Result of T-violating Muon Polarization Measurement in the K + →  0  + Decay J. Imazato IPNS, KEK for the KEK-E246 collaboration March 21, 2004 XXXIXth Rencontres de Moriond Transverse muon polarization E246 experiment Analysis Result of the total data

E246 collaboration Japan ● KEK ● Univ. of Tsukuba, ● Tokyo Institute of Technology ● Univ. of Tokyo ● Osaka Univ. Russia ● Institute for Nuclear Research Canada ● TRIUMF ● Univ. of British Columbia ● Univ. of Saskatchewan ● Univ. of Montreal Korea ● Yonsei Univ. ● Korea Univ. U.S.A. ● Virginia Polytech Institute ● Princeton Univ. Taiwan ● National Taiwan Univ.

Transverse Muon Polarization in K + →  0  + K  3 decay form factors and T violation History of K  3 transverse polarization experiments K L →  −  + Bevatron 1967 Im  = ±0.08 K L →  −  + Argonne 1973 Im  = ±0.064 K L →  −  + BNL-AGS 1980 Im  = ±0.030 K + →  0  + BNL-AGS 1983 Im  = ±0.025

Feature of K +  P T ■ Small standard model contribution – Bigi and Sanda “CP violation” (2000) – P T ~ ■ Small FSI spurious effects –Single photon contribution Zhitnitskii (1980) P T < ~ –Two photon contribution Efrosinin et al. PL B493 (2000) 293 P T ~ 4 x ■ High sensitivity to CP violation beyond the SM – Mult- Higgs doublet model – Leptoquark model – Some Supersymmetric models P T ~ Three Higgs doublet model SM FSI (example)

KEK E246 experiment ■ Stopped K + experiment with a SC toroidal spectrometer ■ Measurement of all decay kinematics directions –Double ratio measurement with small systematic errors Features History ■ : detector construction ■ : data taking ■ 1999 : first result published with 1/4 of data Im  = ± 0.007(stat) ± 0.003(syst) [M.Abe et al., Phys.Rev.Lett. 83(1999) 4253] ■ : analysis ■ 2004 (this conference) : report of the final result Byproducts ■ K + →    P T = ± (stat) ± (syst) [V.Anisimovsky et al., Phys.Lett. B562 (2003) 166] ■  e3    e4 

Superconducting toroidal magnet

E246 experimental setup End viewSide view [J.Macdonald et al.; NIM A506 (2003) 60] K + →  0  +

E246 detector

Muon polarimeter Cross section One-sector view y(cm)

CsI(Tl) and kinematics CsI barrel fwd and bwd  0 /  P T directions fwd -    bwd -    Double ratio measurement

Experimental data K +  3 event selection e + time spectra CsI(Tl) analysis :  TOF analysis Momentum analysis e + time spectrum

Analysis K  3 event selection e + time spectrum anlysis Asymmetry analysis A T (y)=[A(y) fwd - A(y) bwd ] /2 [N cw (y)-N ccw (y)] f(b) A(y) f (b) = [N cw (y)+N ccw (y)] f(b) P T (y) =A T (y) /  (y)  (y) = A N (y) / P N P T = ∫ P T (y) w (y)dy Im  = P T / fwd events : cos   0 (  ) > bwd events : cos   0 (  ) < ⇒ N cw(ccw) : integration from 20ns to 6  s with constant BG subtracted =2  ; o=1 

Two independent analyses ■ Two analyses by two teams with their own analysis policy and event selection methods Comparison of good K  3 event e.g. :  events 1  events A k 1264 k A1 918 k 909 k ■ Combination of the two analyses by resorting of events to 6 data sets — A1 A2 A1 A2 A1 A2 — 22 11 Merits of two analysis method Cross check of data quality by A 0, decay plane rotation  r and  z and P T Comparison of sensitivity by normal asymmetry A N and Check of data quality in e.g. A1 by comparing A1 A2 and A1 A2-bar Estimate of systematic error by comparing of A1 A 2 from A1 and A2 Improvement of statistical error

Data quality check Null asymmetry check A 0 =[(N cw /N ccw ) total -1]/2 Sensitivity check A N =(A left - A right )/2 A left = [(N cw /N ccw ) left -1]/2 A right = [(N cw /N ccw ) right -1]/2 total = fwd + bwd 6 data sets for each period Open circles are 2  events and dots are 1  events. Null asymmetry is canceled by double ratio ( fwd-bwd ).

Result P T = ± (stat) ± (syst) ( |P T | < : 90% C.L. ) Im  = ± (stat) ± (syst) ( |Im  | <0.016 : 90% C.L. )

Systematics check ● = ; o=1998; ★ = Im  = ±    d.o.f  ● = 2  ; o =1  ; Consistency among data Sector dependence Decay plane rotation  r (fwd)-  r (bwd)  ≤ 4.6×10 -4 rad  z (fwd)-  z (bwd)  ≤ 2.6×10 -4 rad

Systematic errors Source of Error  12fwd/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--38 Total11.4  12 : 12-fold rotational cancellation fwd/bwd :  0 forward/backward cancellation

Model implications L = (2√(2)G F ) 1/2  [  i U L KM D D R +  i U R M U KD L +  i N L M E E R ] H i + + h.c. Im  = Im(  1  1 * ) × ( v 2 / v 3 ) 2 × (m K / m H + ) 2 = Im(  1  1 * ) × (m K / m H + ) 2 v i : vacuum expectation values  i,  i,  i : mixing matrix elements Three Higgs doublet model |Im  | < (90% C.L.) ⇒ Im(  1  1 * ) < 544 (at m H =m Z ) cf. BR (B→X   ) ⇒ Im(  1  1 * ) < 1900 (at m H =m Z ) Neutron EDM in 3HD model d n ≈ 4/3 d d ∝ Im(  1  1 * ) × m d / m H 2 v 2 / v 3 = m t /m  [R.Garisto and G.Kane, Phys. Rev. D44 (1991)2789 ] |Im  | < (90% C.L.) ⇒ d n < 9 × e cm cf. d n exp < 6.3 × e cm −

Summary ■ Transverse muon polarization in K + →  0  + decay is a good probe of CP violation beyond the standard model. ■ The final result of the KEK-E246 experiment showed no evidence for T violation with Im  = ± (stat) ± (syst), or |Im  | <0.016 (90% C.L. ). ■ This limit constrains the parameters of some non-standard CP violation models with high sensitivity. ■ We are going to propose a next generation P T experiment at the high intensity accelerator J-PARC.

Decay plane rotation = = ±0.12 mr 0.02±0.14 mr = = 0.27±0.48 mr -0.20±0.58 mr

B field rotation

CsI(Tl) photon detector Segmentation  =  = 7.5 o Number of crystals 768 Length of crystals 25 cm (13.5 X 0 ) Inner radius 20 cm Outer radius 50 cm Solid angle ~75%of 4  Readout PIN diode Light yield p.e./MeV Equiv. noise level 65 keV [D.V.Dementyev et al. Nucl. Instr. Method A440 (2000) 151]

Double ratio measurement

Analysis: methodology Blind analysis ■ Event selection optimization before looking at A T Two independent analyses ■ Easy to find any trivial mistakes in data reduction and analysis codes ■ Competition with each other for better analysis codes ■ Minimize potential human bias in the analysis Combination of two results ■ Analysis of “common” and “uncommon” events to check the event quality ■ Makes it possible to estimate systematic error associated with analysis ■ Improves the statistical accuracy

1998 data:  0 mass spectrum comparison with