1. Future Plan of the Neutral Kaon Spectrometer 2 (NKS2) Experiment
Masashi Kaneta
Department of Physics
Tohoku University

2. Upgrade Project Physics motivation Detector upgrade
K+Y coincidence measurement
Advantage
No Fermi motion correction
Reaction Plane will be defined
Direct comparison with Model
Lambda polarization
Detector upgrade
Replacing inner detector
Replace straw drift chamber by a 3D tracker
increase the acceptance
Two-side-read-out hodoscope
increase dE/dx and TOF resolution
better particle separation
Masashi Kaneta, Tohoku Univ.

3. NKS2 detectors 110 mm 630 mm EV OH CDC IH SDC 400 mm
Two Drift Chambers
Cylindrical Drift Chamber (CDC) and Straw Drift Chamber (SDC)
Two Hodoscope
Inner and Outer Hodoscope (IH and OH)
Electron Veto
110 mm
New inner detectors should be fit in
630H x f tube
630 mm EV OH
CDC IH
SDC
400 mm
Masashi Kaneta, Tohoku Univ.

4. Design

5. Current/Future Inner Detectors Position
Liquid Deuterium target holder region
766 OH
712
286
232
42.6º
380
VDC 65 IH
134
300
SDC
100 78 IH
160
CDC
17.3º
748
530
630 55
200
210
1200
800
Masashi Kaneta, Tohoku Univ.

6. Vertex Drift Chamber Design
Requirements
As possible as small cell
but limited by feedthrough (f3mm)
At least 6 layers with stereo wires
Decision
Trapezoid (almost square) cell shape
Half cell size: 4 mm
8 layers
uu’ vv’ uu’ vv’
increasing stereo angle with radius: °
Drift gas = Ar:Ethane(50:50)
uu’
vv’
65 mm
55 mm
137 mm
Masashi Kaneta, Tohoku Univ.

7. Frame Safety factor min: 6.2 Concept CFRP pillar End-cap f160 mm
Less material
but to be strong
~216 kg total wire tension
CFRP pillar
20Lx40Wx0.5TH mm3
1.0TH = X0
target chamber: X0
IH: X0
End-cap f160 mm
426 mm height of pillar
390 mm wire height
This design has the most large safety factor in plans
min: 6.2
Masashi Kaneta, Tohoku Univ.

8. Readout FEE TDC bottom view side view ASD Align on VDC
Sony ASD chip
GNA-220
Align on VDC
like windmill
TDC
VME multi-hit TDC
Atlas muon TDC chip
Amsk co.
same with CDC
43.7
43.7
21.9
100
94.5
63.6
16.3
30°
side view
Masashi Kaneta, Tohoku Univ.

9. Acceptance

10. Acceptance for K 0S or L The acceptance with new chamber
Generated distribution: SLA model
K 0S (p+ p- channel)
L (p p- channel)
(1): all events
(2): the two daughters pass
through VDC with two OH his
(3): two daughters pass through OH
Note: Decay volume cut is applied for (2) and (3)
and lost ~80% of events
The acceptance with new chamber
~3 times for K0S
~1.5 times for 
Note: these values vary about 10%, depend on models used for input
Masashi Kaneta, Tohoku Univ.

11. Acceptance for K 0S + L Events
K 0S (p+ p- channel)
L (p p- channel)
(1): all events
(2): the four daughters pass
through VDC with two OH Hits
(3): four daughters pass through OH
Note: No decay volume cut is applied
The acceptance will increase
~8 times
Masashi Kaneta, Tohoku Univ.

12. Polarization Measurement
Transverse polarization
measurement pL
t = pg×pL
reaction plane
in CM
polarization
Acceptance
decay parameter
0.642 (PDG) pN qK pg
Acceptance correction
May vary with
Cos(qKcm), Eg
 momentum
Polarization
Test results
No Polarization dependences
PL is smeared by resolution
factor ~0.9 pK t
LCM q pp
Masashi Kaneta, Tohoku Univ.

13. Model Predictions: Self L Polarization
g+p  K ++L
g+n  K 0+L
(rKK=-2.087)
SLA
KaonMAID
L Polarization
(P. Bydzolvski)
SA1
q of Kaon in CM [degree]
Masashi Kaneta, Tohoku Univ.

14. Schedule

15. Schedule
March
April
May
June
July
construction
VDC
check at
test bench
Installation
in NKS2
Test Exp.
w/ Beam IH
design
construction
The test experiment of new detectors will be before summer shutdown
Masashi Kaneta, Tohoku Univ.

16. Summary The detector upgrade project is on going New inner detectors
Goal: K+Y coincidence measurement
Increasing acceptance of tracking
Increasing start time resolution of TOF
better /K/p separation toward K++Y measurement
New inner detectors
Expecting ~8 times K0S+L events
Schedule
Test experiment before summer
Beam time will be requested
Masashi Kaneta, Tohoku Univ.

17. Materials CFRP Scintillator Target cell C:H:O = 75:5:20
density = 1.55 g/cm3
radiation length = cm
1 mm thickness = X0
Scintillator
C:H = 8:8 atoms
density = g/cm3
radiation length = cm
5 mm thickness = X0
Target cell
0.009X0
Masashi Kaneta, Tohoku Univ.

18. Masashi Kaneta, Tohoku Univ.