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Setup for hypernuclear gamma-ray spectroscopy at the J-PARC K1.8 beam line

Setup for hypernuclear gamma-ray spectroscopy at the J-PARC K1.8 beam line. Department of Physics, Tohoku Univ. K. Shirotori for the Hyperball-J collaboration. Contents. Introduction Magnetic spectrometer : SksMinus g -ray detector array : Hyperball-J Summary. Introduction.

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Setup for hypernuclear gamma-ray spectroscopy at the J-PARC K1.8 beam line

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  1. Setup for hypernuclear gamma-ray spectroscopy at the J-PARC K1.8 beam line Department of Physics, Tohoku Univ. K. Shirotori for the Hyperball-J collaboration

  2. Contents • Introduction • Magnetic spectrometer : SksMinus • g-ray detector array : Hyperball-J • Summary K. Shirotori NP07 6/2

  3. Introduction

  4. E13 Day-1 experiment at J-PARC Several light hypernuclear g-ray spectroscopy experiments are planned. (4LHe,7LLi, 10LB, 11LB, 19LF) (K-, p- ) reaction @ pK = 1.5 GeV/c Hyperball-J Particle-g coincidence g-ray measurement Missing mass analysis Optimized magnetic spectrometer + Hyperball-J K. Shirotori NP07 6/2

  5. Magnetic spectrometer -SksMinus-

  6. Previous SKS setup • Incident beam direction • Size and placement of detectors at the exit of the SKS magnet 2.2T qscat~20° 1.05 GeV/c (p+, K+) reaction (K+ 0.72 GeV/c) K. Shirotori NP07 6/2

  7. Previous SKS setup • Incident beam direction • Size and placement of detectors at the exit of the SKS magnet 2.7T qscat~20° 1.05 GeV/c (p+, K+) reaction (K+ 0.72 GeV/c) K. Shirotori NP07 6/2

  8. SksMinus setup For the beam condition • Determination of incident beam angle (20 degree) • Larger drift chamber 2.7T qscat~20° 1.05 GeV/c (p+, K+) reaction (K+ 0.72 GeV/c) K. Shirotori NP07 6/2

  9. SksMinus setup (K-, p- ) reaction @ pK = 1.5 GeV/c ⇒Analyze 1.4 GeV/c p- Requirements • Acceptance >100 msr, ~20o scattering angles • Momentum resolution < 4 MeV/c (FWHM) SDC1~4 : Drift chambers STOF : TOF counter SAC : Aerogel Cherenkov counter Beam decay background veto _ • SMF : m- from K- → m- + n • SP0 : p- from K- → p- + p0 Target ~20 g/cm2 1 m K. Shirotori NP07 6/2

  10. Drift chamber and TOF counter To keep the large acceptance BD and BT from BNL are used as SDC3&4 and STOF, respectively. BD BD1 BD2 BT 48D48 Magnet 270 cm 170 cm Ajimura-san BNL-AGS D6 line K. Shirotori NP07 6/2

  11. Simulation results of acceptance and momentum resolution • Acceptance at 1.4 GeV/c, ~130 msr • Enough angular acceptance, ~20 degree • Momentum resolution at 1.4 GeV/c ~2.1 MeV/c (FWHM) K. Shirotori NP07 6/2

  12. Target 20cm BAC SAC m Beam K Decay Background events : Beam decay • Trigger rate • Missing mass _ K- → m-n (63.4%) ⇒Muon Filter K- → p- p0 (21.1%) ⇒PiZero Veto Overlap _ K. Shirotori NP07 6/2

  13. Beam decay veto counters Muon Filter γ p- (absorbed in the iron) m- (passing through) 86%of m-n events detected Others rejected (stopped in the iron) by offline analysis Totally > 99.9 % • Over kill for true π ~2.5% 80% of p-p0 events detected 10 sets of 3 mm lead plate and 8 mm scintillation counter layer at 1.5 GeV/c beam. Sufficient performance to reduce the trigger rate and background K. Shirotori NP07 6/2

  14. Hyperball-J

  15. Hyperball-J Severe radiation damage High counting rate at J-PARC • Mechanical cooler • PWO background suppressor • Waveform readout Simulated efficiency by Geant4 Hyperball-J (half) ~6% photo peak efficiency @ 1 MeV K. Shirotori NP07 6/2

  16. R&D in KEK and Tohoku Univ. Cooling power Ge crystal temperature less than 85K when biased Low mechanical vibration for 2 keV energy resolution Minimization of microphonics noise New Ge detector with Mechanical cooling 13 cm Cooler Ge 10 cm Mechanical cooler ⇒Suppression of the radiation damage effect with Ge crystal below 85 K (Liquid nitrogen cooling ~90 K) Ge Achieved K. Shirotori NP07 6/2 Compressor

  17. Background suppressor : PbWO4 The PWO crystal has very first decay constant ~6 ns. (~300 ns for BGO) But small light yield (PWO/BGO=1/10) • Doped PWO crystal • Cooling of PWO below 0℃ Ge energy spectrum 1 MeV g ray (simulation) -type U-type W-type L-type PWO suppression for g ray spectroscopy is possible. K. Shirotori NP07 6/2

  18. 10 V Waveform readout Pulse height ADC ⇒ Sampling ADC (waveform digitization) (after shaping) To improve energy resolution and recover rejected events at high counting rates • Baseline shift restoration • Pile-up signal decomposition Baseline Preamp output After shaping K. Shirotori NP07 6/2

  19. Waveform readout Pulse height ADC ⇒ Sampling ADC (waveform digitization) (after shaping) To improve energy resolution and recover rejected events at high counting rates • Baseline shift restoration • Pile-up signal decomposition No baseline restoration In the LNS test experiment, the positron beam is irradiated to Ge detector to make frequent baseline shits by reset signal. ⇒The restoration of the baseline shits 3.7 keV⇒ 3.1 keV (FWHM) (2.6 keV w/o beam) Baseline restoration 60Co 1.3 MeV g-ray spectrum K. Shirotori NP07 6/2

  20. Summary

  21. Summary • J-PARC E13 experiment by the (K-, p-) reaction @ pK =1.5 GeV/c • Optimal magnetic spectrometer • New Hyperball system for the high counting rate • Magnetic spectrometer, SksMinus and newly constructed array, Hyperball-J SksMinus performance • More than 100 msr acceptance and 20 degree coverage • ~2 MeV/c momentum resolution Hyperball-J • ~6 % efficiency • Mechanical cooling system • PWO counter • Waveform readout The experiment will be performed in 2009. K. Shirotori NP07 6/2

  22. Backup

  23. Particle identification Reaction ID by BAC and SAC (n=1.03) @ trigger Rejection of K- beam through background SAC ~98% + Beam veto (SFV) STOF : Time resolution ~150 ps (rms) SAC BAC Beam veto (SFV) K. Shirotori NP07 6/2

  24. (K-, p-) reaction Large production rate (/beam) Large elementary cross section, n(K-, p-)L : order of mb > n(p+, K+)L : ~102mb, p(e, e’K+)L : ~1 mb Large sticking probability Angular selectivity Small momentum transfer q~5°~ 100 MeV/c : DL = 0 q~10°~ 200 MeV/c : DL = 1 or 2 @ 1.5 GeV/c beam Spin-flip cross section exists at large angles (q >10°). More advantages in hypernuclear g-ray spectroscopy experiment K. Shirotori NP07 6/2

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