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Progress Report: T-Violation Measurement Study in K+→p0m+n Decays

This report outlines the progress in analyzing T-violating transverse muon polarization in K+→p0m+n decays through Monte Carlo studies and systematic error estimates. Detailed information on the factors influencing statistical sensitivity and systematic errors is provided, along with the optimization process for the measurement parameters. The report also discusses the effective suppression of systematic errors in the experiment.

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Progress Report: T-Violation Measurement Study in K+→p0m+n Decays

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  1. Progress Report to PAC3J-PARC E06 Experiment (TREK)Measurement of T-violating Transverse Muon Polarization (PT) in K+→p0m+n DecaysJ. ImazatoJuly 6, 2007

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

  4. Transverse polarization in Km3 K+→p0m+ndecay • PT is T-odd and spurious effects from final state interaction are small.Non-zero PTis a signature of T violation. • Standard Model contribution to PT: PT(SM) < 10-7 • Spurious effects from final state interactions : PT(FSI) < 10-5 • There are theoretical models which allow sizeable PT • without conflicting with other experimental constraints.

  5. PT measurement Use of upgraded E246 detector PT measured as the azimuthal asymmetry of the m+ decay e+ Ncw - Nccw Afwd(bwd) = ; AT = (Afwd - Abwd) / 2 Ncw - Nccw

  6. Statistical sensitivity estimate

  7. Factors for statistical sensitivity _ • K+ beam intensity × Run time • K+ stopping efficiency (estop~0.30according to a MC ) • K+→p0m+n event rate with m+ in the polarimeter ❶ • E246 experience + MC calculation • m+→e+nn event rate with e+ detected, and polarization analyzing power : a = AT / PT❷ • MC calculation for the new active polarimeter In determining the sensitivity,❶and❷are separable. They are shown next step by step.

  8. Positron asymmetry measurement • E246: • p0- forward (fwd) • and backward (bwd) • integral analysis • E06: • conservative estimate now by fwd/bwd • ambitious analysis including left/right • event-by-event analysis: future option

  9. Optimume+measurement • PT = AT / a <cosqT> • a : analyzing power, • <cosqT> : attenuation factor • Figure of Merit (FoM) optimization by a MC simulation using a realistic m+ stopper condition FoM = AT√Ne+ • Eeth = 38 MeV • cosqeth = 0.34 • a = 0.38 (cf. 0.27 in E246)

  10. Optimum p0 measurement • cosqT ≈ cosqp0 • up to finite m+ acceptance qm+ • cosqpth = 0.30 • <cosqp0> = 0.68 • PT = AT/ 0.258 • Optimization of qpth by FoM of • FoM = <cosqp0> √Npo

  11. Km3 event rate and sensitivity • Standard event selection conditions as in E246 : • 65 < Mgg < 185 MeV/c2 • 3500 < M2TOF < 18,000 (MeV/c2)2 • pm+ <185 MeV/c • m+ incident into the polarimeter • qm+p0 < 160o • M2missing > -15,000 (MeV/c2)2 ⇒ Detector acceptanceW(Km3) = 1.14 ×10-2 N(Km3) = N(K+)・estop・Br(Km3)・ W(Km3) = 3.3 × 109 (total E06 good events) • MC calculation for 108 events and using PT =AT / 0.258 : dPT = 6.9 / √N(Km3) = 1.2 ×10-4

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

  13. Update of run time • K1.1-BR beam optics was changed due to B1 position 2005 design 2007 design • K+ beam intensity @ 9mA p on T1 is now 2.1×106 /s • Necessary run time is now 1.4×107 s. ( It was 1.0×107 s in the proposal.) Acc = 6.0 msr %Dp/p Acc = 4.5 msr %Dp/p

  14. Systematic error estimate

  15. E246 systematic errors Source of ErrorS12 fwd/bwddPTx 104e+ counter r-rotation x o 0.5e+ counter z-rotation x o 0.2e+ counter f-offset x o 2.8e+ counter r-offset o o <0.1e+ counter z-offset o o <0.1m+ counter f-offset x o <0.1MWPC f-offset (C4) x o 2.0CsI misalignment o o 1.6B offset (e) x o 3.0B rotation (dx) x o 0.4B rotation (dz) x x5.3K+ stopping distribution o o <3.0m+ multiple scattering x x7.1Decay plane rotation (qr) x o 1.2Decay plane rotation (qz) x x0.7Kp2 DIF background x o 0.6K+ DIF background o x < 1.9Analysis - - 3.8Total 11.4 • Cancellation by S12 and/or fwd/bwdalmost all systematics • except for : • m+ field alignment • m+ multiple scattering • decay plane shifts • due to • K+ stopping distribution • Detector inefficiency • distribution etc.

  16. Suppression of systematic errors in E06 Old errors • m+ field alignment : dPT < 10-4 • PT analysis free from misalignment • m+ multiple scattering : dPT < 0 • no longer relevant with the active polarimeter • decay plane shifts : dPT < 10-4 • correction for PT only with statistical uncertainty • active polarimeter e+ analysis : dPT < 10-4 • Perfect fwd/bwd cancellation mechanism Newcomer • dPTsyst ~ 0.1 dPTsyst (E246) ~10-4

  17. e+ asymmetrydue topolarimeter misalignment Rotation about Component r-axis z-axis Polarimeter erez Muon field drdz fwd - bwd : vanishes for er , ez , dr when t-integrated fwd - bwd : not vanishing for dz ! spurious AT ?

  18. Misalignment analysis using Km3 Asymmetry analysis in terms of q0 : in plane spin angle from z-axis PT PT+dz PT+dr PT+dz+dr Asum(q0) Asub(q0) • Ddz ~ Ddr ~ 3×10-4 for misalignment determination • dPT < 1.2×10-4 for PT determination from Asub

  19. Systematic error (1) associated withmisalignment analysis • Simulation calculation with: PT= 0 and dz = dr= 5o = 87 mr ==> dPT= (2±7)×10-4 for 108 events • Essentially statistical error of PT • No significant effect beyond the statistical error • In reality, dz ~ dr ~ 1 mr : • dPTsystshould be < 10-4 • PT can be deduced regardless of the existence of the polarimeter misalignments, er, ez, dr and dz. • But, how much is the systematic error induced in this misalignment analysis?

  20. Systematic error (2) due to Kp2 BG Momentum resolutions Consistency MC simulation • Cancellation in gap integration • ==> averaging to < 1/10 (<0.02%) • p0 - fwd/bwd cancellation ==> suppression to < 1/10 (<0.002%) dPT < 10-4 • Dangerous p+ -> m+n background with a PT component • Substantial reduction due to the addition of the C0 chamber

  21. Systematic error (3) associated with decay plane rotation correction • Two rotation angles of qz and qr • Relation: dPT ~ 0.5 <q>due to PN and PL admixture • <qr> isfwd/bwd cancelling, but <qz> isnot fwd/bwd cancelling. • PTwill be corrected for <qz> and <qr> qz distribution in E246 <qz>= -0.004±0.12 mr • Statistical error of the correction • d<qz> = s(qz) /√Ntotal • dPT (<qz>) ≪dPTstat ~ 10-4 dPT (<qz>) ≪ 10-4 dPT (<qr>) ~dPTstat&fwd/bwd ≪ 10-4 -1 0 +1 0

  22. 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 Dr = rfwd - rbwd • symmetrization of r with bias • rfwd(r,y,z) = rbwd(r,y,z) • PTfwd = PT + dPT’ • PTbwd = -PT+ dPT” No problem • Cancellation power will be calculated using data. m+ stopping distribution in the stopper Dr = rfwd - rbwd was a few % in E246 dPTshould be < 10-4

  23. R&D of detector upgrade

  24. Upgraded elements

  25. Stopper mSR study (Canada, Japan) • Muon spin behavior was studied for candidate stopper materials Typical TF precession pattern • TRIUMF surface muon beam with full polarization • E1120 experiment to study mSR 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

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

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

  28. 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 • Dx = 90 mm • Rate capability • Readout electronics Amplitude vertical Amplitude horizontal Residualx(mm)

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

  30. Collaboration/Funding/Beamline

  31. Collaboration • International cooperation in detector construction • 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 • Strong support from : (1) TRIUMF detector shop, and • (2) MIT GEM Lab.

  32. Beamline preparation K1.1 • 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. K1.1-BR T1

  33. 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 :

  34. Time schedule • Totally dependent on the K1.1-BR beamline installation and funding of the experiment. • In the proposal we presented: 20091) 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.

  35. Theory impact • A clean search for CP violation via Higgs dynamics. • Direct CP violation presumably unsuppressed by DI=1/2 rule PT ~ [e’/e effect]× 20 = 5 x 10-6× 20 ~ 10-4 -- unless enhanced couplings to leptons! (I. Bigi, CERN Flavor WS, 2007 )

  36. Summary • We have shown with MC studies that E06 can reach at least the statistical sensitivity of dPT =1.2×10-4 in the safe fwd+bwd integral analysis. • We have established a PT 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.

  37. 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. PAC3

  38. END of Slides

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

  40. Stopped beam method • Double ratio experiment • AT = (Afwd - Abwd) / 2 • Ncw - Nccw • Afwd(bwd) = • Ncw - Nccw • PT = AT / {a <cosqT>} • a : analyzing power • <cosqT> : attenuation factor • Imx = PT / KF • KF :kinematic factor PT = - 0.0017 ± 0.0023(stat) ± 0.0011(syst) ( |PT | < 0.0050 : 90% C.L. ) Imx = - 0.0053 ± 0.0071(stat) ± 0.0036(syst) ( |Imx | <0.016 : 90% C.L. ) bwd -p0 (g ) fwd -p0 (g ) Statistical error dominant

  41. Target of E06 • E246 detector is upgraded for E06

  42. Sensitivity improvement in E06 • We aim at a sensitivity of dPT ~10-4 • dPTstat ~0.05 dPTstat (E246) ~10-4 with 1) ×30 beam intensity, 2) ×10 detector acceptance, and • Higher analyzing power dPTsyst ~ 0.1 dPTsyst (E246) ~10-4by 1) Precise calibration of misalignments using data 2) Correction of systematic effects • 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

  43. E246 muon polarimeter One-sector view Cross section B y(cm) _ m+ →e+ne nm W(e+) ∝ 1 + A cos q • Passive polarimeter with • Al muon stopper • Left/Right positron counters • simple analysis and systematics

  44. Active muon stopoper • Identification of muon stopping point/ decay vertex • Measurement of positron energy Ee+ and angle qe+ • Large positron acceptance of nearly 4p • 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 rAl m+ stop efficiency ~ 85% • Small systematics for L/Re+ asymmetry measurement • Fit for p0fwd/bwd measurement • Simple structure

  45. Spin relaxation rate

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

  47. Tracking performance

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

  49. Beam halo simulation • GEANT4 simulation • 10 cm-f BeO degrader + 6 cm-fTarget K+ flux distribution p+ m+ e+ n

  50. CsI(Tl) readout • CsI(Tl) + APD+ Amplifier + FADC • Electrons after APD : ~ 2 ×107 @ 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

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