1. 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

2. 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)

3. 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 = ± (stat) ± (syst)
( |PT | < : 90% C.L. ) PRD73, 72005(2006)

4. 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

5. 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 = ± (stat) ± (syst)
Imx = ± (stat) ± (syst)

6. 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 ≤ 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

7. 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

8. 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 rAl
m+ stop efficiency ~ 95%
Small systematics for L/R positron

9. 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

10. Beamline for K+ extraction
K0.8 ( K1.1-BR)
proton
Final Focus
Momentum MeV/c
Momentum bite ±2.5%
Acceptance msr % Dp/p
K+ intensity ×106 /s
K/p ratio > 2
Beam spot ×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

11. 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

12. Cancellation mechanism for misalignmentsq0
: 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

13. Sensitivity estimate of TREK
Statistical sensitivity
Systematic errors
Source dPT
Net run time ×107 s　
-- one year run
Proton beam intensity mA on T1
K+ beam intensity ×106 /s
-- 30 times of E246
Total number of good Km ×109
-- detector acceptance: 8 times of E246
Total number of fwd/bwd (N) 7.2×108
Sensitivity coefficient √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

14. 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

15. backup

17. 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 = ± (stat) ± (syst)
( |PT | < : 90% C.L. )
Imx = ± (stat) ± (syst)
( |Imx | <0.016 : 90% C.L. )
PRD73, (2006)
Statistical error dominant

18. 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