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

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.

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 f110-400 tube 630 mm EV OH CDC IH SDC 400 mm Masashi Kaneta, Tohoku Univ.

Design

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.

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:6.0 - 11.1° Drift gas = Ar:Ethane(50:50) uu’ vv’ 65 mm 55 mm 137 mm Masashi Kaneta, Tohoku Univ.

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 = 0.004 X0 target chamber: 0.009 X0 IH: 0.012 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.

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.

Acceptance

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.

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.

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.

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.

Schedule

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.

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.

Materials CFRP Scintillator Target cell C:H:O = 75:5:20 density = 1.55 g/cm3 radiation length = 26.66 cm 1 mm thickness = 0.0038 X0 Scintillator C:H = 8:8 atoms density = 1.032 g/cm3 radiation length = 42.43 cm 5 mm thickness = 0.0118 X0 Target cell 0.009X0 Masashi Kaneta, Tohoku Univ.

Masashi Kaneta, Tohoku Univ.