J-PARC E06 K + →π 0 μ + ν(Kμ3) を用いた 時間反転非保存探索実験における 新型光センサーの活用法 Dec 8, 2006 第 2 回次世代光センサーに 関するワークショップ 清水俊 大阪大学理学研究科

Transverse muon polarization Spurious effects from final state interaction are small. Non- zero P T is a signature of T violation. Clear channel to search for T violation. Long history of theoretical and experimental studies. (J.J. Sakurai, 1957) Experiment at KEK(E246) P T =  ± (stat) ± (syst) ( |P T | < : 90% C.L. ) PRD73, 72005(2006) K + →     decay T-odd

Matrix element of K + →     decay P T is sensitive to scalar couplings. T-violation parameter : Im(ξ) Im(ξ)≠0 T-violation

Theoretical aspects Standard Model contribution to P T : –Only from vertex radiative corrections and P T (SM) < Spurious effects from final state interactions (FSI): P T (FSI) < There is a large window for new physics beyond the SM in the region of P T = ~ There are theoretical models which allow sizeable P T without conflicting with other experimental constraints. Multi-Higgs doublet (3 Higgs doublet) model (MH) SUSY with s-quark mixing (SUS) SUSY with R-parity violation (SUR)

KEK 全体図 KEK-12GeV PS

Stopped K + method Large solid angle and high resolution of Toroidal Spectrometer and CsI(Tl) calorimeter side view end view decay T-violation search in KEK E246 experiment

Experimental setup

Double ratio measurement ＋ P T (π 0 forward) ＝ － P T (π 0 backward) P N contribution to systematic error is drastically reduced. Determination of P T Stopped K + beam Stopped K + のため target と、 fwd/bwd π 0 検出器 が重要な鍵となる。

K + 静止用ターゲッ ト K + 静止崩壊用ターゲット 直径 8cm のプラスティック ２５ 6 本のシンチレーションファイバー で構成 読み出し： PMT （浜松 H1635) K + 崩壊位置を特定する

Pπ 測定 measurement of P π, P μ,S μ P π ： CsI(Tl) calorimeter Using Stopped K + not only 2 γ but also 1 γ with high energy σ ＝１４ MeV

CsI(Tl) photon detector Segmentation  =  = 7.5 o Number of crystals 768 Length of crystals 25 cm (13.5 X 0 ) Inner radius 20 cm Outer radius 50 cm Solid angle ~75%of 4  Readout PIN diode Light yield p.e./MeV Equiv. noise level 65 keV ΔE/E 12-14% at 1257 keV( 22 Na) σ E 3% at 200MeV D.V.Dementyev et al. Nucl. Instr. Method A440 (2000) 151 Pin diode 使用により、 強磁場での利用可能 省スペース化

E246 result P T =  ± (stat) ± (syst) ( |P T | < : 90% C.L. ) Im  =  ± (stat) ± (syst) ( |Im  | <0.016 : 90% C.L. ) Statistical error dominant A T = (A fwd  A bwd ) / 2 N cw  N ccw A fwd(bwd) = N cw  N ccw P T = A T / {  }  : analyzing power : attenuation factor Im  = P T / KF KF : kinematic factor

New experiment at J-PARC We aim at a sensitivity of  P T ~10 -4 (E246-  P T ~10 -3 )  Statistical error  P T stat ≤ 0.1  P T stat (E246) ~10 -4 with 1) × 30 of beam intensity, 2) × 10 of detector acceptance, and 3)higher analyzing power Systematic error  P T syst ~ 0.1  P T syst (E246) ~10 -4 by 1) precise calibration of misalignments using data 2) correction of systematic effects JPARC

J-PARC 施設 Parameters of Main Ring Extraction Beam Energy 50 GeV Average Beam Current 15 μA Repetition 0.3 Hz Extraction Scheme Fast, and Slow

Method of experiment Stopped K + decay –Superior to in-flight decay Toroidal spectrometer E246 detector upgrade –Well known performance –Well studied systematics –Good alignment in magnet and CsI(Tl) –Lower cost FoM (A√N) distribution Detector acceptance

Upgrade of the detector Muon polarimeter passive → active Muon magnetic field toroid → muon field magnet Target smaller and finer segmentation Charged particle tracking addition of two chambers CsI(Tl) readout PIN diode → APD New analysis scheme

Target Smaller size (smaller beam spot) Finer segmentation Sci. fiber of 20 cm length Clear fiber or direct attachment Light readout by SiPMTs Diameter 6 cm Active length 20 cm Fiber size 2.5 × 2.5 mm No. of fibers 432 Light readout 4 clear fibers Light yield ~ 10/SiPMT

Target and tracking Better kinematical resolution Stronger K  2 dif  + BG suppression Addition of C0 and C1 GEM chambers with - high position resolution - higher rate performance Larger C3-C4 distance Use of He bags New target E246J-PARC

CsI(Tl) readout CsI(Tl) + APD + Amplifier + FADC Electrons after APD : ~ 2 × MeV Max count rate / module : ~ 100 kHz Max K + decay rate : ~ 20 MHz - enough for the beam intensity in Phase 1 Noise level : to be tested Module energy resolution : to be tested -Energy resolution is determined by lateral shower leakage

Sensitivity estimate Source  P T Net run time 1.0 ×10 7 s Proton beam intensity 9  A on T1 K + beam intensity 3×10 6 /s Total number of good K  3 2.4×10 9 Total number of fwd/bwd (N) 7.2×10 8 Sensitivity coefficient 3.73√N Total ~ Statistical sensitivitySystematic errors Source  P T  z <  z <  e +, E e + < Total ~ JPARC

Summary P T in K  3 is a very sensitive probe of new physics We propose a J-PARC experiment in the early stage of Phase 1 to pursue a limit of  P T ~ K0.8 beamline as a branch of K1.1 Upgraded E246 detector Beam time request = 1.3×10 7 s (net) at I p = 9  A on T1 We would like to take the first step this year toward –Collaboration forming –Fund application –Detector R&D after obtaining some status.