for the E06(TREK) collaboration May 21-25, 2007 KAON’07, Frascati Measurement of T-violating transverse muon polarization in K+→p0m+n decay at J-PARC Suguru SHIMIZU Osaka University for the E06(TREK) collaboration

RE collaboration T K Japan: Canada: US: Russia: Vietnam: Osaka University National Defense Academy (NDA) Tohoku University KEK Canada: University of Saskatchewan University of British Columbia (UBC) University of Montreal TRIUMF US: MIT University of South Carolina (USC) Iowa State University (ISU) Russia: Institute for Nuclear Research (INR, Russia) Vietnam: University of Natural Sciences (UNS, Vietnam)

Transverse muon polarization K+→p0m+n decay T-odd Non-zero PT is a signature of T violation. Standard model contribution is very small(10-7). Spurious effect from final state interaction is also small(10-5). Therefore, PT is sensitive to physics beyond the Standard Model. Experiment at KEK(E246) PT = - 0.0017 ± 0.0023(stat) ± 0.0011(syst) ( |PT | < 0.0050 : 90% C.L. ) PRD73, 72005(2006)

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 limit and 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

KEK-PS E246 experiment PT = - 0.0017 ± 0.0023(stat) ± 0.0011(syst) Stopped K+ method Toroidal Spectrometer and CsI(Tl) calorimeter Measurement of e+ asymmetry in cw/ccw direction decay side view end view PT = - 0.0017 ± 0.0023(stat) ± 0.0011(syst) Imx = - 0.0053 ± 0.0071(stat) ± 0.0036(syst)

New experiment at J-PARC (TREK) We aim at a sensitivity of dPT ~10-4 (E246-dPT ~10-3) Reasonable upgrading of the E246 system Statistical error dPTstat ≤ 0.1 dPTstat (E246) ~10-4 with 1) × 30 of beam intensity → rate capability of detectors 2) × 10 of detector acceptance Systematic error dPTsyst ~ 0.1 dPTsyst (E246) ~10-4 by 　 1) precise calibration of misalignments using data 2) correction of systematic effects JPARC

Upgrade of the E246 detector for TREK at J-PARC Muon polarimeter passive → active Muon magnetic field toroid → muon field magnet Target smaller and finer segmentation MPPC readout Charged particle tracking addition of GEM around target CsI(Tl) readout PIN → APD with current amplifier

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 Lower BG in positron spectra Parallel plate stopper with Gap MWPC 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 ~ 95% Small systematics for L/R positron

PT determination p0 fwd/bwd scheme B field preserves PT component. PT(fwd) = - PT (bwd) p0 left/right scheme PT component is rotated by the field. PT (left) = - PT (right) left e+ detection If the finite PT contributes, bwd-fwd bwd+fwd left-right left+right fwd m+ spin bwd right Z Y

Beamline for K+ extraction K0.8 ( K1.1-BR) proton Final Focus 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 Single stage DC separator Vertical focuses before and after the separator Horizontal focus just after the second D-magnet

Systematic error from B field rotation Side View End View B PNfwd spectrometer PNfwd Left Right m+ Left Right B PNbwd PTfwd PTbwd 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 misalignment using experimental data is very important. 1m rad. uncertainty of B fieldD PT = 10-3

Cancellation mechanism for misalignments q0 : the muon spin phase at t=0 Asym. Km3 MC, Non-zero PT Km3 MC, PT=0, δz=5deg π0 bwd π0 bwd π0 fwd π0 fwd q0 (deg) q0 (deg) A(q0)fwd≠ A(q0)bwd A(q0)fwd= A(q0)bwd = drcosq0-dzsinq0 Careful MC studies for systematic errors

Sensitivity estimate of TREK Statistical sensitivity Systematic errors Source dPT Net run time 1.0 ×107 s　 -- one year run Proton beam intensity 9mA on T1 K+ beam intensity 3×106 /s -- 30 times of E246 Total number of good Km3 2.4×109 -- detector acceptance: 8 times of E246 Total number of fwd/bwd (N) 7.2×108 Sensitivity coefficient 3.73√N -- Analyzing power: 1.5 times of E246 Total ~ 10-4 Source dPT field alignment 　　 < 10-4 kinematic distortion < 10-4 polarimeter analysis < 10-4 Total <10-4 JPARC

Summary We aim at a sensitivity of dPT ~10-4 for statistical and systematic errors. New K+ beam line (K0.8). Reasonable upgrading of the E246 system, (1)active polarimeter, (2)readout of calorimeter, (3)tracking system. Careful check of systematic errors by MC. Test of the new detector component. Now stage-1 is approved, next step is stage-2 approval

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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

Status of TREK Stage-1 approval in the first PAC meeting in June-July, 2006. Now; Studies of detector upgrade Polarimeter alignment procedure Muon field magnet Seek for funding Grouping 〉 Most important issues