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T violation search in K decays using stopped K+
J. ImazatoIPNS, KEK
Workshop on Physics at an Upgraded FermilabProton Driver Workshop
October 8, 2004
1. Transverse muon polarization in K+
2. KEK E246 experiment3. Future experiments4. J-PARC experiment
Transverse muon polarization in K+→0+
K3 decay form factors and T violation
History of K3 transverse polarization experiments
• KL→−+ Bevatron 1967 Im = -0.02 ±0.08• KL→−+ Argonne 1973 Im = -0.085 ±0.064• KL→−+ BNL-AGS 1980 Im = 0.009 ±0.030• K+→0+ BNL-AGS 1983 Im = -0.016 ±0.025• K+→0+KEK-E246 2004 Im = -0.0053 ±0.0071 ±0.0036
PTspurious(Final State Interaction)= very small
T-odd correlation
Features of K+ PT
■ Small standard model contribution
– Bigi and Sanda “CP violation” (2000)– PT ~ 10-7
■ Small FSI spurious effects– Single photon contribution Zhitnitskii (1980) PT < ~ 10-6
– Two photon contribution Efrosinin et al. PL B493 (2000) 293 PT ~ 4 x 10-6
■ High sensitivity to CP violation beyond the SM
– Mult- Higgs doublet model– Leptoquark model– Some Supersymmetric models PT ~ 10- 4-10- 3
Three Higgs doublet model
SM
FSI (example)
Higgs doublet model
L = (2√(2)GF)1/2 [iULKMDDR + iURMUKDL + iNLMEER] Hi+ + h.c.
flavor conservation
Im = Im(11*) × (mK / mH+)2
= Im(11*) × (v2 /v3)2 × (mK / mH+)2
vi : vacuum expectation valuesi, i, i : mixing matrix elements
Only schematic
K PT
v2 /v3
Im(
11* )
Im(*) (v2 /v3 )2 / MH2 = 4.1×ImGeV-2
3HDM : constraints from other experiments
Neutron EDM (charged Higgs exchange)dn=Cn Im(11*) < 0.63 x 10-25 e cm ⇨ Im(11*) < ~10
b→sA = ASM + A3HDM(*) ⇨ Im(*) ≦ 3.2 (for mH ~2mZ)
[Grossman and Nir (1993), Kiers et al.(2000)]
but stringent constraint b→X
A = ASM + A3HDM(*)Im(ii*)=Im(*) (v2 /v3 )2 < 7400 (for mH ~2mZ)
[Grossman, Haber and Nir (1995)]
c.f. PT : Im(*) (v2 /v3 )2 = 1.36 ×105 Im(for mH ~2mZ) For v2 /v3 > ~ 10, PT is the most stringent constraint on 3HDM [Garisto and kane (1991)]
Other models
Charged Higgs exchangeConstraints onMH+
=tan(+Atcot)/mg~
× Im[V33H+* V32
DL * V31UR]
slepton exchange +down-type squark exchangeConstraints onMIm[2i2(’i12)*] and Im[’21k(’22k)*]
scalar leptoquark exchangeConstraints on k
2/Mk2
R- parity violating SUSY
W = WMSSM + WRPV __ __ __ __ __
WRPV =ijkLiLjEk + ’ijkLiQjDk + ”IjkUiDjDk
Li, Qi : lepton and quark doublet superfield
Ei, Di , Ui : electron, down- and up-quark singlet superfield
Constraint from Im on Im[2i2(’i12)*]/M2 and Im[’21k(’22k)*]/M2
Constraint on from ImE246) Im[2i2(’i12)*] and Im[’21k(’22k)*] ×@ M=100 GeVwhile constraint from other experiments : ≤ 4 × 10-2 @ M=100 GeV
PT (K+→no SM contribution, but induced by pseudoscalar interactionscomplementary to PT (K→ [Kobayashi et al. (1996)]FSI is not large : O(10-4 ) [Efrosinin and Kudenko (1999), Hiller and Isidori (1999)]
Model K+ 0+ K+ +
■ Standard Model <10-7 <10-7
■ Final State Interactions <10-5 <10-3
■ Multi-Higgs 10-2 10-2
PT(K+ 0+) 2 PT(K+ 0+)
■ SUSY with sqarks mixing 10-3 3x10-3
■ SUSY with R-parity breaking 4x10-4 3x10-4
■ Leptoquarks 10-2 5x10-3
E246 : PT = -0.0064 ± 0.0185 (stat) ± 0.0010 (syst) Phys. Letters B561, 166 (2003)
PT = -0.0067 ± 0.0143 (stat) ± 0.0014 (syst)
KEK E246 experiment
Japan ● KEK ● Univ. of Tsukuba, ● Tokyo Institute of Technology
● Univ. of Tokyo ● Osaka Univ.Russia ● Institute for Nuclear ResearchCanada ● TRIUMF ● Univ. of British Columbia
● Univ. of Saskatchewan ● Univ. of MontrealKorea ● Yonsei Univ. ● Korea Univ.U.S.A. ● Virginia Polytech Institute ● Princeton Univ.Taiwan ● National Taiwan Univ.
E246 experimental setup using stopped K+
End view Side view
[J.Macdonald et al.; NIM A506 (2003) 60]
K+→0+
E246 muon polarimeter
Cross section One-sector view
y(cm)
B
Double ratio measurement
CsI barrel fwd and bwd 0 /
PT directions
fwd -bwd -
Double ratio measurement
768
Afwd - AbwdAT = 2
E246 result and model implication
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. )
[M.Abe et al., Phys. Rev. Letters 93 (2004) 131601]
Three Higgs doublet model
|Im| < 0.016 (90% C.L.) ⇒ Im(11*) < 2176 (at mH=
2mZ) cf. BR (B→X) ⇒ Im(11
*) < 7400 (at mH=2mZ)
[R.Garisto and G.Kane, Phys. Rev. D44 (1991)2789] v2/v3 = mt /m
dn ~ 4/3 dd ∝ Im(11*) × md / mH
2
|Im| < 0.016 (90% C.L.) ⇒ dn < 5 ×10-27 e cm cf. dn
exp < 6.3×10-26 e cm
KL
K+
Systematic errors
Source of Error 12 fwd/bwd PT x 104
e+ counter r-rotation x o 0.5e+ counter z-rotation x o 0.2e+ counter f-offset x o 2.8e+ counter r-offset o o <0.1e+ counter z-offset o o <0.1+ counter f-offset x o <0.1MWPC-offset (C4) x o 2.0CsI misalignment o o 1.6B offset () x o 3.0B rotation (x) x o 0.4B rotation (z) x x 5.3K+ stopping distribution o o <3.0+ multiple scattering x x 7.1Decay plane rotation (r) x o 1.2Decay plane rotation (z) x x 0.7K2 DIF background x o 0.6K+ DIF background o x < 1.9Analysis - - 3.8
Total 11.4
12 : 12-fold rotational cancellation fwd/bwd : 0 forward/backward cancellation
Stopped K+ vs. in-flight decay method stopped K+ method in-flight-decay method
Example E246 old BNL experiment
K+ beam momentum low p for stopping high p K+ beam intensity low high
Decay kinematics isotropic boosted forward
0 detection all directions only forward decay?
Sensitive regionto PT possible not always
Kinematic resolution good poor
Double ratio exp. possible difficult
+ polarization measurement for K3 PT Method longitudinal field transverse field
• Configuration
• Observable• Experiment E246 old BNL experiment• Relative sensitivity 1 1/√2
• Systematic error double ratio B field reverse reduction AT, -AT t+T, -t+T
• Matching with stopped K+ good good
• Systematic error small ● error due to B reverse ● t0 calibration necessary
Future T violation experiment and sensitivity limitations
■ Methodology : Stopped K+ method rather than an in-flight decay experiment Double ratio measurement in the decay kinematic space Longitudinal field on the PT component
■ Desirable detector : Large K3 acceptance Simultaneous K PT measurement Small instrumental systematic errors
■ Sensitivity goal : E246 : PT
stat(E246) > PTsyst(E246)
Future experiment (FE) : PT
syst(FE) ~ 1/10 PTsyst(E246) ~ 10-4
PT
stat(FE) ~ PTsyst(FE) ~ 10-4
PTsyst(FE) ~ 10-4 might be feasible, but PT
syst(FE) ~ 10-5 will be vey difficult.
E246 upgrade at J-PARC ?
E246 was statistically limited.■ Polarimeter field by a new magnet Parallel holding field of PT Precise field distribution alignment
reduction of the most serious systematic error
■ Active polarimeter 4 solid angle for decay positron Energy and angle of measurements of positrons
FoM = √ = 3.8 x E246■ Upgrade of readout electronics
Rate performance = 10 x E246 under the condition of K/ >>1
Merit Lower cost than a completely new setup Well known detector performance and systematics
Expectation for E246-upgrade
Gain from E246 Polarimeter : 3.8 Beam intensity : √10 Run time : √0.66 Total = 9.8 Statistical error : PT = 3.0 x 10-4
Systematic errors
Total errorPT syst ~ 10-4
New detector proposal at J-PARC
To go down below 10-4, we need a new detector.
■ Experiment principle•stopped kaons•double ratio•detector azimuthal symmetry •complete reconstruction of kinematics
■ Detector concept•larger + acceptance •high resolution 0 measurement•active polarimeter•photon veto to measure K
■ Most important requirement•suppression of systematic errors to the 10-4 level
J-PARC proposal L-19
Large solenoid■ Field parameters Strength : 1-3 kG Alignment+symmetry : 10-4
100 over 1m Field measurement with a rotating coils
Allowed stray field : 100 mG
Use of the field for + and e+ tracking
K+ --> : PT <10-4 K+--> : PT ~10-4
■ Detector components Target calorimeter Pre-shower counter + tracker Polarimeter veto counters Large solenoid
Vector correlation
At J-PARC Higher beam rate Different conditions for up- and down-stream side
Double ratio between left -going 0 and right-going 0
Symmetrization of K+ stopping distribution
z
■ Adjustment of null asymmetry
A0= ( Aleft + Aright)/2
N(zK)=symmetric => A0= 0 N(zK)=asymmetric=> A0≠0
■ AT= ( Aleft - Aright)/2No effect in AT from asymmetric z-distribution due to left-right cancellation but unknown higher order systematics
Artificial z- symmetrization by using tracker ===> A0 = 0
0- L/R scheme ==> e+- F/B asymmetry measurement
Effects of magnetic field on polarization
Cancellation between + and - Null asymmetry check Cancellation between left and right
Presence of B field has no influence on the validity of experiment Same situation as in the zero field case
z=0
Active polarimeter
■ Measurement of Muon stopping position Positron emission direction Positron energy Electromagnetic shower
■ location■ energy deposit
■ AnalysisMichel spectrum
■ Problem of use of plastics• formation of muonium• muon spin depolarization
B=3kG enough for decoupling?
Better choice will bemuon tubes made of Al
k k
a system with the highest sensitivity to polarization
Rejection of K2 background
+
< 79o < 39o
Optimization of K2 background rejection by Opening angle cuts, and X-parameter cut on photon spectrum X= (E1-E2)/ (E1+E2)
K2 was a significant background in E246..
Instrumental systematics Most dangerous systematics will be instrumental misalignments
magnet calorimeter
Cancellation by azimuthal integration
spurious PT decay plane rotation
Sensitivity forKPT
•FoM = √•Run time 1 = 107 s•Loi-19 estimate based on fwd/bwd scheme
_
10-5 10-5
Estimate of K PT sensitivity
1. Photon energy 20 – 200 MeV2. Muon energy 200 MeV3. 120O
Acceptance per K+ 0.7 x 10-4 N(K+ +) 0.7 x 1010
Statistical sensitivity : PT(1) 0.7 x 10-4
(estimate based on F/B scheme)
Kaon beam
K0.8 at T1 targetIn Phase 1 for stopped K+/- beam
T2 target in Phase2
p= 650~800 MeV/c K/ > 1 with two DCS’sp/p < 3% K+ intensity =106 ~ 107 /s low p kaon line
K+ beam for stopped K+ experiments
K+stop = Ip K+(Ep) C T(pK) stop(pK)
Ip : proton beam intensity K+(Ep) : K+ production rate at Ep ↑with Ep
C : channel acceptance T(pK) : channel transmission ↑with pK
stop(pK): stopping efficiency ↓with pK
K+/+ ratio ↓with pK
Optimum pK @ Ep=12 GeV (E246) : 650 MeV/c with one DCS @ Ep= 30-50 GeV (J-PARC) : 650~800 MeV/c longer channel with two DCS’s
K+(Ep) : nearly constant with Ep in the relevant Ep region for pK= 650~800 MeV/c
consideration on optimum beam momentum
Summary
■ Transverse muon polarization PT is a clean and very sensitive probe of new physics.
■ KEK-E246 has recently improved the limit of PT and Im.
■ Future experiments aiming for PT ~10-4 will be important and desired.
■ The experiment at J-PARC using a stopped beam will be very promising:
K+ 0+ PT <10-4 K+ + PT ~ 10-4