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Measurement of T-violating Transverse Muon Polarization in K + → p 0 m + n Decays at J-PARC

Oct. 6, 2006 SPIN2006. Measurement of T-violating Transverse Muon Polarization in K + → p 0 m + n Decays at J-PARC. Suguru SHIMIZU Osaka University. Transverse muon polarization. K + → p 0 m + n decay. T-odd.

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Measurement of T-violating Transverse Muon Polarization in K + → p 0 m + n Decays at J-PARC

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  1. Oct. 6, 2006 SPIN2006 Measurement of T-violating Transverse Muon Polarization in K+→p0m+n Decaysat J-PARC Suguru SHIMIZU Osaka University

  2. Transverse muon polarization K+→p0m+ndecay T-odd • Spurious effects from final state interaction are small.Non-zero PTis 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) PT = - 0.0017 ± 0.0023(stat) ± 0.0011(syst) ( |PT| < 0.0050 : 90% C.L. ) PRD73, 72005(2006)

  3. Matrix element of K+→p0m+n decay Im(ξ)≠0 T-violation T-violation parameter : Im(ξ) PT is sensitive to scalar couplings.

  4. Beyond the Standard Model • Standard Model contribution to PT: • Only from vertex radiative corrections andPT(SM) < 10-7 • Spurious effects from final state interactions (FSI) • Recent elaborate calculation :PT(FSI) < 10-5 • There is a large window for new physics beyond the SM in the region of PT = 10-3 ~ 10-5 • There are theoretical models which allow sizeable PT without conflicting with other experimental constraints.

  5. Model descriptions of PT • Multi-Higgs doublet (3 Higgs doublet) model (MH) • Imx = (mK2/mH2) Im(g1a1*) • | Im(g1a1*) | < 544 (mH/GeV)2 from the E246 limit • B→tnX constraints also Im(g1a1*) but weaker ( <1900 (mH/GeV)2 ) • N-EDM and b→sg constraint differently Im(a1b1*) • SUSY with s-quark mixing (SUS) • Imx ∝ Im[V33H+V32DL* V31UR*]/ mH2 • mH ≥ 140 GeV from the E246 limitand no stringent limit from other modes • SUSY with R-parity violation (SUR) • Imxl ~ Im [l2i2(li12)*], Imxd ~ Im [l’21k(l’22k)*] • No stringent limits from other modes

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

  7. B Determination of PT Stopped K+ beam Double ratio measurement • ＋PT(π0 forward)＝－PT(π0 backward) • PN contribution to systematic error is • drastically reduced.

  8. E246 result • 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. ) PRD73, 072005(2006) Statistical error dominant

  9. New experiment at J-PARC • We aim at a sensitivity of dPT ~10-4 (E246-dPT ~10-3) • Statistical errordPTstat ≤0.1 dPTstat (E246) ~10-4 with 1) ×30 of beam intensity, 2) ×10 ofdetector acceptance Systematic error dPTsyst ~ 0.1 dPTsyst (E246) ~10-4by 1) precise calibration of misalignments using data 2) correction of systematic effects JPARC

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

  11. 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

  12. Active polarimeter • 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 drift 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/R positron • Fit for p0fwd/bwd measurement

  13. Muon field magnet • Uniform field of0.03 T • Precise field alignment of 10-3 • Gap : 30 cm • Pole face : 60 cm ×40 cm • No. of coils : 24 • Mag. motive force : 3.6×103 A Turn/coil 20 cm

  14. Systematic error from B field rotation Side View End View B PNfwd spectrometer PNfwd Left Right m+ • muon field magnet • Active polarimeter Left Right B PTbwd PNbwd PTfwd PNbwd p0 fwd p0 bwd π0 fwd 1+a PT bwd 1-a PT π0 fwd 1+b PN bwd 1-b PN fwd/bwd = 1+2aPT fwd/bwd = 1+2bPN ≠1 systematic error Calibration of the polarimeter is very Important.

  15. Calibration of four misalignments er Pr PL dr • Polarimeter left/right asymmetry measurement using • longitudinal pol. PL K+→m+n (Km2 ) • radial polarization Pr from K+→p0p+(Kp2 )-p+ decay in flight ez dZ • A(PL)= (er-dr )coswt + (ez-dz) sinwt + dr • A(Pr)= (er-dr) sinwt- (ez-dz) coswt + dz • Unique determination of • er ez dr dz • with an accuracy of ~10-4 dangerous

  16. MC results: calibration of misalignments PL Pr L:black R: red er=(3.7±0.2) x 10-3 ez=(4.0±0.2) x 10-3 dr=(3.9±0.2) x 10-3 dz=(3.7±0.2) x 10-3with use of 108 muons Km2: 1 day collection Kp2: simultaneous data collection with Km3 4 rotations

  17. Target and tracking • Addition of C0 and C1 • GEM chambers with • -high position resolution • - higher rate performance • Larger C3-C4 • distance • Use of He bags E246 J-PARC • Better kinematical resolution • Stronger Kp2difm+ BG suppression • New target

  18. MC studies of tracking Km3 Kp2-dif • Four chamber tracking including C0 with 0.1mm resolution Suppression of Kp2-dif down to ~1.0% • Remaining BG is from the p+ decay between the target and C0. • Further suppression down to 0.1% level with the fit trajectory consistency with target fibers, and target fiber analysis. dPT (pm2 BG) < 10-4

  19. Beamline for K+ extraction K0.8 ( K1.1-BR) proton K0.8 Momentum 800 MeV/c Momentum bite ±2.5% Acceptance 6.5 msr % Dp/p K+ intensity 3 ×106 /s K/p ratio > 2 Beam spot 1.04 ×0.78 cm (FWQM) Final focus achromatic

  20. Sensitivity estimate Statistical sensitivity Systematic errors Source dPT dz < 10-4 qz < 10-4 qe+, Ee+ < 10-4 Source dPT • Net run time 1.0 ×107 s • Proton beam intensity 9mA on T1 • K+ beam intensity 3×106 /s • Total number of good Km3 2.4×109 • Total number of fwd/bwd (N) 7.2×108 • Sensitivity coefficient 3.73√N Total ~ 10-4 Total ~ 10-4 JPARC

  21. Summary • PT in Km3 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 dPT ~ 10-4. • New K0.8 beamline • Upgraded E246 detector • Stage 1 approval • Upgrade will be finished by 2010. • Data taking will be started from 2011.

  22. Collaboration(present group) • Beamline • Target • GEM chambers • Tracking upgrade • Canada U.Saskatchewan TRIUMF UBC U. Montreal • USA MIT U. South Carolina Iowa State U. • Japan KEK Tohoku U. Osaka U. NDA • Muon field magnet • Active polarimeter • CsI(Tl) readout • DAQ We will organize more people after obtaining an approval.

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