1. Master thesis 2006 Shirotori1 Hypernuclear gamma-ray spectroscopy at J-PARC K1.8 beam line 東北大学大学院理学研究科 原子核物理 白鳥昂太郎

2. Master thesis 2006 Shirotori 2 Contents  Introduction  J-PARC facility & K1.8 beam line  Design of spectrometer : SksMinus  Background veto counters  Summary J-PARC

3. Master thesis 2006 Shirotori3 Introduction

4. Master thesis 2006 Shirotori 4  Hypernucleus  h ypernucleus →  is bound in a nucleus. Baryon other than nucleons (p/n) N-N interaction → B-B interaction Deeply bound in a nucleus w/o Pauli effect The possible change of baryon properties in the nuclear medium Nucleus  hypernucleus

5. Master thesis 2006 Shirotori 5 Investigation of  hypernuclei Systematic study at J-PARC Spin dependent interaction  Energy spacing of hypernuclei (~ a few 100 keV). → Only  -ray spectroscopy with germanium detectors (2-3keV) Spin flip B(M1) transition  g-factor of  in nuclear medium

6. Master thesis 2006 Shirotori 6 Hypernuclear  -ray spectroscopy experiment Missing mass analysis : magnetic spectrometers (identification of hypernuclear bound states ) Beam K - Scattered  -  -ray measurement by Ge detector array   rays from hypernuclei : Particle-  coincidence (  +, K +  ) @ KEK, (K -,  -  ) @ BNL Magnetic spectrometers + Hyperball (K -,  -  ) reaction @ J-PARC Optimized magnetic spectrometer + Hyperball-J Upgrade

7. Master thesis 2006 Shirotori 7 (K -,  - ) reaction Large production rate (/beam) Large elementary cross section, n (K -,  - )  : order of mb > n(  +, K + )  : ~10 2  b, p(e, e’K + )  : ~1  b Angular selectivity Small momentum transfer  5°~ 100 MeV/c :  L = 0  10°~ 200 MeV/c :  L = 1 or 2 @ 1.5 GeV/c beam Spin-flip cross section exists at large angles (  >10°). More advantages in hypernuclear  -ray spectroscopy experiment

8. Master thesis 2006 Shirotori 8 Day-1 experiment at J-PARC Several light hypernuclear  -ray spectroscopy experiments are planned. Beam momentum (K -,  -  ) @ 1.5 GeV/c Both spin-flip and spin-non-flip production    n    7  Li Spin-flip B(M1) measurement (g-factor of  in nuclear medium)  10  B, 11  B, 19  F Study of  N interaction  4  He (Beam momentum 1.1-1.8 GeV/c) Charge symmetry breaking of  N interaction Spin-flip property of  hypernuclear production

9. Master thesis 2006 Shirotori9 Experimental facility

10. Master thesis 2006 Shirotori 10 J-PARC & Hadron facility (Japan Proton Accelerator Research Complex) Very high intensity proton beam ~15  A →High intensity secondary hadronic beam ~10 M K - /spill (~50 times higher) Experimental setup has to meet the condition of K1.8 beam line. J-PARC Hadron experimental facility

11. Master thesis 2006 Shirotori 11 J-PARC & Hadron facility (Japan Proton Accelerator Research Complex) Experimental setup has to meet the condition of K1.8 beam line. Very high intensity proton beam ~15  A →High intensity secondary hadronic beam ~10 M K - /spill (~50 times higher) J-PARC

12. Master thesis 2006 Shirotori 12 K1.8 beam line K - beam @ 1.5 GeV/c 500 k/spill, full intensity (30 GeV, 9  A) (1400 k @ 1.8 GeV/c, 80 k @ 1.1 GeV/c) Beam spectrometer (QQDQQ)  Timing counter (BH1&BH2)  Aerogel cherenkov counter :  - veto (BAC)  MWPC and DC : Beam tracking (BC1~4)  p/p ~ 3.3×10 -4 (FWHM)

13. Master thesis 2006 Shirotori 13 Experimental setup  -ray measurement by Hyperball-J Missing mass analysis by magnetic spectrometer from (K -,  - ) events Hyperball-J Good magnetic spectrometer performance is necessary. +

14. Master thesis 2006 Shirotori14 Magnetic spectrometer -SksMinus-

15. Master thesis 2006 Shirotori 15 Spectrometer design from this work 1.Requirements 2.SksMinus elements : Detectors 3.Optimization 4.Basic performance  Acceptance  Momentum resolution 5.Design of veto counters and results of simulation  Beam-through  Beam decay

16. Master thesis 2006 Shirotori 16 Requirements for spectrometer  To analyze 1.4 GeV/c (1.1~1.8 GeV/c) scattered  - by existing spectrometer magnet  Large acceptance ~100 msr,  20 degree → Efficient tagging of hypernuclei and angular selectivity  Good momentum resolution 2  4 MeV/c (FWHM) → Identification of bound states of hypernuclei (mass resolution ~5 MeV (FWHM) ) Modified SKS (Superconducting Kaon Spectrometer) -SksMinus-

17. Master thesis 2006 Shirotori 17 SksMinus elements : Detectors  Drift chamber : momentum analysis  Timing counter  PID counters : Identification of (K -,  - ) reaction Aerogel Cherenkov counters K - beam veto counter (timing counter)  (Beam decay veto counters)

18. Master thesis 2006 Shirotori 18 Present SKS Momentum resolution 0.1%FWHM (0.72 MeV/c) @ 720 MeV/c, 2.2T Acceptance100 msr @ 0.72GeV/c Maximum central momentum 1.0 GeV/c @ 2.7T 1.05 GeV/c (  +, K + ) reaction (K + 0.72 GeV/c) 2.2T  scat ~20°  Incident beam direction  Size and placement of detectors at the exit of the SKS magnet

19. Master thesis 2006 Shirotori 19 Present SKS  scat ~20° 2.7T Momentum resolution 0.1%FWHM (0.72 MeV/c) @ 720 MeV/c, 2.2T Acceptance100 msr @ 0.72GeV/c Maximum central momentum 1.0 GeV/c @ 2.7T 1.05 GeV/c (  +, K + ) reaction (K + 0.72 GeV/c)  Incident beam direction  Size and placement of detectors at the exit of the SKS magnet

20. Master thesis 2006 Shirotori 20 Optimization Optimization of acceptance for the 1.5 GeV/c beam condition  Determination of incident beam angle (20 degree)  Adjustment of drift chamber position  Target distance (~80 cm) Performance (acceptance, momentum resolution) checked by the Geant4 simulation

21. Master thesis 2006 Shirotori 21 Simulation results of acceptance  Acceptance at 1.4 GeV/c, ~130 msr  Enough angular acceptance, ~20 degree

22. Master thesis 2006 Shirotori 22 Simulation results of momentum resolution Simulation condition :  DC resolution 400  m (rms)  Multiple scattering DC:Ar gas, He bag, other:Air Results :  Momentum resolution at 1.4 GeV/c ~2.1 MeV/c (FWHM) DC resolution ~1.6 MeV/c Multiple scattering ~1.3 MeV/c  Missing mass ~2.0 MeV (FWHM) Present SKS momentum resolution @ 0.72 GeV/c K -  Simulation ~0.8 MeV/c (FWHM)  Measured ~1.3 MeV/c (FWHM)

23. Master thesis 2006 Shirotori 23 SksMinus setup SksMinus  STOF : Time-of-flight  SAC : K - beam veto (n=1.03)  SFV : K - beam veto  SDC1~4 : Beam position measurement Background Veto  SMF :  - from K - →  - +  SP0 :  - from K - →  - +  0 _ Trigger = K in ×PI out  K in = BH1×BH2×BAC  PI out = STOF×SAC×SFV×SMF×SP0 Target ~20 g/cm 2

24. Master thesis 2006 Shirotori24 Background veto counters  Beam veto  Muon filter  PiZero veto

25. Master thesis 2006 Shirotori 25 Background events  True events : (K -,  - ) reaction  Fake events  Beam-through events  Beam decay  - (K - →  - )  - (K - →  -  0 ) _ Beam-through Beam decay

26. Master thesis 2006 Shirotori 26 Background events : Beam-through Rejection of Beam K - SAC (n=1.03) ~98% + SFV → Less than 30 trigger /spill (500 k/spill beam) STOF : Time resolution ~150 ps (rms) SAC SFV

27. Master thesis 2006 Shirotori 27 Background events : Beam decay  Trigger rate  Missing mass Fake trigger ~1940 /spill True event trigger ~600 /spill (Contribution of three-body decay ~200 /spill) Beam K BACSAC Target 20cm  Reaction  K - →  - (63.4%) (1390 /spill) ⇒ Muon Filter  K - →  -  0 (21.1%) (350 /spill) ⇒ PiZero Veto _

28. Master thesis 2006 Shirotori 28 Beam K BACSAC Target 20cm  Decay Background events : Beam decay Fake trigger ~1940 /spill True event trigger ~600 /spill (Contribution of three-body decay ~200 /spill) _  K - →  - (63.4%) (1390 /spill) ⇒ Muon Filter  K - →  -  0 (21.1%) (350 /spill) ⇒ PiZero Veto _  Trigger rate  Missing mass

29. Master thesis 2006 Shirotori 29 Muon Filter -SMF- design Stopping/absorption points Pass through Absorbed by

30. Master thesis 2006 Shirotori 30 Muon Filter -SMF- design -- -- 1 m Scattered particles SKS Iron Stopping/absorption points

31. Master thesis 2006 Shirotori 31 Muon Filter -SMF- design -- -- 1 m Scattered particles SKS Iron Stopping/absorption points

32. Master thesis 2006 Shirotori 32 Muon Filter -SMF- performance  Rejected  86%  Non-rejected (stopped in the iron) → offline analysis >99%  Over kill for true π ~2.5% Rejected Non-rejected Target SKS magnet Iron SMF Stopping/absorption points STOF

33. Master thesis 2006 Shirotori 33 PiZero veto -SP0- design  The total thickness of SP0 is limited < 16 cm.  E  = 60 ~ 1200 MeV : ~4 cm @ Pb Lead thickness & energy deposit

34. Master thesis 2006 Shirotori 34 PiZero veto -SP0- design  The total thickness of SP0 is limited < 16 cm.  E  = 60 ~ 1200 MeV : ~4 cm @ Pb Lead thickness & energy deposit

35. Master thesis 2006 Shirotori 35 PiZero veto -SP0- performance 78% of  -  0 events rejected 6 sets of 5 mm lead plate and 10 mm scintillation counter layer at 1.5 GeV/c beam. Acceptance 85%

36. Master thesis 2006 Shirotori 36 Background rejection and trigger rate ~470/spill w/ Ge trigger Comparable to the present trigger rate decay Total trigger is reduced by Ge trigger ~1/2. 7  Li bound states Offline analysis  (K -,π - ) Reaction rate : 600 ⇒ ~570  K - →  - : 1390 ⇒ ~190  K - →  -  0 : 350 ⇒ ~80  K - Beam : ~30  3-body decay : 200 ⇒ ~70  Total : 2570 (1940) ⇒ 940 (340) /spill

37. Master thesis 2006 Shirotori37 Summary

38. Master thesis 2006 Shirotori 38 Summary  Hypernuclear  -ray spectroscopy experiment (Day-1 experiment) at the J-PARC K1.8 beam line  Magnetic spectrometer designed  Optimization of setup  Acceptance ~130 msr  Angular coverage ~20 degree  Momentum resolution 2.1 MeV/c  Veto counters designed and performances checked  SMF : ~86%  -  events rejected  SP0 : ~78%  -  0 events rejected _ Feasibility proved by the present study Ready for construction

39. Master thesis 2006 Shirotori39 Backup

40. Master thesis 2006 Shirotori 40 4  He experiment  Charge symmetry breaking of  N interaction  4  H ⇔ 4  He (  n ⇔  p)  Both binging energy and energy spacing are different.  Statistics of old data is low.  Spin-flip property of  hypernuclear production  Important information for systematic study  Study of baryon production in nuclear medium  Beam momentum 1.1-1.8 GeV/c    n  

41. Master thesis 2006 Shirotori 41 Setup and Hyperball-J  -ray measurement by Hyperball-J (Total photo peak efficiency ~6% @ 1 MeV by Geant4 simulation) Missing mass analysis by magnetic spectrometer from (K -,  - ) events Hyperball-J Good magnetic spectrometer performance is necessary. Present study

42. Master thesis 2006 Shirotori 42 Choice of spectrometer Modified SKS (SksMinus) Name Accept. [msr] Resol. [MeV/c] Max. Mom. [GeV/c] SKS1001.0 SksPlus30  1.71.5 KURAMA20020  2.0 ×SksPlus : Acceptance is limited by the magnet gap. ×KURAMA: Momentum resolution is limited by bending power. △ SKS : Acceptance and maximum momentum are determined by geometry and detector size. → SKS can be usable by modification to the bending magnet.

43. Master thesis 2006 Shirotori 43 SKS to SksMinus Momentum resolution 0.1%FWHM (0.72 MeV/c) @ 720 MeV/c, 2.2T Acceptance100 msr @ 0.72GeV/c Maximum central momentum 1.0 GeV/c @ 2.7T 1.05 GeV/c (  +, K + ) reaction (K + 0.72 GeV/c) 2.2T  scat ~20° Present SKS  scat ~20° 2.7T

44. Master thesis 2006 Shirotori 44 Background rejection and trigger rate  (K -,π - ) Reaction rate : 600 ⇒ ~570  K - →  - : 1390 ⇒ ~190  K - →  -  0 : 350 ⇒ ~80  K - Beam : ~30  3-body decay : 200 ⇒ ~70  Total : 2570 (1940) ⇒ 940 (340) /spill Total trigger is reduced by Ge trigger ~1/2. ~470/spill w/ Ge trigger Comparable to the present trigger rate decay 7  Li bound states Offline analysis

45. Master thesis 2006 Shirotori 45 4  He experiment (Spin-flip measurement) p K = (1.1), 1.3, 1.5, 1.8 GeV/c  Acceptance and momentum resolution → Small loss of acceptance (1.1 and 1.8 GeV/c)  PID counters : STOF, SAC and SFV → Enough  Veto counters → SMF does not have to be changed. SP0 is fixed. → More study is needed : Trigger rate @ 1.8 GeV/c. SMF : 580 /spill, SP0 ; 360 /spill  momentum vs hit point The correlation between  momentum and hit position follows the same distribution.