Transcript Measurement of T-violating Transverse Muon Polarization in

Sep. 1, 2007
JPARC TREK Collaboration meeting at Saskatchewan
Updated sensitivity estimate
(1) Statistical error
(2) Systematic error
Suguru Shimizu
Osaka University
 FOM∝AT√ N was calculated by
this formula (see FIFC and PAC
reports).
 Analyzing power is
α=0.38 (at FOM max.)
 e+ energy measurement is not
so important. Just accept high
energy e+ component.
 Best e+ angle threshold is
about 0.4
e+ energy (MeV)
Analyzing power and FOM
0.96
0.92
cosθ
y
e+
θ
beam
e+ angle cut is effective to improve FOM,
while e+ energy measurement is less important.
FOM for p0 angle threshold
for the p0 fwd/bwd analysis
π0
θ
Beam axis
FOM was determined as a function of
cos θπ (see FIFC and PAC reports).
<cos θT >=0.68 (at FOM max.)
cosθπ
Summary of FOM study
parameters: e+ energy, e+ angle, p0 angle
AT
PT＝
α<cosqT>
a
=0.38
<cosqT>=0.68
ΔPT=1.2x10-4 is obtained with 2.4G Km3 events under the
best FOM condition (only pi0 fwd/bwd analysis).
cosθπ
Systematic error from B field rotation
Side View
End View
B
PNfwd
spectrometer
PNfwd
m+
PNbwd
p0
fwd
p0
bwd
Left
PTfwd
Right
PTbwd
B
Left
Right
PNbwd
π0 fwd 1+ a PT
bwd 1- a PT
fwd/bwd = 1+2aPT
π0 fwd 1+ b PN
bwd 1- b PN
fwd/bwd = 1+2bPN ≠1
systematic error
1mrad. uncertainty of B field
D PT = 10-3
Calibration of the polarimeter
misalignment using experimental
data is very important.
Systematic error due to misalignments
Rot(dz) misalignment
Rot(dr) misalignment
beam
ideal B
ideal B
Asymmetry
Asymmetry
R comp.
beam
offset
Z comp.
Offset is generated from
R component of muon spin
R comp.
Z comp.
offset
Offset is generated from
Z component of muon spin
Systematic error due to misalignments
Rot(dr) misalignment
Rot(dz) misalignment
beam
ideal B
ideal B
Asymmetry
Asymmetry
R comp.
beam
offset
R comp.
Z comp.
Z comp.
Offset is generated from
R component of muon spin
offset
Offset is generated from
Z component of muon spin
Introduction of q0
(See E06 technical note No.2)
Time integrated e+ left/right asymmetry
- dz sinq0 + dr cosq0
Time integrated asymmetry
q0 : the muon spin phase at t=0
In general, e+ left/right asymmetry can be
described by oscillating terms and constant terms
(see E06 technote No.2)
Km3
Black: π0 fwd
Red : π0 bwd
q0 (deg)
q0 is determined
event by event.
Oscillation terms can be canceled out by the time integration.
Cancellation mechanism for misalignments
Characteristic θ0 dependence of PT and d.
Km3 MC, Non-zero PT
π0
Km3 MC, PT=0, δz=5deg
π0 bwd
bwd
π0
fwd
A(q0)fwd≠ A(q0)bwd
π0 fwd
A(q0)fwd= A(q0)bwd
= drcosq0-dzsinq0
Cancellation mechanism for misalignments
Characteristic θ0 dependence of PT and d.
Km3 MC, Non-zero PT
Km3 MC, PT=0, δz=5deg
Asum
Asum
Asub
Asub
Asub=(Afwd−Abwd)/2. ≠ 0
Asub = 0
Asum=(Afwd+Abwd)/2. = 0
Asum ≠ 0
d effect is drastically reduced by Asub .
Effect of misalignments are cancelled out by the θ0 analysis.
Separation of PT and misalignments effect
Black: no misalignment, non-zero PT
Blue: δz=5deg,
non-zero PT
Asub
Asub=(Afwd−Abwd)/2.
Asum
i/o
i/o
Asum=(Afwd+Abwd)/2.
δ
i/o : No misalignment
δ：δz=δr= 5 deg.
dPT (stat)= 1.3 x 10 -4
dPT (syst)< 10 -4
with 2.4G Km3 events
Misalignments are now harmless!
δ
Estimation of systematic error due to
misalignments
Misalignments:
Assumption in MC is
5 degree
Misalignments:
Real case is ~mrad.
If dPTsys~10-4 in real case,
dPTsys= (2±7)x10-4 was
obtained in MC
In case of 5 degree,
dPTsys should
= be 10-4 x 5deg. /mrad
~ 10-2
compare
The systematic error is expected to be much smaller than 10-4 .
Summary of p0 fwd/bwd analysis
• Sensitivity of p0 fwd/bwd analysis:
statistical error
1.2x10-4
systematic error <1.0x10-4
in total
1.2x10-4
To improve the sensitivity
(1) p0 left/right analysis
(2) Can we use high energy 1g detection with veto counter
hit events?
PT determination for p0 left/right events
 p0 left/right analysis
PL component are also rotated, together with PT.
 PL component can be removed by comparing p0 left and right events.
Beat pattern due to
the finite PT can be observed.
p0 left/right analysis
 Asub=(Aleft-Aright)/2 is calculated before time integration of m decay time.
 Large PL component can be removed by this subtraction.
Km3 MC, Non-zero PT
e+ asymmetry
Black:
Red:
p0 left
p0 right
Large PL component is seen.
Asub=(Aleft-Aright)/2
PT component can be extracted.
p0 left/right analysis
• Asub=(Aleft−Aright)/2 is fitted with,
a cos(wt+f+b)
a, f : fitting parameter
b: 0
for e+ fwd/bwd analysis
p/2
for e+ in/out analysis
e+
e+ detection
fwd
R
e+ fwd/bwd
e+ in/out
black:
red:
a
out
bwd
in
Z
f
dPT = 1.7 x 10 -4 for 2.4G Km3 events
Asub=(Aleft−Aright)/2.
e+ asymmetry
bwd-fwd
bwd+fwd
e+ asymmetry
in-out
in+out