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 ATAMI

2006 Strangeness ATAMI2 Outline  Background of experiments  Requirement on setup  Modification of SKS  Setup : SksMinus  Detectors in detail, DC, Veto counters  Summary  Future plan

2006 Strangeness ATAMI3 “DAY-1” experiment E13  Several light hypernuclear gamma-ray spectroscopy experiments are planned. ( 4  He, 7  Li, 10  B, 11  B, 19  F) Beam momentum  (K -,  -  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 4  He    n  

2006 Strangeness ATAMI4 Requirement on spectrometer for hypernuclear 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)

SKS to SksMinus

2006 Strangeness ATAMI6 The modification of SKS Momentum resolution 0.1%FWHM ( MeV/c, 2.2T Maximum central momentum T Acceptance GeV/c 2.2T2.7T  ~20°  Scattered particles are not focused and present drift chambers (SDC3,4) are small for large reaction angle (half acceptance) GeV/c (  +, K + ) reaction (K GeV/c) Present SKS

2006 Strangeness ATAMI7 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°

2006 Strangeness ATAMI8 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

2006 Strangeness ATAMI9 The K1.8 Beam line and SksMinus Beam 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 veto Target : ～ 20 g/cm 2 Length : 20 cm MWPC & DC : Beam position measurement Background Veto ・ SMF :  - from K - →  - + ・ SP0 :  - from K - →  - +  0 Hyperball-J :  ray T.Koike 12/15

2006 Strangeness ATAMI10 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 - →  - +  0 Target : ~20 g/cm 2 Length : 20 cm

SksMinus performance Basic performance  Acceptance  Momentum resolution

2006 Strangeness ATAMI12 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 ATAMI13 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 1.0 GeV/c

SksMinus performance Beam decay suppression  Muon Filter  PiZero Veto

2006 Strangeness ATAMI15 Background rejection Beam K - decay products make serious background (Trigger rate, Missing mass spectrum) Fake trigger ~1740/spill True event trigger ~1000/spill (Contribution of three-body decay ~200 /spill) Beam K BACSAC Target 20cm  Reaction  K - →  - (63.4%) ⇒ Muon Filter (1390 /spill)  K - →  -  0 (21.1%) ⇒ PiZero Veto (350 /spill)

2006 Strangeness ATAMI16 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/spill True event trigger ~1000/spill (Contribution of three-body decay ~200 /spill) Beam K BACSAC Target 20cm  Decay

2006 Strangeness ATAMI17 Muon Filter -SMF-  86% of  can be rejected in the 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

2006 Strangeness ATAMI18 Muon Filter -SMF-  86% of  can be rejected in the 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

2006 Strangeness ATAMI19 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%

2006 Strangeness ATAMI20 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%

2006 Strangeness ATAMI21 Trigger 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 /spill w/o Veto counters True trigger ~500 /spill w/ Ge trigger and fake trigger greatly decreased (1/4). ~1320/spill w/ Veto counters ~570/spill w/ Ge trigger (K -,  -  ) at p K = 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

2006 Strangeness ATAMI22 4  He experiment  Energy spacing of 4  He(1 + ) → 4  He(0 + ), ( 4  H(1 + ) → 4  H(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 1.8 GeV/c.    n  

2006 Strangeness ATAMI23 Summary  Several hypernulcear gamma-ray experiments are planned at the J-PARC K1.8 beam line ( 4  He, 7  Li, 10  B, 11  B, 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.

2006 Strangeness ATAMI24 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

Backup

2006 Strangeness ATAMI26 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.

2006 Strangeness ATAMI27 Magnetic field Calculated magnetic filed map is used in simulations.

2006 Strangeness ATAMI28 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 ATAMI29 Beam Veto  SAC efficiency ～ 99% →5k trigger 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 → 20mm cell

2006 Strangeness ATAMI30 SMF & SP0 1.1~1.8 GeV/c beam It is difficult to suppress trigger rate at higher beam intensity…  - ~ GeV/c beam (~4300 trigger)  - ~ GeV/c beam (~1200 trigger) SMFSP0

2006 Strangeness ATAMI31 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%)