1. 1 Progress Report to PAC3 J-PARC E06 Experiment (TREK) Measurement of T-violating Transverse Muon Polarization (P T ) in K + →     Decays J. Imazato July 6, 2007

2. 2 Problem assigned by PAC1 The PAC would like the proponent to show that the improvement on the sensitivity and systematic uncertainty below 10 -4 is attainable via detailed Monte Carlo studies, e.g. acceptance, B-field offset, detector misalignments and the new polarimeter.

3. 3 Outline Statistical sensitivity estimate Systematic error estimate Polarimeter misalignments Other systematics R&D for the detector upgrade Collaboration/Cost/Funding/Beam Summary

4. 4 Transverse polarization in K  3 K + →     decay P T is T-odd and spurious effects from final state interaction are small. Non-zero P T is a signature of T violation. Standard Model contribution to P T : P T (SM) < 10 -7 Spurious effects from final state interactions : P T (FSI) < 10 -5 There are theoretical models which allow sizeable P T without conflicting with other experimental constraints.

5. 5 P T measurement N cw - N ccw A fwd(bwd) = ; A T = (A fwd - A bwd ) / 2 N cw - N ccw Use of upgraded E246 detector P T measured as the azimuthal asymmetry of the  + decay e +

6. 6 Statistical sensitivity estimate

7. 7 Factors for statistical sensitivity K + beam intensity × Run time K + stopping efficiency (  stop ~ 0.30 according to a MC ) K + →      event rate with  + in the polarimeter ❶ –E246 experience + MC calculation    →e +  event rate with e + detected, and polarization analyzing power :  = A T / P T ❷ –MC calculation for the new active polarimeter In determining the sensitivity, ❶ and ❷ are separable. They are shown next step by step. _

8. 8 Positron asymmetry measurement E06: conservative estimate now by fwd/bwd ambitious analysis including left/right event-by-event analysis: future option E246:  0 - forward (fwd) and backward (bwd) integral analysis

9. 9 Optimum e + measurement E e th = 38 MeV cos  e th = 0.34  = 0.38 (cf. 0.27 in E246) P T = A T /   : analyzing power, : attenuation factor Figure of Merit (FoM) optimization by a MC simulation using a realistic  + stopper condition FoM = A T √N e +

10. 10 Optimum  0 measurement cos   th = 0.30 = 0.68 P T = A T / 0.258 Optimization of   th by FoM of FoM = √N  o cos  T ≈ cos   0 up to finite  + acceptance   +

11. 11 K  3 event rate and sensitivity Standard event selection conditions as in E246 : 1.65 < M  < 185 MeV/c 2 2.3500 < M 2 TOF < 18,000 (MeV/c 2 ) 2 3. p   <185 MeV/c 4.  + incident into the polarimeter 5.      < 160 o 6.M 2 missing > -15,000 (MeV/c 2 ) 2 ⇒ Detector acceptance    = 1.14 ×10 -2 N(K  ) = N(K + ) ・  stop ・ Br(K  ) ・    = 3.3 × 10 9 (total E06 good events) MC calculation for 10 8 events and using P T =A T / 0.258 :  P T = 6.9 / √N(K  ) = 1.2 ×10 -4

12. 12 Left-right  0 analysis MC study :  P T = 1.6 × 10 -4  P T = 1.0 × 10 -4 (combined) How about systematics?  Careful MC studies needed.   PLPL PLPL ~ A z (  0 ) =  cos(  t +  )

13. 13 Summary of statistical sensitivity  P T =1.2 × 10 -4 for the fwd+bwd integral analysis compared with  P T = 1.8 × 10 -4 given in the proposal. –Significant gain due to  e cut and realistic event selection (The effect of E e + threshold was partially included in the proposal.) We will attack the event-by-event weighted analysis aiming for  P T = 1.0 × 10 -4 (fwd+bwd) and  P T = 0.8 × 10 -4 (including left+right).

14. 14 Update of run time K + beam intensity @ 9  A p on T1 is now 2.1 × 10 6 /s Necessary run time is now 1.4 × 10 7 s. ( It was 1.0×10 7 s in the proposal.) K1.1-BR beam optics was changed due to B1 position 2005 design 2007 design Acc = 6.0 msr %  p/p Acc = 4.5 msr %  p/p

15. 15 Systematic error estimate

16. 16 Source of Error  12 fwd/bwd  P T x 10 4 e + counter r-rotationxo0.5 e + counter z-rotationxo0.2 e + counter f-offsetxo2.8 e + counter r-offsetoo<0.1 e + counter z-offsetoo<0.1  + counter f-offsetxo<0.1 MWPC  -offset (C4)xo2.0 CsI misalignmentoo1.6 B offset (  )xo3.0 B rotation (  x )xo0.4 B rotation (  z )xx5.3 K + stopping distributionoo<3.0  + multiple scatteringxx 7.1 Decay plane rotation (  r )xo1.2 Decay plane rotation (  z )xx0.7 K  2 DIF backgroundxo0.6 K + DIF backgroundox< 1.9 Analysis--3.8 Total11.4 E246 systematic errors Cancellation by  12 and/or fwd/bwd almost all systematics except for :  + field alignment  + multiple scattering decay plane shifts due to K + stopping distribution Detector inefficiency distribution etc.

17. 17 Suppression of systematic errors in E06  + field alignment :   P T < 10 -4 –P T analysis free from misalignment  + multiple scattering :  P T < 0 –no longer relevant with the active polarimeter decay plane shifts :  P T < 10 -4 –correction for P T only with statistical uncertainty active polarimeter e + analysis :  P T < 10 -4 – Perfect fwd/bwd cancellation mechanism Old errors Newcomer  P T syst ~ 0.1  P T syst (E246) ~10 -4

18. 18 e + asymmetry due to polarimeter misalignment Rotation about Component r-axis z-axis Polarimeter  r  z Muon field  r  z fwd - bwd : vanishes for  r,  z,  r when t-integrated fwd - bwd : not vanishing for  z ! spurious A T ?

19. 19 Misalignment analysis using K  3  z ~  r ~ 3 × 10 - 4 for misalignment determination  P T < 1.2 × 10 - 4 for P T determination from A sub A sum (  0 ) A sub (  0 ) Asymmetry analysis in terms of  0 : in plane spin angle from z-axis PTPT+zPT+rPT+z+rPTPT+zPT+rPT+z+r

20. 20 Alignment calibration with K  2 Use of pure P L component with  0 dependence A(   )=   {  r cos  0 -  z sin  0 +  (  0 )} (  ≪  r,  z ) Special run with B=1.35 T ( > 0.9 T of K  3 main run) Use of pure P r component of K  2 decay-in-flight muons is also possible Cross-checking the K  3 measurement  0 accuracy  z sin  0  r cos  0 x10 2

21. 21 Systematic error (1) associated with misalignment analysis P T can be deduced regardless of the existence of the polarimeter misalignments,  r,  z,  r and  z. But, how much is the systematic error induced in this misalignment analysis? Simulation calculation with: P T = 0 and  z =  r = 5 o = 87 mr ==>  P T = (2±7) × 10 -4 for 10 8 events Essentially statistical error of P T No significant effect beyond the statistical error In reality,  z ~  r ~ 1 mr :   P T syst should be < 10 -4

22. 22 Systematic error (2) due to K  2 BG Dangerous  + ->    background with a P T component Substantial reduction due to the addition of the C0 chamber Cancellation in gap integration ==> averaging to < 1/10 (<0.02%)  0 - fwd/bwd cancellation ==> suppression to < 1/10 (<0.002%)  P T < 10 -4 MC simulation Momentum resolutionsConsistency

23. 23 Systematic error (3) associated with decay plane rotation correction Two rotation angles of  z and  r Relation:  P T ~ 0.5 due to P N and P L admixture is fwd/bwd cancelling, but is not fwd/bwd cancelling. P T will be corrected for and Statistical error of the correction  =  (  z ) /√N total  P T ( ) ≪  P T stat ~ 10 -4   z distribution in E246 = -0.004±0.12 mr -1 0 +1 0  P T ( ) ≪ 10 -4  P T ( ) ~  P T stat & fwd/bwd ≪ 10 -4

24. 24 Systematic errors (4) associated with positron analysis Systematics in the chamber measurement is left-right canceling : cell inefficiency plate non-uniform thickness etc. further cancellation by fwd-bwd up to small  =  fwd -  bwd  symmetrization of  with bias   fwd (r,y,z) =  bwd (r,y,z)  P T fwd = P T +  P T ’  P T bwd = -P T +  P T ” No problem Cancellation power will be calculated using data.  =  fwd -  bwd was a few % in E246  P T should be < 10 -4  + stopping distribution in the stopper

25. 25 Summary of systematic errors  P T syst ≦ 10 -4 for the sources now conceivable.

26. 26 R&D of detector upgrade

27. 27 Upgraded elements

28. 28 Summary of R&D in this past year We confirmed basic performances of the upgraded elements ElementR&D itemGroup/PlaceResultsConclusion PolarimeterStopper μSRCanada,Japan /TRIUMF Relaxation rate (λ TF, λ LF ) Al,Mg alloys CsI(Tl)APD readoutINR/INRC.R. electron yield E-width, t- resol. APD readout is O.K. TargetMPPC readout INR,KEK /INR,KEK p.e. yield2.5×2.5 mm 2 O.K. MPPC readout O.K. Target- MPPC Rad. hardnessJapan/RCNPLeakage currentbeing investigated C0 and C1GEM chamber MIT/FNALStable operation x-resol., rate cap. C0, C1 (GEM) μ + magnet3D calculation Japan/KEKField direction etc. No problem in design

29. 29 Stopper  SR study (Canada, Japan) TRIUMF surface muon beam with full polarization E1120 experiment to study  SR in Al and Mg alloys Transverse field (TF) and longitudinal field (LF) relaxation rates were measured with a 0.03 T field. Several candidate stopper materials were confirmed. Al alloys: A5052, A6063, Mg alloys: AZ31, ZK60, Z6, AM60, AZ91 Muon spin behavior was studied for candidate stopper materials Typical TF precession pattern

30. 30 CsI(Tl) readout (INR) Cosmic ray test Energy Timing First application of APD readout to a large CsI(Tl) calorimeter Very good timing characteristics were confirmed  t =3ns

31. 31 Fiber target (INR, KEK) 2.5x2.5 mm x 20 cm fiber Tapered coupling to MPPC Yield of ~ 20 p.e. for 90 Sr Target cross section Light yield test of the fiber 20 cm + clear fiber + MPPC Pulse height spectrum Pulse shape MPPC radiation hardness test at RCNP Increasing leakage current with dose Design of shielding

32. 32 C0 and C1 GEM chambers (MIT) Three chambers were beam-tested at FNAL by MIT GEM Lab. H- and V-amplitude correlation Middle residual Stable operation Resolution of  x = 90  m Rate capability Readout electronics Amplitude vertical Amplitude horizontal Residual x (mm)

33. 33 Muon field magnet (KEK) TOSCA 3D calculation

34. 34 Collaboration/Funding/Beamline

35. 35 Collaboration Canada Univ. of Saskatchewan, Univ. of British Columbia, TRIUMF, Univ. of Montreal U.S.A. MIT, Iowa State Univ., Univ. of South Carolina Japan KEK, Osaka Univ., Tohoku Univ., Kyoto Univ., NDA - New participation - Russia INR (group with E246 experience) Altogether Vietnam Nat. Sci. Univ. in HCMC 35 people International cooperation in detector construction Strong support from : (1) TRIUMF detector shop, and (2) MIT GEM Lab.

36. 36 Beamline preparation K1.1 K1.1-BR K1.1BR uses the upstream part of K1.1. No budget is allocated for K1.1 in the J-PARC budget, although it is one of the planned secondary lines in Phase 1. We would like to go ahead with the BR (700-800 MYen), with a possible Canadian contribution to the 0.8 GeV leg. Once full beam operation has started at T1, it will become very difficult to install the frond end of the channel (B1, Q1, Q2, B2). Timely installation of K1.1/K1.1BR is absolutely necessary. T1

37. 37 Cost estimate and funding policy Updated cost estimate : –Detector upgrade etc. 279,710 kYen –Transfer of the SC spectrrometer 182,000 kYen –K1.1BR branch construction 50,000 kYen (These are not very different from the estimates in the proposal.) Policy for funding :

38. 38 Time schedule Totally dependent on the K1.1-BR beamline installation and funding of the experiment. In the proposal we presented: 2009 1) Spectrometer setup 2) Field mapping 3) Detector setup 4) Beam tuning 2010-11 5) Engineering run, and 6) Data taking We would like to pursue the earliest possible schedule aiming to provide the first particle physics output from the hadron hall.

39. 39 Theory impact A clean search for CP violation via Higgs dynamics. Direct CP violation presumably unsuppressed by  I=1/2 rule P T ~ [  ’  effect  × 20 = 5 x 10 -6 × 20 ~ 10 -4 -- unless enhanced couplings to leptons! ( I. Bigi, CERN Flavor WS, 2007 )

40. 40 Summary We have shown with MC studies that E06 can reach at least the statistical sensitivity of  P T =1.2×10 -4 in the safe fwd+bwd integral analysis. We have established a P T extraction method in the presence of any polarimeter misalignments. We have shown that other systematics should be controllable to the level < 10 -4. We have demonstrated the validity of the proposed upgraded detector elements with necessary test experiments.

41. PAC3 41 Our request to PAC The Canadian and American groups are starting budget requests in their countries. The status of stage-2 approval is very necessary for a successful application. The PAC is requested to consider E06 for the stage-2 approval although there are no funds yet in place. An endorsement of the K1.1BR beamline installation for E06 is desirable. The PAC is also asked to make a strong recommendation to the IPNS/J-PARC management to provide a plan for the K1.1BR construction so that the Canadian group will be able to request money for a contribution to this stopped K + beamline.

42. 42 END of Slides

43. 43 K + Stopping efficiency Optimum degrader thickness Target diameter of d=8cm d=6cm d=4cm FOM is maximum at 800 MeV/c  stop =0.25~0.30 GEANT3 calculation

44. 44 Stopped beam method P T = - 0.0017 ± 0.0023(stat) ± 0.0011(syst) ( |P T | < 0.0050 : 90% C.L. ) Im  = - 0.0053 ± 0.0071(stat) ± 0.0036(syst) ( |Im  | <0.016 : 90% C.L. ) Statistical error dominant Double ratio experiment 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 bwd -    fwd -   

45. 45 Target of E06 E246 detector is upgraded for E06

46. 46 Sensitivity improvement in E06 We aim at a sensitivity of  P T ~10 -4  P T stat ~0.05  P T stat (E246) ~10 -4 with 1) × 30 beam intensity, 2) × 10 detector acceptance, and 3)Higher analyzing power  P T syst ~ 0.1  P T syst (E246) ~10 -4 by 1) Precise calibration of misalignments using data 2) Correction of systematic effects 3)Precise fwd-bwd cancellation of systematics by data symmetrization (Estimate of cancellation power using data) Most crucial systematics are misalignment of : Muon polarimeter and muon field distribution

47. 47 E246 muon polarimeter Cross sectionOne-sector view y(cm) B   + → e + e  W(e+ ) ∝ 1 + A cos  Passive polarimeter with Al muon stopper Left/Right positron counters simple analysis and systematics

48. 48 Active muon stopoper Identification of muon stopping point/ decay vertex Measurement of positron energy E e + and angle  e + Large positron acceptance of nearly 4  Larger analyzing power Higher sensitivity Lower BG in positron spectra Parallel plate stopper with Gap wire chambers Number of plates 31 Plate material Al, Mg or alloy Plate thickness ~ 2 mm Plate gap ~ 8 mm Ave. density 0.24  Al   stop efficiency ~ 85% Small systematics for L/R e + asymmetry measurement Fit for  0 fwd/bwd measurement Simple structure

49. 49 Spin relaxation rate

50. 50 Tracking system E246 J-PARC E06 C0 (cylindrical) and C1(planer) are GEM chambers

51. 51 Tracking performance

52. 52 Rad.hardness test of MPPC MPPC 400 pixel type Irradiation of up to 36 Gy Increase of leakage current proportional to dose

53. 53 Beam halo simulation GEANT4 simulation 10 cm-  BeO degrader + 6 cm-  Target K + flux distribution  +  + e + n

54. 54 CsI(Tl) readout CsI(Tl) + APD + Amplifier + FADC Electrons after APD : ~ 2 ×10 7 @ 100 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

55. 55 APD readout of CsI(Tl) E246 CsI(Tl) 5 x 5mm APD CR measurement 1.5  s width

56. 56 Tracking system alignment Use of a collimator system

57. 57 CsI(Tl) alignment Use of K + →     with back to back kinematics azimuthal rotation two tilt angles

58. 58 e + asymmetry due to polarimter misalignmnet

59. 59 Precession patterns due to misalignments  r =1 o  r =1 o  z =1 o  z =1 o @  = 0 o - A kind of normalization -

60. 60 Misalignment analysis Effects of  z and  r vanish.  0 determination event-by-event using K  3 form factors. Ambiguity of  0 determination is not problematic. Time-integrated asymmetry function

61. 61   dependence of the asymmetry  0 -fwd  0 -bwd PTPT  z =5 o  r =5 o N

62. 62 Correction for decay plane rotation Two rotation angles of  z and  r Relation:  P T ~ 0.5, ~ 0.5 P T will be corrected for and is fwd/bwd cancelling, but Statistical error of the correction  =  (  z )/√N total  P T ( ) ≪  P T stat ~ 10 -4  z distribution in E246 = -0.004±0.12 mr -1 0 +1 0 is not fwd/bwd cancelling.

63. 63 Data symmetrization K + stopping distribution non-bias cut small loss of events - Suppression of systematic errors -  + stopping distributions   fwd (r,y,z) ≠  bwd (r,y,z) ⇩  fwd (r,y,z) =  bwd (r,y,z)  P T fwd = P T +  P T ’  P T bwd = -P T +  P T ”  eliminates systematics  in the polarimeter

64. 64 Group members : core members (younger people)

65. 65 Trigger rate reduction