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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-

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. Outline. Background of experiments Requirement on setup Modification of SKS Setup : SksMinus Detectors in detail, DC, Veto counters Summary Future plan. “DAY-1” experiment E13.

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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-

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  1. ハイパー核ガンマ線分光用磁気スペクトロメータ-SksMinus-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

  2. Outline • Background of experiments • Requirement on setup • Modification of SKS • Setup : SksMinus • Detectors in detail, DC, Veto counters • Summary • Future plan 2006 Strangeness ATAMI

  3. “DAY-1” experimentE13 • Several light hypernuclear gamma-ray spectroscopy experiments are planned. (4LHe, 7LLi, 10LB, 11LB, 19LF) Beam momentum • (K-, p-g) @ 1.5 GeV/c (500 k/spill, full intensity) • The best sensitivity for selecting spin-flip state • 1.1~1.8 GeV/c beam for 4LHe K- + n-> L + p- 2006 Strangeness ATAMI

  4. Requirement on spectrometer forhypernuclear gamma-ray spectroscopy • To analyze 1.4 GeV/c (1.1~1.8 GeV/c) scattered p- byexistingspectrometer system • Large acceptance ~100 msr, q~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) 2006 Strangeness ATAMI

  5. SKS to SksMinus

  6. The modification of SKS Present SKS 2.2T 2.7T q~20° q~20° 1.05 GeV/c (p+, K+) reaction (K+ 0.72 GeV/c) • Scattered particles are not focused and present drift chambers (SDC3,4)are small for large reaction angle (half acceptance). 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. q~20° 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. On the step, not a giant 270cm 170cm 2006 Strangeness ATAMI

  9. The K1.8 Beam line and SksMinus Beam spectrometer ・BH1,2 : Time-of -flight ・BAC : p- veto (n=1.03) SksMinus ・STOF : Time-of-flight ・SAC : K- beam veto (n=1.03) ・SFV : K- beam veto Target : ～20 g/cm2 Length : 20 cm MWPC & DC : Beam position measurement Background Veto ・SMF : m- from K- → m- + n ・SP0 : p- from K- → p- + p0 Hyperball-J : g ray T.Koike 12/15 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 : m- from K- → m- + n ・SP0 : p- from K- → p- + p0 Target : ~20 g/cm2 Length : 20 cm 2006 Strangeness ATAMI

  11. SksMinus performanceBasic performance Acceptance Momentum resolution

  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 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 mm 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 2006 Strangeness ATAMI

  14. SksMinus performanceBeam decay suppression Muon Filter PiZero Veto

  15. Target 20cm BAC SAC p Beam K Reaction Background rejection Beam K- decay products make serious background (Trigger rate, Missing mass spectrum) • K- → m-n (63.4%) ⇒Muon Filter(1390 /spill) • K- → p- p0 (21.1%) ⇒PiZero Veto (350 /spill) Fake trigger ~1740/spill True event trigger ~1000/spill (Contribution of three-body decay ~200 /spill) 2006 Strangeness ATAMI

  16. Target 20cm BAC SAC m Beam K Decay n Background rejection Beam K- decay products make serious background (Trigger rate, Missing mass spectrum) • K- → m- n (63.4%) ⇒Muon Filter(1390 /spill) • K- → p- p0 (21.1%) ⇒PiZero Veto (350 /spill) Fake trigger ~1740/spill True event trigger ~1000/spill (Contribution of three-body decay ~200 /spill) 2006 Strangeness ATAMI

  17. Muon Filter -SMF- Stopping points p- (stopped in the iron) m momentum m- (passing through) • 86% of m can be rejectedin the trigger @ 1.5 GeV/c beam • Stopped m 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 2006 Strangeness ATAMI

  18. Muon Filter -SMF- Stopping points X m- Z p- m momentum • 86% of m can be rejectedin the trigger @ 1.5 GeV/c beam • Stopped m 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 2006 Strangeness ATAMI

  19. PiZero veto -SP0- Acceptance 85% • 78% of p0 can be detected by 6 sets of 5 mm lead plate and scintillation counter layer at 1.5 GeV/c beam. (85% of g from p0 hit the SP0) Reaction p- pass through the window. 2006 Strangeness ATAMI

  20. PiZero veto -SP0- Acceptance 85% • 78% of p0 can be detected by 6 sets of 5 mm lead plate and scintillation counter layer at 1.5 GeV/c beam. (85% of g from p0 hit the SP0) Reaction p- pass through the window. 2006 Strangeness ATAMI

  21. Trigger rate @ 1.5 GeV/c beam (K-, p- g) at pK = 1.5 GeV/c (500 k/spill) • (K-,π-) Reaction rate ~1000 /spill • K-→m- n ~1390 /spill • K-→p- p0 ~350 /spill • K- Beam ~30 /spill • 3-body decay ~200 /spill ~2970 /spill w/o Veto counters True trigger ~500 /spill w/ Ge trigger and fake trigger greatly decreased (1/4). • (K-,π-) Reaction rate ~950 /spill • K-→m- n~190 /spill • K-→p- p0~80 /spill • K- Beam ~30 /spill • 3-body decay ~70 /spill ~1320/spill w/ Veto counters ~570/spill w/ Ge trigger Comparable to the present trigger rate 2006 Strangeness ATAMI

  22. 4LHe experiment • Energy spacing of 4LHe(1+) → 4LHe(0+), (4LH(1+) → 4LH(0+) : (K-, p0 ), 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. K- + n-> L + p- 2006 Strangeness ATAMI

  23. Summary • Several hypernulcear gamma-ray experiments are planned at the J-PARC K1.8 beam line (4LHe, 7LLi, 10LB, 11LB, 19LF). • 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. 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 2006 Strangeness ATAMI

  25. Backup

  26. Particle identification • (K-, p- ) → p- 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. 2006 Strangeness ATAMI

  27. Magnetic field Calculated magnetic filed map is used in simulations. 2006 Strangeness ATAMI

  28. The modification of SKS • Large 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. 2006 Strangeness ATAMI

  29. Beam Veto • SAC efficiency ～99% →5k trigger /spill @ 500k/spill SFV →～10 trigger Reduction of acceptance 7.5% • Beam size σx=19.8 mm σy=3.2 mm (u=0.02, v=0.002) • SBS K- beam directly hit SDC3,4. ↓ Scattering beam particles by some material (Pb, W) 300kHz → 60kHz@ 20mm cell SBS 2006 Strangeness ATAMI

  30. SMF & SP0 performance @ 1.1~1.8 GeV/c beam SMF SP0 m- ~580 trigger/spill @ 1.8 GeV/c beam (~4300 trigger) p- ~360 trigger/spill @ 1.8 GeV/c beam (~1200 trigger) It is difficult to suppress trigger rate at higher beam intensity… 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%) 2006 Strangeness ATAMI

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