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T violation in K decays using stopped K+
J. ImazatoIPNS, KEK
NP04 workshopAugust 3, 2004 Tokai
Transverse muon polarizationKEK E246 experimentJ-PARC experiment
E246 upgrade?LOI-19
Transverse muon polarization in K+→π0µ+ν
= very small
Kµ3 decay form factors and
T violation
History of Kµ3 transverse polarization experiments
• KL→π-µ+ν Bevatron 1967 Imξ = -0.02 ±0.08• KL→π-µ+ν Argonne 1973 Imξ = -0.085 ±0.064• KL→π-µ+ν BNL-AGS 1980 Imξ = 0.009 ±0.030• K+→π0µ+ν BNL-AGS 1983 Imξ = -0.016 ±0.025
Feature of K+µ3 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 contributionEfrosinin et al. PL B493 (2000) 293PT ~ 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
s i j u
W
K µ
π
ν
γ++
0
ππ K µ
π
ν
γ++
0
γ
SM
FSI (example)
Three Higgs doublet model
s µ s µ
u ν u ν
W H+ α γ
Higgs doublet model
L = (2√(2)GF)1/2 Σ[αiULKMDDR + βiURMUKDL + γiNLMEER] Hi+ + h.c.
flavor conservation
Imξ = Im(α1γ1*) x (mK / mH+)2
= Im(α1β1*) x (v2 /v3)2 x (mK / mH+)2
vi : vacuum expectation valuesαi, βi, γi : mixing matrix elements
s µ s µ
u ν u ν
W H+ α γ
0 2 0 4
0 6
0 8
0 1
0
0
1 0-
2
1 0-
1
1
1 0
1 02
Im(α
1β1* )
v2 / v3
mH = mZ × 2
KEK-E246 Imξ < 7 × 10−3
n-EDM
b → sγ
b → τνX
Kµ3 previous
Only schematic
Kµ3 PT
3HDM : constraints from other experiments
Neutron EDM (charged Higgs exchange)dn=Cn Im(α1β1*) < 0.63 x 10-25 e cm Im(α1β1*) < ~10
b→sγA = ASM + A3HDM(α1β1*) Im(α1β1*) ≦ 3.2 (for mH~2mZ)
[Grossman and Nir (1993), Kiers et al.(2000)]
ε /ε = (α1β1∗)) : but stringent constraintb→XτνA = ASM + A3HDM(α1γ1*)Im(αiγi*)=Im(α1β1*) (v2 /v3 )2 < 0.48 (for mH~2mZ)
[Grossman, Haber and Nir (1995)]
c.f. PT : Im(α1β1*) (v2 /v3 )2 < Imξ / 0.10
For v2 /v3 > ~ 10, PT is the most stringent constraint on 3HDM[Garisto and kane (1991)]
Other modelsSUSY + squark mixing
Su
µ ν
H+
bL~
g~tR~ PT
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M. Fabbrichesi and F. Vissani, Phys. Rev. D55 (1997) 5334
Guo-Hon Wu and John N. Ng, Phys. Rev. D56 (1997) 93 Charged Higgs exchangeConstraints onMH+
Λ=tanβ (µ+Atcotβ)/mg~x Im[V33
H+* V32DL * V31
UR]
slepton exchange +down-type squark exchangeConstraints onMH+
Im[λ2i2(λ’i12)*] and Im[λ’21k(λ’22k)*]
scalar leptoquark exchangeConstraints onλk
2/Mφk2
PT (K+→µ+νγ )no SM contribution, but induced by pseudoscalarcomplementary to PT (K→ πµν ) [Kobayashi et al. (1996)]FSI is not large : O(10-4 ) [Efrosinin and Kudenko (1999), Hiller and Isidori (1999)]
Model K+ → π0µ+ν K+ → µ+νγ
Standard Model <10-7 <10-7
Final State Interactions <10-5 <10-3
Multi-Higgs ≤ 10-2 ≤ 10-2
PT(K+ → π0µ+ν) ≈ 2 PT(K+ → π0µ+γ)
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)
E246 experimental setup[J.Macdonald et al.; NIM A506 (2003) 60]
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PT
µ+
π0BWD
PT
µ+
π0FWD
0 0.5 1.0 m
π0
f
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r
w
a
r
d
π0
b
a
c
k
w
a
r
d
A = NCW - NCCW
NCW + NCCW COILGAP
IRON POLE
µ+ STOPPER
e+ COUNTER
TARGET
CsI(Tl)
End view Side view
K+→π0µ+ν
r
Double ratio measurement
: analyzing power
π0
0-forward
PT
π0
0-backward
PT
PT directions
fwd -π0 (γ )bwd -π0 (γ )
Double ratio measurement
Afwd - AbwdAT =2
Muon holes
K+ CsI crystals
1010
556
67
7
8
44
32
1
2
9
1
3
8
9
4
CsI barrel
768 CsI barrel
K + Target
π (γ )π (γ )0
θπ (γ )π (γ )0
µ+
fwdfwdbwdbwdπ (γ )π (γ )0
fwd and bwd π0 /γ
E246 result and model implication
-0.2
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
0.2
1960 1980 2000
Year
Im(ξ)
BevatronArgonne
BNL
BNL KEKKEK
PT = - 0.0017 ± 0.0023(stat) ± 0.0011(syst)( |PT | < 0.0050 : 90% C.L. )
Imξ = - 0.0053 ± 0.0071(stat) ± 0.0036(syst)( |Imξ | <0.016 : 90% C.L. )
Three Higgs doublet model
|Imξ | < 0.016 (90% C.L.) ⇒ Im(α1γ1*) < 544 (at mH=mZ)
cf. BR (B→Xτντ) ⇒ Im(α1γ1*) < 1900 (at mH=mZ)
[R.Garisto and G.Kane, Phys. Rev. D44 (1991)2789] v2/v3 = mt /mτdn ≈ 4/3 dd ∝ Im(α1β1
*) × md / mH2
|Imξ | < 0.016 (90% C.L.) ⇒ dn < 5 ×10-27 e cmcf. dn
exp < 6.3×10-26 e cm
Systematic errorsΣ12 : 12-fold rotational cancellationfwd/bwd : π0 forward/backward cancellation
Source of Error Σ12 fwd/bwd δPT 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 <0.1µ+ counter f-offset x o <0.1MWPC φ-offset (C4) x o 2.0CsI misalignment o o 1.6B offset (ε) x o 3.0B rotation (δx) x o 0.4B rotation (δz) x x 5.3K+ stopping distribution o o <3.0µ+ multiple scattering x x 7.1Decay plane rotation (θr) x o 1.2Decay plane rotation (θz) x x 0.7Kπ2 DIF background x o 0.6K+ DIF background o x < 1.9Analysis - - 3.8
Total 11.4
E246 upgrade at J-PARC?E246 was statistically limitted.
Polarimeter field by a new magnet Parallel holding field of PT Precise field distribution alignment
reduction of the most serious systematic errorActive polarimeter
4π solid angle for decay positron Energy and angle of positrons
FoM = α√Ω = 3.8 x E246Time digitizer readout of CsI(Tl)
Rate performance = 10 x E246under the condition of K/π >>1
MeritLower cost than a completely new setupWell known detector performance and systematicsMany possibilities for kaon decay spectroscopy
E246 muon polarimeter
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µ+ →
e+νeνµ
Sµ
e + e +
Nc
w
N c c
w
=
1
+
AT
AT
=
αPT
-10 -5 0 5 10 y (cm)
µ stopper Trigger counter
Cu degrager
TOF counter
C4 chamber
Left e counters Right e counters+ +
Fe field trim
µ+
e++
B
One-sector viewCross section
y(cm)
New polarimeter system
-10 -5 0 5 10 y (cm)
activepolarimeter
C4 chamber
µ+
activepolarimeter
BMagnet Magnet
Coil
B~ 300 Gauss
Expectation for E246-upgrade
Gain from E246Polarimeter : 3.8Beam intensity : √10Run time : √0.66Total = 9.8
Statistical error : δPT = 3.0 x 10-4
Systematic errors
Total error : δPTsyst ~ 10-4
J-PARC proposal LoI-19
Experiment principle• stopped kaons• double ratio• detector azimuthal symmetry • complete reconstruction of kinematics Detector concept• larger µ+ acceptance• high resolution π0 measurement• active polarimeter• photon veto Most important requirement• suppression of systematic errors to the 10-4 level
Original design
“PT in K+→π0µ+ν and K+→µ+νγwith δPT <10-4 and δPT ~10-4 ”
A new detector with• improved charged particle acceptance• a high resolution photon detection
)1)(cos1(
222
20
0 X
mE
−−=
ηππ
21
21EEEEX +
−=
22 )()()( 000ηπ
γππ
EErmsE ∆+∆=∆
ηπηπ βσγ 25.0 mE =∆
angular contribution = small for X -> 0
Further optimization are necessary taking into acount ;
Detector acceptanceSystematic errorsEvent selection performance
Vector correlation
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C
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l
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Cryostat
At J-PARCHigher beam rateDifferent conditions forup- and down-stream side
Double ratio betweenleft -going π0 andright-going π0
Beam
µ µ
π
π
PTPT
E246 experiment J-PARC experiment
Symmetrization of K+ stopping distribution
K
µ
polarimeter
target
tracker
+
+
z
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
butunknown higher order systematics
Artificial z- symmetrization by using tracker===> A0 = 0
Adjustment of null asymmetry
A0= ( Aleft + Aright)/2
Necessity of magnetic field
P (fwd)
P (bwd) δP
δP
δBrθ
θ = δω x τδP = θ x P
T
TN
N
NT
Zero field experimentnecessary condition= δBr < 1 m Gauss very difficult to make
+∝
+
Calorimeter
Preshower detectors
Degrader
Active targetK
Central tracker
Veto counters
Trackers
γ
γ
γ
Polarimeter
-veto and calorimeter
solenoid coil
0 0.5 1.0 m
Large solenoid
Field paremetersStrength : 1-3 kGAlignment+symmetry : 10-4
100 µ over 1mField measurement with arotating coils
Allowed stray field : 100 mG
Use of the field for tracking
Effects of magnetic field on polarization
B
PP
P
Lleft
right
PLP
P
left
rightδ
δP = P x sin δLT
Cancellation between +δ and -δNull asymmetry checkCancellation between left and right
Same situation as in the zero field case
Rejection of Kπ2 background
µ+
π0 π0
π πµ µ
φ =11゜max φ =11゜max
ϕ = 40゜max
γ (Eγ > 100 MeV)
two γ one γ
++ + +
θµπ< 79o θµγ < 39o
Optimization of Kπ2 background rejection byOpening angle cuts, andX-parameter cut
Active polarimeter
Problem of use of plastics• formation of muonium• muon spin depolarization
AnalysisMichel spectrum
k k
Measurement ofMuon stopping positionPositron emission directionPositron energyElectromagnetic shower
location energy deposit
B=3kG enough for decoupling?
Better choice will bemuon tubes made of Al
Instrumental systematicsMisalignments
⦿ ⦿
×× ××
⦿⦿⦿⦿
B
B
P
P
left
left
δP
δP
T
T
n
n
CsI
CsI
p π
p π
µp
pµp x pπ
πp x p
µ
µ
TOPTOP
Bottom Bottom
(a) (b)
π0 calorimeter
spurious δPT decay plane rotation
Magnet
Cancellation by azimuthal integration
Photon veto and Kµνγ
Identification of one γ eventsRejection of π0 -> 2γ events
∝+
K+
Trackers
γ
γDegrader
γ veto and calorimeter
Polarimeter
×Ο
µ+
γ
PT = σµ · (pµ × pγ )
µ stopper &Active polarimeter+ γ veto function
γ veto
µpµ= 100~210 MeV/c
~10X0
50g/cm2
~2X0
γBoth µ and γ in the polarimeter
Rough estimate of Kµνγ PT
1. Photon energy 20 – 200 MeV2. Muon energy ≥ 200 MeV3. θγµ ≤ 120O
Acceptance per K+ ∼ 0.7 x 10-4
N(K+ → µ+νγ) ∼ 0.7 x 1010
Statistical sensitivity ∆PT(1σ) ∼ 0.7 x 10-4
(estimate based on fwd/bwd scheme)
High rate performancej
Detector elements are designed from now on.
R&D of pre-shower counter started at INR.
Each element will be highly segmented.
Target : fiber targetTracker: high rate chamber + Scifiγ−detector: pre-shower counter + fast crystal or
fiber sampling shower counterγ-veto : highly segmented
Polarimeter: highly segmented.
Kaon beam
K0.8 at T1 targetIn Phase 1 for stopped K+/- beam
T2 target in Phase2
p= 650~800 MeV/cK/π > 1 with two DCSs∆p/p < 3%K+ intensity =106 ~ 107 /s
Is it possible to use the K1.1 line?C-type branch of K1.1
• how to optimize beam optics?• how to put two DCS? • how to coexist with the future High-p line?
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