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SKS spectrometer system for J-PARC experiments

SKS spectrometer system for J-PARC experiments. J-PARC experiment with SKS. SksJ ? (SksJ + , SksJ - , SksJ 0 ). Detector configuration. Detector elements. Base. Additional. SksMinus (SksJ - ). SAC, SMF, SP0, Iron block. SksPlus (SksJ + ). D magnet, AC, TOF2, DC3, (WC). SksZero

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SKS spectrometer system for J-PARC experiments

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  1. SKS spectrometer system for J-PARC experiments

  2. J-PARC experiment with SKS SksJ ? (SksJ+, SksJ-, SksJ0)

  3. Detector configuration

  4. Detector elements Base Additional SksMinus (SksJ-) SAC, SMF, SP0, Iron block SksPlus (SksJ+) D magnet, AC, TOF2, DC3, (WC) SksZero (SksJ0) AC, LC SKS magnet SDC : Drift chamber TOF : Timing counter (+each He Bag)

  5. SksMinus SKS magnet SDC : Drift chamber TOF : Timing counter ⇒Same as Base +SAC,SMF,SP0 • Optimized for the (K-, p-) @ pK=1.5 GeV/c • Beam angle ~40°

  6. SksPlus original SKS magnet SDC : Drift chamber TOF : Timing counter ⇒Same as Base +D magnet : 900 mm from SKS DC3 between SKS and D AC and TOF2(same as SMF) • Beam angle ~45° • Acceptance is determined by TOF and AC.

  7. SksPlus SKS magnet SDC : Drift chamber TOF : Timing counter ⇒Same as Base +D magnet : 900 mm from SKS DC3 between SKS and D AC and TOF2(same as SMF) • Beam angle ~45° • Acceptance is determined by TOF and AC.

  8. SksZero original • SKS magnet • SDC : Drift chamber • TOF : Timing counter • ⇒Just rotated base detectors and the relative position is the same as Base. • Tile angle is the same as previous SKS. • +AC and LC • Beam angle ~40° • The detectors are just enlarged.

  9. SksZero • SKS magnet • SDC : Drift chamber • TOF : Timing counter • ⇒Just rotated base detectors and the relative position is the same as Base. • Tile angle is the same as previous SKS. • +AC and LC • Beam angle ~40° • The detectors are just enlarged. • Path length: 5.7 m → 6.2 m 65 % → 68 % decay @ 0.72 GeV/c ⇒ 3 % decay factor increased

  10. Acceptance

  11. Magnetic field selection Acceptance is estimated taking into account the lack of the measured magnetic filed map. • Region cut • To select events which path through inside of the region shown in right figure • z-direction ±220 mm (magnet gap ±250 mm) Y X Z

  12. SKS Acceptance • The simulated result is almost consist with the previous result. ~105 msr (100 msr). • Absolute values is little larger than previous result. ⇒Size of SDCIn • The acceptance of lower momentum is smaller. ⇒AC position 2.2 T Map

  13. SksMinus acceptance Requirements • (K-, p-) reaction @ 1.5 GeV/c ⇒ 1.4 GeV/c scattered particles • 1.0-1.7 GeV/c for 4He experiment • Acceptance is as large as possible. (K-, p-) Comments • Region cut decreases the acceptance but in the case of SksMinus, we can use the region if the momentum resolution is acceptable (< 4MeV/c). ○ : No cut × : Region cut □ : Region cut only z-direction (±220 mm cut)

  14. SksPlus acceptance Requirements • (K-, K+) reaction @ 1.8 GeV/c ⇒ 1.1-1.4 GeV/c scattered particles • For high momentum proton background, the acceptance is cut off below ~1.5 GeV/c. X Comments • Absolute values of acceptance is determined by the gap size of the D magnet, ~ 40 msr. • To reduce the acceptance of scattered particles of more than 1.5 GeV/c, the optimization of acceptance is needed. ○ : New SksPlus × : Previous SksPlus

  15. SksPlus acceptance Requirements • (K-, K+) reaction @ 1.8 GeV/c ⇒ 1.1-1.4 GeV/c scattered particles • For high momentum proton background, the acceptance is cut off below ~1.5 GeV/c. qsct.<10° X Comments • Absolute values of acceptance is determined by the gap size of the D magnet, ~ 40 msr. • To reduce the acceptance of scattered particles of more than 1.5 GeV/c, the optimization of acceptance is needed. ○ : New SksPlus × : Previous SksPlus

  16. SksZero acceptance Requirements • (p-, K+) reaction @ 1.2 GeV/c ⇒ 0.8-0.9 GeV/c scattered particles • p(p-, K+)S- reaction @ 1.2 GeV/c ⇒ 0.6-0.7 GeV/c scattered particles • (p+, K+) reaction @ 1.05 GeV/c ⇒ 0.63-0.73 GeV/c scattered particles • p(p-, K-)Q+ reaction @ 1.87, 1.92,1.97 GeV/c ⇒ 0.7-0.95 GeV/c scattered particles S DCX (p+, K+) Q ○ : 2.2 T Map × : 2.4 T Map (2.7 T map scaled) □ : 2.7 T Map Comments • DCX, (p+, K+) ⇒ 2.2 T • Q search ⇒ 2.4 T

  17. SksZero acceptance Requirements • (p-, K+) reaction @ 1.2 GeV/c ⇒ 0.8-0.9 GeV/c scattered particles • p(p-, K+)S- reaction @ 1.2 GeV/c ⇒ 0.6-0.7 GeV/c scattered particles • (p+, K+) reaction @ 1.05 GeV/c ⇒ 0.63-0.73 GeV/c scattered particles • p(p-, K-)Q+ reaction @ 1.87, 1.92,1.97 GeV/c ⇒ 0.7-0.95 GeV/c scattered particles qsct.<15° S DCX (p+, K+) Q ○ : 2.2 T Map × : 2.4 T Map (2.7 T map scaled) □ : 2.7 T Map Comments • DCX, (p+, K+) ⇒ 2.2 T • Q search ⇒ 2.4 T

  18. Momentum resolution

  19. Simulation condition Simulation condition • Region cut • DC resolution (rms) SksMinus : In&Out 400 mm SksPlus : In 300 mm, Out 400 mm SksZero : In 300 mm, Out 400 mm • Multiple scattering ⇒DC:Ar gas, He bag, other:Air • He bag ⇒SKS inside, between SDC3 and SDC4, between SKS and SDC3 He bag Out In Drift chamber

  20. SKS Momentum resolution • The simulated result is too good. 0.70 MeV/c(FWHM) @ 0.72 GeV/c ⇒ ~1.2 MeV/c(FWHM) for real date with the beam spectrometer resolution 0.70 MeV/c(FWHM) @ 0.72 GeV/c 2.2 T Map

  21. SksMinus momentum resolution • The momentum resolution is little worse. 2.3 MeV/c(FWHM) @ 1.4 GeV/c ⇒ 2.1 MeV/c(FWHM) for previous simulations 2.3 MeV/c(FWHM) @ 1.4 GeV/c 2.7 T Map

  22. SksPlus momentum resolution • The momentum resolution is 1.8 MeV/c(FWHM) @ 1.35 GeV/c ⇔ 2.1 MeV/c(FWHM) for previous SksPlus ∵ Degree of freedom of x direction is increased. 1.8 MeV/c(FWHM) @ 1.35 GeV/c X 2.7 T Map ○ : Previous SksPlus × : SksPlus

  23. SksZero momentum resolution • The momentum resolution is 0.69 MeV/c(FWHM) @ 0.72 GeV/c ⇔ 0.70 MeV/c(FWHM) for previous SKS • If the momentum resolution is twice worse, the resolution is less than 3 MeV/c. 0.9 MeV/c(FWHM) @ 0.69 GeV/c S DCX (p+, K+) 2.2 T Map ○ : Previous SKS × : SksZero

  24. SksZero momentum resolution • The momentum resolution is 0.69 MeV/c(FWHM) @ 0.72 GeV/c ⇔ 0.70 MeV/c(FWHM) for previous SKS • If the momentum resolution is twice worse, the resolution is less than 3 MeV/c. Q S DCX (p+, K+) ○ : SksZero 2.2 T Map × : SksZero 2.4 T Map (2.7 T Map scaled) □ : SksZero 2.7 T Map

  25. Summary • SksPlus performance with detectors of at the downstream of SksMinus satisfies the experimental requirements, flat acceptance, 1.1-1.4 GeV/c and better momentum resolution, 1.8 MeV/c(FWHM). • SksZero performance satisfies the all requirements of DCX, normal (p+, K+) and Q search experiment. • It is possible to construct the spectrometer system “SksJ ?” by using the same detector elements.

  26. Problem (for SksZero) • Beam through • The beam directly hits the down stream detectors by using the (p+, K+) reaction. • Trigger rate and background events • Acceptance is increased ⇒ Accepted background events are increased. • For DCX and Q search experiment, the beam hits the SKS magnet and makes the large background.

  27. Beam through • The beam hits the down stream detectors by the (p+, K+) reaction at pp=1.05 GeV/c • The setup of SksZero is not optimized to avoid the beam through. 1.05 GeV/c

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