Measurement of T-violating Transverse Muon Polarization in

+→ Decaysat J-PARC

Suguru SHIMIZUOsaka University

Oct. 6, 2006SPIN2006

Transverse muon polarization

Spurious effects from final state interaction are small. Non-zero PT is 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)

K+→decay

T-odd

Matrix element of K+→ decay

PT is sensitive to scalar couplings.

T-violation parameter : Im(ξ) Im(ξ)≠0 　 　 T-violation

Beyond the Standard Model Standard Model contribution to PT :

– Only from vertex radiative corrections and PT(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.

Model descriptions of PT Multi-Higgs doublet (3 Higgs doublet) model (MH)

– Im = (mK2/mH

2) Im(11*)

– | Im(11*) | < 544 (mH/GeV)2 from the E246 limit

– B→X constraints also Im(11*) but weaker ( <1900 (mH/GeV)2 )

– N-EDM and b→s constraint differently Im(11*)

SUSY with s-quark mixing (SUS)– Im ∝ Im[V33

H+ V32DL* V31

UR*]/ mH2

– mH ≥ 140 GeV from the E246 limit and no stringent limit from other modes

SUSY with R-parity violation (SUR)– Iml ~ Im [2i2(i12)*], Imd ~ Im [’21k(’22k)*]– No stringent limits from other modes

• Stopped K+ method• Large solid angle and high resolution of Toroidal Spectrometer and CsI(Tl) calorimeter

side view end view

decay

T-violation search in KEK E246 experiment

Double ratio measurement ＋ PT(π0 forward) ＝　－ PT(π0 backward)

PN contribution to systematic error is drastically reduced.

Determination of PT

Stopped K+ beam B

E246 result

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. )Statistical error dominant

AT = (Afwd - Abwd ) / 2

Ncw - NccwAfwd(bwd) = Ncw + Nccw

PT = AT / {<cosT>} : analyzing power <cosT> : attenuation factor Im = PT / KF

KF : kinematic factor

PRD73, 072005(2006)

New experiment at J-PARC We aim at a sensitivity of PT ~10-4 (E246-PT ~10-3)

Statistical errorPT

stat ≤ 0.1 PTstat (E246) ~10-4 with

1) × 30 of beam intensity, 2) × 10 of detector acceptance

Systematic errorPT

syst ~ 0.1 PTsyst (E246) ~10-4 by

　 1) precise calibration of misalignments using data 2) correction of systematic effects

JPARC

Method of experiment Stopped K+ decay

– Superior to in-flight decay Toroidal spectrometer

E246 detector upgrade–Well known performance–Well studied systematics–Good alignment in magnet and CsI(Tl)–Lower cost

FoM (A√N) distribution

Detector acceptance

Upgrade of the detector

Muon polarimeter passive → active

Muon magnetic field toroid → muon field magn

et Target

smaller and finer segmentation

Charged particle tracking addition of two chambers

CsI(Tl) readout PIN diode → APD

New analysis scheme

Active polarimeter Identification of muon stopping point/ decay vertex Measurement of positron energy Ee+ and angle e+ Large positron acceptance of nearly 4 Larger analyzing power Higher sensitivity Lower BG in positron spectra

Parallel plate stopper withGap drift chambers Number of plates 31 Plate material Al, Mg or alloy Plate thickness ~ 2 mm Plate gap ~ 8 mm Ave. density 0.24 Al

stop efficiency ~ 85%

Small systematics for L/R positronFit for 0 fwd/bwd measurement

Muon field magnet

Uniform field of 0.03 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

Systematic error from B field rotation

• muon field magnet• Active polarimeter

fwd

bwd

PN

fwd

PNbwd

spectrometer

Side View End View

PNfwd

PNbwd

Left RightLeft Right

B

π0 fwd 1+ PN

bwd 1 PN

fwd/bwd = 1+2PN ≠1

systematic error

Calibration of the polarimeteris very Important.

BPT

fwd PTbwd

π0 fwd 1+ PT

bwd 1 PT

fwd/bwd = 1+2PT

Calibration of four misalignments

Polarimeter left/right asymmetry measurement using

longitudinal pol. PL K+→ (K2 )

radial polarization Pr from K+→(K2 )-+

decay in flight

PrPL

dangerous

A(PL)= (r r )cost + (z-z) sint + r A(Pr)= (rr) sint (z-z) cost + z

Unique determination ofr z r z

with an accuracy of ~10-4

r

r

z

Z

MC results: calibration of misalignments

r=(3.7±0.2) x 10-3

z=(4.0±0.2) x 10-3

r=(3.9±0.2) x 10-3

z=(3.7±0.2) x 10-3

with use of 108 muons

K: 1 day collectionK: simultaneous data collection with K

PrPL

4 rotations

L:blackR: red

Target and tracking Better kinematical resolution Stronger K2 dif + BG

suppression

Addition of C0 and C1 GEM chambers with - high position resolution

- higher rate performance

Larger C3-C4 distance

Use of He bags

New target

E246 J-PARC

MC studies of tracking

Four chamber tracking including C0 with 0.1mm resolution Suppression of K2-dif down to ~1.0% Remaining BG is from the + decay between the target and C0. Further suppression down to 0.1% level with the fit trajectory consistency with target fibers, and tar

get fiber analysis.

PT (2 BG) < 10-4

K3 K2-dif

Beamline for K+ extraction

Momentum 800 MeV/cMomentum bite ±2.5%Acceptance 6.5 msr % p/pK+ intensity 3 ×106 /sK/ ratio > 2Beam spot 1.04 ×0.78 cm (FWQM)Final focus achromatic

K0.8 ( K1.1-BR)

K0.8

proton

Sensitivity estimate

Source PT • Net run time 1.0 ×107 s• Proton beam intensity 9A on T1• K+ beam intensity 3×106 /s• Total number of good K3 2.4×109

• Total number of fwd/bwd (N) 7.2×108

• Sensitivity coefficient 3.73√N

Total ~ 10-4

Statistical sensitivity Systematic errors Source PT z < 10-

4

z < 10-4

e+, Ee+ < 10-4

Total ~ 10-4

JPARC

SummaryPT in K3 is a very sensitive probe of new physicsWe propose a J-PARC experiment in the early stag

e of Phase 1 to pursue a limit of PT ~ 10-4.

New K0.8 beamlineUpgraded E246 detector

Stage 1 approval– Upgrade will be finished by 2010. – Data taking will be started from 2011.

Collaboration (present group)

Canada U.Saskatchewan TRIUMF UBC U. Montreal

USA MIT U. South Carolina Iowa State U.

Japan KEK Tohoku U. Osaka U. NDA

Beamline Target

Muon field magnet Active polarimeter CsI(Tl) readout DAQ

GEM chambers Tracking upgrade

We will organize more people after obtaining an approval.