →e - π 0 ν (4.87%) K - →μ - π 0 ν (3.27%) K - →π - π 0 π 0 (1.73%)
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2006 JPS in NARA29 Muon Filter 89% of μ can be detected in the trigger In the offline analysis ~ 100% Over kill for true π ~ 1.7% After Before
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2006 JPS in NARA30 Muon Filter
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2006 JPS in NARA31 Iron thickness
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2006 JPS in NARA32 PiZero Veto 70% of π 0 can be detected by 2 set of 2[cm] lead plate and scintillation counter layer. (75% of γ from π 0 hit the SP0) Simulation in progress After Before
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2006 JPS in NARA33 PiZero Veto 70% of π 0 can be detected by 2 set of 2[cm] lead plate and scintillation counter layer. (75% of γ from π 0 hit the SP0) Simulation in progress After Before Beam K
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2006 JPS in NARA34 Percentage of decay in target 25cm
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2006 JPS in NARA35
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2006 JPS in NARA36 Λ Hypernucleus Λ h ypernucleus → Λ is bound in a nucleus The Baryon which is different from nucleons (p/n) N-N interaction → B-B interaction Deeply bound in a nucleus w/o Pauli effect The property of baryon changing in the nuclear medium 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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2006 JPS in NARA37 Λ Hypernucleus The Baryon which is different from nucleons (p/n) N-N interaction → B-B interaction Deeply bound in a nucleus w/o Pauli effect The property of baryon changing in the nuclear medium Systematic studies of several hypernuclei → J-PARC Λ Hypernucleus ⇔ ΛN effective interaction
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2006 JPS in NARA38 Level scheme of 7 Λ Li
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2006 JPS in NARA39 Calculated cross section for 7 Λ Li
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2006 JPS in NARA40 B(M1) mesurement
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