Transcript Result of T-violating Muon Polarization Measurement in the K+→p0m+n Decay J. Imazato IPNS, KEK for the KEK-E246 collaboration March 21, 2004 XXXIXth Rencontres de Moriond Transverse muon.

Result of
T-violating Muon Polarization Measurement
in the K+→p0m+n Decay
J. Imazato
IPNS, KEK
for the KEK-E246 collaboration
March 21, 2004 XXXIXth Rencontres de Moriond
Transverse muon polarization
 E246 experiment
 Analysis
 Result of the total data

E246 collaboration
Japan
Russia
Canada
Korea
U.S.A.
Taiwan
KEK ● Univ. of Tsukuba,
● Tokyo Institute of Technology
● Univ. of Tokyo ● Osaka Univ.
● Institute for Nuclear Research
● TRIUMF ● Univ. of British Columbia
● Univ. of Saskatchewan ● Univ. of Montreal
● Yonsei Univ. ● Korea Univ.
● Virginia Polytech Institute ● Princeton Univ.
● National Taiwan Univ.
●
Transverse Muon Polarization in K+→p0m+n
Km3 decay form factors and
T violation
History of Km3 transverse polarization experiments
• KL→p−m+n
• KL→p−m+n
• KL→p−m+n
• K+→p0m+n
Bevatron 1967
Argonne 1973
BNL-AGS 1980
BNL-AGS 1983
Imx = -0.02 ±0.08
Imx = -0.085 ±0.064
Imx = 0.009 ±0.030
Imx = -0.016 ±0.025
Feature of K+m3 PT
■
Small standard model contribution
–
–
■
SM
Bigi and Sanda “CP violation” (2000)
PT ~ 10-7
Small FSI spurious effects
– Single photon contribution
FSI (example)
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
KEK E246 experiment
Features
■
■
Stopped K+ experiment with a SC toroidal spectrometer
Measurement of all decay kinematics directions
– Double ratio measurement with small systematic errors
History
■
1992-1995 : detector construction
■
1996-2000 : data taking
■
1999
: first result published with 1/4 of data
Imx = -0.023 ± 0.007(stat) ± 0.003(syst)
[M.Abe et al., Phys.Rev.Lett. 83(1999) 4253]
■
■
2001-2003 : analysis
2004 (this conference) : report of the final result
Byproducts
■
■
K+→m+ng : PT = -0.0064 ± 0.0185(stat) ± 0.0010(syst)
Ke3, Kp2g, Ke4, ...
[V.Anisimovsky et al., Phys.Lett. B562 (2003) 166]
Superconducting toroidal magnet
E246 experimental setup
[J.Macdonald et al.; NIM A506 (2003) 60]
End view
Side view
K+→p0m+n
E246 detector
Muon polarimeter
One-sector view
Cross section
y(cm)
CsI(Tl) and kinematics
CsI barrel
fwd and bwd p0 /g
PT directions
fwd -p0 (g )
bwd -p0 (g )
Double ratio measurement
Experimental data
K+m3 event selection
e+ time spectrum
TOF analysis
e+ time spectra
CsI(Tl) analysis : 2g
Momentum
analysis
Analysis
Km3 event selection
fwd events : cosqp0(g) > 0.341
bwd events : cosqp0(g) < -0.341
e+ time spectrum anlysis
Ncw(ccw) : integration from 20ns to 6 ms
with constant BG subtracted
Asymmetry analysis

AT (y)=[A(y)fwd - A(y)bwd] /2
A(y)f (b) =

• =2g; o=1g
[Ncw(y)-Nccw(y)]f(b)
[Ncw(y)+Nccw(y)]f(b)
PT (y) =AT (y) / a(y) <cosqT>
a(y) = AN(y) / PN
⇒
∫

PT = PT (y) w (y)dy

Imx = PT / <PT/Imx>
Two independent analyses
■
Two analyses by two teams with
 their own analysis policy and
 event selection methods
Comparison of good Km3 event e.g. :1998
2g events
1g events
A2
A1
1221 k
918 k
1264 k
909 k
of the two analyses
by resorting of events to 6 data sets
2g
—
A1•A2 A1• A2
—
A1• A2
1g
■Combination
—
A1•A2 A1• A2
—
A1• A2
Merits of two analysis method
Cross check of data quality by A0, decay plane rotation qr and qz and PT
 Comparison of sensitivity by normal asymmetry AN and <cosqT>
 Check of data quality in e.g. A1 by comparing A1•A2 and A1• A2-bar
 Estimate of systematic error by comparing <cosqT> of A1• A 2 from A1 and
 Improvement of statistical error

A2
Data quality check
Null asymmetry check
A0=[(Ncw/Nccw)total -1]/2
total = fwd + bwd
Sensitivity check
AN=(Aleft - Aright)/2
Aleft = [(Ncw/Nccw)left -1]/2
Aright= [(Ncw/Nccw ) right -1]/2
• 6 data sets for each period
• Open circles are 2g events and dots are 1g events.
 Null asymmetry is canceled by double ratio (fwd-bwd).
Result
PT = - 0.0018 ± 0.0023(stat) ± 0.0011(syst)
( |PT | < 0.0051 : 90% C.L. )
Imx = - 0.0055 ± 0.0073(stat) ± 0.0036(syst)
( |Imx | <0.016 : 90% C.L. )
Systematics check
Consistency among data
Sector dependence
●
●=1996-1997;
= 2g ; o =1g;
o=1998; ★=1999-2000
Decay plane rotation
Imx = -0.0055±0.0073
(c2/d.o.f = 0.78)
|qr(fwd)- qr(bwd) | ≤ 4.6×10-4 rad
|qz(fwd)- qz(bwd) | ≤ 2.6×10-4 rad
Systematic errors


S12 : 12-fold rotational cancellation
fwd/bwd : p0 forward/backward cancellation
Source of Error
e+ counter r-rotation
e+ counter z-rotation
e+ counter f-offset
e+ counter r-offset
e+ counter z-offset
m+ counter f-offset
MWPC f-offset (C4)
CsI misalignment
B offset (e)
B rotation (dx)
B rotation (dz)
K+ stopping distribution
m+ multiple scattering
Decay plane rotation (qr)
Decay plane rotation (qz)
Kp2 DIF background
K+ DIF background
Analysis
Total
S12
fwd/bwd
x
x
x
o
o
x
x
o
x
x
x
o
x
x
x
x
o
-
o
o
o
o
o
o
o
o
o
o
x
o
x
o
x
o
x
-
dPT x 104
0.5
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
38
11.4
Model implications
Three Higgs doublet model
L = (2√(2)GF)1/2 S[aiULKMDDR + biURMUKDL + giNLMEER] Hi+ + h.c.
Imx = Im(a1b1*) ×(v2 /v3)2 × (mK / mH+)2
= Im(a1g1*) × (mK / mH+)2
vi : vacuum expectation values
ai, bi, gi : mixing matrix elements
 |Imx | < 0.016 (90% C.L.) ⇒ Im(a1g1*) < 544 (at mH=mZ)
− ) ⇒ Im(a g *) < 1900 (at m =m )
cf. BR (B→Xtn
t
1 1
H
Z
Neutron EDM in 3HD model
dn ≈ 4/3 dd ∝ Im(a1b1*) × md / mH2
v2/v3 = mt/mt [R.Garisto and G.Kane, Phys. Rev. D44 (1991)2789 ]
 |Imx | < 0.016 (90% C.L.) ⇒ dn < 9 ×10-27 e cm
cf.
dnexp < 6.3×10-26 e cm
Summary
■
Transverse muon polarization in K+→p0m+n decay is a good probe of
CP violation beyond the standard model.
■
The final result of the KEK-E246 experiment showed no evidence for
T violation with Imx = - 0.0055 ± 0.0073(stat) ± 0.0036(syst) , or
|Imx | <0.016 (90% C.L. ).
■
This limit constrains the parameters of some non-standard CP violation
models with high sensitivity.
■
We are going to propose a next generation PT experiment at the high
intensity accelerator J-PARC.
Decay plane rotation
<qz>=
-0.004±0.12 mr
<qz>=
0.02±0.14 mr
<qr>=
0.27±0.48 mr
<qr>=
-0.20±0.58 mr
B field rotation
CsI(Tl) photon detector
Segmentation
Number of crystals
Length of crystals
Inner radius
Outer radius
Solid angle
Readout
Light yield
Equiv. noise level
Dq = Df = 7.5o
768
25 cm (13.5 X0)
20 cm
50 cm
~75%of 4p
PIN diode
11000 p.e./MeV
65 keV
[D.V.Dementyev et al. Nucl. Instr. Method A440 (2000) 151]
Double ratio measurement
Analysis: methodology
 Blind analysis
■
Event selection optimization before looking at AT
 Two independent analyses
■
■
■
Easy to find any trivial mistakes in data reduction and analysis codes
Competition with each other for better analysis codes
Minimize potential human bias in the analysis
 Combination of two results
■
■
■
Analysis of “common” and “uncommon” events to check the event quality
Makes it possible to estimate systematic error associated with analysis
Improves the statistical accuracy
1998 data: p0 mass spectrum
comparison with 1996-97