TREK experiment
to search for T violation
in kaon decays
at J-PARC
J.Imazato
KEK & J-PARC
June 9, 2009
KAON 09 Conference

TREK/E06
Time Reversal Experiment with Kaons:Search for New Physics beyond the Standard Model by
Measurement of T-violating
Transverse Muon Polarization (PT) in K+ ! µ+!0! Decays

K+ ! µ+!0!
New official website:

http://trek.kek.jp2Outline" Transverse µ+ polarization (PT ) in Kµ3" Theoretical models" Current experimental status" J-PARC TREK experiment" Detector upgrade" Sensitivity" Summary

TREK collaboration
CANADA

JAPAN

University of Saskatchewan
Department of Physics and Engineering
University of British Columbia
Department of Physics and Astronomy
TRIUMF
Universite de Montreal
Laboratoire de Physique Nucleaire

Osaka University
Department of Physics
National Defense Academy
Department of Applied Physics
Tohoku University
Laboratory of Nuclear Science
High Energy Accel. Research Org. (KEK)
Institute of Particle and Nuclear Studies
Institute of Material Structure Science
Accelerator Laboratory
Kyoto University,
Department of Physics
Tokyo Institute of Technology (TiTech)
Department of Physics

USA
Massachusetts Institute of Technology (MIT)Laboratory for Nucl. Science & Bates Lin. Acc. Center
University of South Carolina
Department of Physics and Astronomy
Iowa State University
College of Liberal Arts & Sciences
Hampton University
Department of Physics
Jefferson Laboratory

VIETNAM
University of Natural Sciences

RUSSIATHAILAND

Russian Academy of Sciences (RAS)
Institute for Nuclear Research (INR)

Kasetsart University
4Transverse µ+ polarization (PT) in "µ3
K+!#0µ+! decay" PT is T-odd, and spurious effects from final state interaction
are small: PT (FSI) < 10-5
Non-zero PT is a signature of T violation.
" Standard Model (SM) contribution to PT : PT (SM) < 10-7

PT in the range 10-3 ~10-4 is a sensitive probe of
CP violation beyond the SM.
" There are theoretical models of new physics which allow
a sizable PT without conflicting with other experimental
constraints.

5Exotic scalar interactions
Kinematic factor" Generic four fermion interaction Lagrangian analysis" Effective field theory with Wilson coefficients|ImGs| / GF|(m CS| (!/TeV)2!"#$%&!'< 2.2 x 10-4! 2 x 10-3

< 1x 10-5! 1 x 10-4

" Typical models with scalar interactions allowing
a sizable PT :– Multi-Higgs doublet model– SUSY with R-parity violation or large squark mixing

6Three Higgs doublet model

$1%1

•

c.f. dn , b!s$ " Im(%1&1*), (%1&1*)

nroteuNMEDb!

s$B!X'!

E246

22Im(%1&1*) = -v___
2 /v3 Im($1%1*)

Higgs field v. e. v.

TREK goal" B!X'! and B!'! at Super-Bellecorresponds to PT < 3 x 10-4
c.f. TREK goal : PT ! 1 x 10-4

v2/v3 = mt / m'

" PT is the most stringent constraint for Im($1%1*)

7

SUSY with R-parity violation
Super potential : W = WSMMS + WRPV
Im( = Im (l + Im (d’ 2k |)2*|)’ 21k)’ 312||)* 232
E246
Relevant parameters and constraints

TREK"PT is a very stringent constraint for these parameters !

8

PT measurement
K+!#0µ+!

Use of upgraded E246 detector
Active polarimeter
Fiber target

C0,C1 GEM

CsI(Tl) readout" PT is measured as the azimuthal asymmetry Ae+of the µ+ decay positrons

Superconducting toroidal magnet

9Stopped beam method
Double ratio experiment
AT = (Afwd - Abwd ) / 2Afwd(bwd) =Ncw - Nccw
Ncw + Nccw

PT = AT / {% <cos+T>}% : analyzing power<cos+T> : attenuation factor

Im( = PT / KF : physics parameter
KF : kinematic factor

Current limit from E246

bwd -#0 ($ )fwd -#0 ($ )PT = - 0.0017 ± 0.0023(stat) ± 0.0011(syst)( |PT | < 0.0050 : 90% C.L. )Im( = - 0.0053 ± 0.0071(stat) ± 0.0036(syst)( |Im( | <0.016 : 90% C.L. )PRD 73, 072005 (2006)" E246 was Statistical error dominant

11J-PARC TREK Experiment" Stopped K+ method with SC Toroidal Magnet" Upgraded E246 detector" Sensitivity goal : ,PT ~10-412

Active muon polarimeter" Full angular acceptance for positronse+higher statistics" Determination of decay vertex
lower background" Measurement of e+ angle and approx.
energyhigher analyzing power" Improved field alignment
suppressed systematic error

Gap wire chambers
Number of plates 24
Plate material
Al, Mg or alloy
Plate thickness~ 2.5 mm
Plate gap
~ 8 mmAve. density
0.24 .Al+µ stop efficiency ~ 85%" Prototype chambers are currently made and testedMuon field magnet for TREK
" Control of muon spin motion
0.03 T" Decoupling of stray field~0.3 G / 300 G ~ 10-3
" Mechanical alignment of the 300 Gfield,P - ,+ " 10-3
" Further alignment using Kµ3 data
,P ~ ,+ " 10-4

Muon Field Magnet
Field srength0.03 TGap
31 cm
Pole face
68 # 44 cm
Number of coils 24
Total power
20 kW
Coolingindirect water" High-precision magnets with good symmetry are being made13

Tracking system" Higher kinematic resolution" Better K#2 background suppression

E246

J-PARC E06" New C0 (cylindrical) and C1(planer) are GEM chambers

15

Active fiber target
Cross section

1. Finer segmentation for" Higher µ+ tracking resolution" Higher K+ stop point resolution" K#2 background suppression(E246 : 256 fibers with 5 x5 mm2)µ+

3 x 3 mm
492 fibers
12
timingcounters
for timing

2. Compact and light system" using SiPMT (MPPC)(E246 : each fiber was read by a1/2” PMT)One element

Current baseline design" Beam test of MPPC damage was performed using pions

16

MPPC deterioration by irradiation" Irradiation test under the realistic beam halo condition" 100 MeV/c #+ beam at TRIUMF

No irradiation

14.4 x108 pions(20.5 TREK-yrs)

3.38 x108 pions(4.8 TREK-yrs)

31.4 x108 pions(44.6 TREK-yrs)

10.2 x108 pions(14.5 TREK-yrs)

51.8 x108 pions(73.6 TREK-yrs)(1.4 x108 protons)" It was shown that MPPC has long enough lifetime

C0 Cylindrical GEM for TREK" Suppression of K#2 BG: as close to the target as possible" Complete rotational symmetry : seamless structure

140 mm

160 mm

300 mm" High position resolution; , < 0.1 mm" Very high rate capability; 25 kHz/mm2" Radiation-hardness ; 4 x1010 MIPs/mm2" TREK: Rates <250 Hz/mm2 (halo < 5 Hz/mm2),
Total dose: 7 x107 particles

18

APD readout of CsI(Tl)" Improvement of timing and rate performanceby using APD diodes and FADC

too slow

One module test with a new amplifier

new requirement : > 10 times faster

Typical pileup signals(FADC spectra) in one
modue test with e+beam:" Pileup signal could be analyzed resulting ingood high rate performance19

E246 systematic errors
Source of Error/12fwd/bwd,PT x 104

e+ counter r-rotatione+ counter z-rotatione+ counter 0-offset
e+ counter r-offset
e+ counter z-offsetµ+ counter 0-offset
MWPC 0-offset (C4)
CsI misalignment
B offset (1)B rotation (,x)
B rotation (,z)
K+ stopping distributionµ+ multiple scattering
Decay plane rotation (+r)
Decay plane rotation (+z)
K#2 DIF backgroundK+ DIF background oAnalysis -xxxooxxoxxxoxxxxxooooooooooxoxoxo0.5
0.2
2.8<0.1<0.1
<0.1
2.0
1.6
3.0
0.4
5.3
<3.0
7.1
1.2
0.7
0.6
< 1.9
3.8

Total

11.4

" Cancellation by/12
and/orfwd/bwd almost
all systematics
except for :µ+ field alignmentµ+ multiple scattering
decay plane shifts
due to" K+ stopping distribution" Detector inefficiency
distribution etc.

"Systematic error will be suppressed to 1/10 in TREK

20

Misalignment analysis using Kµ3" Asymmetry analysis in termsof +0 : in-plane spin angle fromz-axis

small residualof oscillation

Asub(+0)

Asum(+0)

PTIm(=0.05PT+,zPT+,rPT+,z+,r" Asub(+0 ) is independent of polarimeter misalignments

21

Expected sensitivity in TREK$,PTstat ! 0.05 ,PTstat (E246) !10-4 : 1.4 x 107 sec of run

1) # 30 beam intensity2) # 10 detector acceptance3) Higher analyzing power" ,PTsyst ! 0.1 ,PTsyst (E246)!10-41) Precise calibration misalignments
2) Correction of systematic effects
3) Precise fwd-bwd cancellation

Very schematic"We aim at a sensitivity of ,PT ~10-422K0.8 (K1.1-BR) for stopped K+" Low momentum (p=0.8 GeV/c) separated beam
" Macroscopic time sharing with K1.1 once it is installed
T1

K1.1BRKLK1.1

TREK" IK+ = 2.1 # 106 /s @ 9 µA- 30 GeV protons on T1" K/# ratio > 1.0" The beamline will be completed in 201023

TREK time schedule" 2006: Proposal and Stage-1 approval" 2007-2010 : Detector R&D,
Construction of Active polarimeter" 2009: Budget request for detector" 2009-2010 : Construction of the K0.8 beamline" 2010-2012 : Detector construction" 2012-2013 (?) : RunMore than 100 kW of beam power is necessary24Summary" Transverse µ+ polarization in K+-> #0µ+! decay is asensitive probe of new physics through CP violation
beyond the SM.
" J-PARC TREK experiment aims at a sensitivity of 10-4
improving the current limit from KEK E246 by a factor
more than 20.
" An upgraded E246 detector and a stopped K+ beam
method are employed to realize the smallest possible
systematic error.
" Currently the active polarimeter is under construction.
" We aim to run the experiment in the early stage of
J-PARC operation in the near future.