Hisaki Hayashii (NWU, Japan) for the Belle collaboration Measurement of the electroweak properties of t leptons in the Belle experiment (Precise measurement of t lepton lifetime ) Hisaki Hayashii (NWU, Japan) for the Belle collaboration July 2014, Valencia, Spain

Contents Introduction: Lepton universality Precise measurement of tau lifetime Method Systematics Results Discussion 2014/7/5 ICHEP 2014, Valencia, Spain

Introduction Motivation Precise measurement of the t lifetime is necessary for the tests of lepton universality that is assumed in the SM. W/o assuming lepton universality, leptonic branching fractions and lifetimes are given for L=t, m by The ratios of the couplings are t lifetime, ,plays an important role for lepton universality test. 2014/7/5 ICHEP 2014, Valencia, Spain

Tau lifetime, motivation Present status 2.6 s deviation from the Standard Model S. Schael et al. Phys. Rep. 532, 119 (2013) 2014/7/5 ICHEP 2014, Valencia, Spain

Measurement of tt at Belle Belle vertex detector Very small amount of material 2.7 % X0 : including beam pipe + SVD + drift chamber inner cylinder Impact parameter resolution Two configurations: Vertex detector 1 : 1st 157/fb data 3 double side Si detector (SVD1) Beam pipe: 2.0 cm diameter Vertex detector 2 : remaining 554/fb data 4 double side Si detector (SVD2) Beam pipe: 1.5cm diameter Multiple scattering effects Double side Si detector: Each layer provides both r-f and z coordinates. 2014/7/5 ICHEP 2014, Valencia, Spain

Method of tt measurement (1) We analyze events These events allow to reconstruct t+ and t- decay points in 3 dimensions (V1, V2) Each t momentum direction in CMS is determined from the energy and mass of 3p system with two-fold ambiguity. Using known boost factor, the momentum directions in Lab for t+ and t- are determined. In CMS 2014/7/5 ICHEP 2014, Valencia, Spain

Method of tt measurement (2) Knowing the decay points and momentum directions for both t’s, asymmetric-energy layout allows to determine the t+t- production point (shown by V01, V02 ). Note dl=|V01-V02|=0 for ideal case. We use average points among two solutions . The decay times for t+ and t- are reconstructed as Lab. frame where No information about the beam spot position is needed in this approach !! dl =0 for ideal case 2014/7/5 ICHEP 2014, Valencia, Spain

Data and selection Data sample L=711fb -1 (Y(4S) data ) Thrust >0.9, separate two hemispheres in CMS. 3 charged pion for both sides. No p0, Ks, Ng<6 with Egtot<0.7GeV Pt2(6p)>0.25GeV2, 4 GeV < M(6p) < 10.25 GeV to suppress 2g and other background . Pseudomass Good vertex-fit quality χ2<20 Minimum distance between t+ and t- in Lab., dl<0.02cm. 1,148,000 (3p)- nt, (3p)+ nt sample with small background contamination. Main backgrounds are from Mmin dl 2014/7/5 ICHEP 2014, Valencia, Spain

Data model and linearity Resolution function (MC) Fitting form R(t-t’) detector resolution function Modified Gaussian, 4 parameters to parameterize s. Auds: e+e-qq (q=uds) background: 2% Bcb: e+e-qq (q=c,b) background: 0.2% lt:estimator of ctt The offset is determined by simulation from the true vs rec. relation. 2014/7/5 ICHEP 2014, Valencia, Spain

Fit result From the fit of the experimental data and using , we obtain 711 fb-1 Points: Data Solid line: Fit Red histogram: uds background Magenta line: fit to uds backg. Blue histogram: charm backg. Blue line: fit to charm backg. From the fit of the experimental data and using , we obtain uds charm 1 mm 2014/7/5 ICHEP 2014, Valencia, Spain

Systematic uncertainty (1) Source Δτ (mm) SVD alignment 0.090 Resolution fucntion 0.030 Beam energy and ISR description 0.024 Fit range 0.020 Background contribution 0.010 t- lepton mass 0.009 Total 0.101 (0.12 %) Si vertex detector(SVD) alignment SVD is aligned by using cosmic-rays. Effects from uncertainty of the both local and global alignment are taken into account. local uncertainty: shifts (10 mm ), rotation(0.1mrad) global uncertainty w.r.t. drift chamber: shift(20 mm), rotation(1mrad). For cross check, i) divide data into two different samples by azimuthal (f) angle. ii) Results from two SVDs (SVD1 and SVD2): -> These provide consistent results within stat. errors. Resolution function (0.12%) 2014/7/5 ICHEP 2014, Valencia, Spain

Systematic uncertainties (2) Resolution functions: Two different forms are tried for resolution functions ISR effects. Use KKMC. ISR simulation is cross checked by e+e-→　m+m- data Background -50% + 150 % uncertainties are assumed for e+e-qq Dependence on the event selection. It is found that the correction factor depends slightly on the value of dl cut. But the resultant value of t lifetime after correction is quite stable for different cuts on dl. Other selection　criteria are negligible effect. (0.12%) Resultant total systematic uncertainty is 0.12 % 2014/7/5 ICHEP 2014, Valencia, Spain

Belle t life time results Almost twice more precise than the current world average. This result is statistically limited yet. Repeated analysis in Belle II, increased statistics and better vertex detector, can improve the accuracy of the measurement. 2014/7/5 ICHEP 2014, Valencia, Spain

Discussion Test of the Lepton universality Lepton universality is tested at 1.6 per mill level. SM 2014/7/5 ICHEP 2014, Valencia, Spain

Lifetime difference for t+ and t- lifetime difference (CPT test) t lifetime difference is measured for the first time. ( Possible only at the asymmetric-energy collider.) Note that t+ t- mass difference is tested at the 10-4 level by B-factory exp. 711 fb-1 t- : open points t+ : solid points 2014/7/5 ICHEP 2014, Valencia, Spain

Summary With 711fb-1 data, Belle measures t lifetime and the upper limit on the relative lifetime difference between t+ and t- . New result is almost twice more precise than the current world average. The lifetime difference has been measured for the first time. See PRL 112, 031801 (2013) for details. Other new results of EW properties of t lepton with full Belle statistics come soon t → m g, e g lepton-flavor violating decays t lepton Michel parameters t lepton electric dipole moment (EDM) Stay tuned. 2014/7/5 ICHEP 2014, Valencia, Spain

Backup 2014/7/5 ICHEP 2014, Valencia, Spain

Tau mass measurement at Belle PRL 99. 011801 (2007) 2014/7/5 ICHEP 2014, Valencia, Spain

Precision studies of t properties at B-factories Tau lifetime: Belle: PRL 112, 031801 (2013) Tau mass: Belle: PRL 99. 011801 (2007) Babar: PRD 80, 092005(2009) Tau electric dipole moment(EDM) Belle: PLB 551, 16 (2003) based on 29.5fb-1 data Lepton universality Babar: PRL 105, 051602 (2010) Michel parameters in This talk With full data, coming soon Coming soon ICHEP 2014, Valencia, Spain 2014/7/5