SKS spectrometer system for J-PARC experiments

J-PARC experiment with SKSExperiment Physics Reaction Beam Scat. SKS Comment

E05 Hyp (K-, K+) 1.8 1.1-1.4 SksPlusGood

momentum resolution

E13 ray (K-, -)1.5

(1.1-1.8)1.4 SksMinus

Large

Acceptance

E10 DCX (-, K+) 1.2 0.8-0.9SKS

(SksZero)

With

- reaction

E22Weak

(Single (+, K+) 1.05 0.63-0.73

SKS

(SksZero)Present

SKS spec

E19 search (-, K-) 1.92(1.87,1.97)

0.7-0.95SKS

(SksZero)Flat

acceptance

SksJ ? (SksJ+, SksJ-, SksJ0)

Detector configuration

Detector elements

SKS magnet

SDC : Drift chamber

TOF : Timing counter

SAC, SMF, SP0,

Iron block

SksMinus

(SksJ-)

Base Additional

D magnet, AC, TOF2,

DC3, (WC)

AC, LC

SksPlus

(SksJ+)

SksZero

(SksJ0)

(+each He Bag)

SksMinus

SKS magnet

SDC : Drift chamber

TOF : Timing counter

⇒Same as Base

+SAC,SMF,SP0

Optimized for the (K-, -) @ pK=1.5 GeV/c

Beam angle ~40°

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.

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.

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.

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

Acceptance

Magnetic field selection

Region cut• To select events which

path through inside of the region shown in right figure

• z-direction ±220 mm (magnet gap ±250 mm)

X

Y

Z

Acceptance is estimated taking into account the lack of the measured magnetic filed map.

SKS Acceptance

The simulated result is almost consist with the previous result.

~105 msr (100 msr). Absolute values is little la

rger than previous result.

⇒Size of SDCIn The acceptance of lower

momentum is smaller.

⇒AC position

2.2 T Map

SksMinus acceptance

Requirements (K-, -) 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.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)

(K-, -)

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.

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

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.

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

sct.<10°

SksZero acceptance

Requirements (-, K+) reaction @ 1.2 GeV/c

⇒ 0.8-0.9 GeV/c scattered particles p(-, K+)- reaction @ 1.2 GeV/c

⇒ 0.6-0.7 GeV/c scattered particles (+, K+) reaction @ 1.05 GeV/c

⇒ 0.63-0.73 GeV/c scattered particles p(-, K-)+ reaction @ 1.87, 1.92,

1.97 GeV/c ⇒ 0.7-0.95 GeV/c scattered particles

Comments DCX, (+, K+) 2.2 T⇒ search 2.4 T ⇒

DCX

(+, K+)

○ : 2.2 T Map

× : 2.4 T Map (2.7 T map scaled)

□ : 2.7 T Map

SksZero acceptanceRequirements (-, K+) reaction @ 1.2 GeV/c

⇒ 0.8-0.9 GeV/c scattered particles p(-, K+)- reaction @ 1.2 GeV/c

⇒ 0.6-0.7 GeV/c scattered particles (+, K+) reaction @ 1.05 GeV/c

⇒ 0.63-0.73 GeV/c scattered particles p(-, K-)+ reaction @ 1.87, 1.92,

1.97 GeV/c ⇒ 0.7-0.95 GeV/c scattered particles

Comments DCX, (+, K+) 2.2 T⇒ search 2.4 T ⇒

○ : 2.2 T Map

× : 2.4 T Map (2.7 T map scaled)

□ : 2.7 T Map

sct.<15°

DCX

(+, K+)

Momentum resolution

Simulation condition

Simulation condition Region cut

DC resolution (rms)SksMinus : In&Out 400 mSksPlus : In 300 m, Out 400 mSksZero : In 300 m, Out 400 m

Multiple scattering ⇒DC:Ar gas, He bag, other:Air He bag⇒SKS inside, between SDC3 and SDC4, between SKS and SDC3

In

Out

Drift chamber

He bag

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

2.2 T Map

0.70 MeV/c(FWHM)

@ 0.72 GeV/c

SksMinus momentum resolution

2.7 T Map

2.3 MeV/c(FWHM)

@ 1.4 GeV/c

The momentum resolution is little worse.

2.3 MeV/c(FWHM) @ 1.4 GeV/c

⇒ 2.1 MeV/c(FWHM) for previous simulations

SksPlus momentum resolution

2.7 T Map

1.8 MeV/c(FWHM)

@ 1.35 GeV/c

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.

○ : Previous SksPlus

× : SksPlus

SksZero momentum resolution

0.9 MeV/c(FWHM)

@ 0.69 GeV/c

2.2 T Map

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.

○ : Previous SKS

× : SksZero

DCX

(+, K+)

SksZero momentum resolution

○ : SksZero 2.2 T Map

× : SksZero 2.4 T Map (2.7 T Map scaled)

□ : SksZero 2.7 T Map

DCX

(+, K+)

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.

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 (+, K+) and search experiment.

• It is possible to construct the spectrometer system “SksJ ?” by using the same detector elements.

Problem (for SksZero)

• Beam through– The beam directly hits the down stream

detectors by using the (+, K+) reaction.

• Trigger rate and background events– Acceptance is increased Accepted ⇒

background events are increased.– For DCX and search experiment, the beam

hits the SKS magnet and makes the large background.

Beam through The beam hits the down stream

detectors by the (+, K+) reaction at p=1.05 GeV/c

The setup of SksZero is not optimized to avoid the beam through.

1.05 GeV/c