Transcript Measurement of T-violating Transverse Muon Polarization in

Sep. 1, 2007
JPARC TREK Collaboration meeting at Saskatchewan
Active polarimeter simulation
Suguru Shimizu
Osaka University
Assembly of Active polarimeter
Identification of muon stopping point/ decay vertex
 Measurement of positron energy Ee+ and angle qe+
 Large positron acceptance of nearly 4p
 Higher sensitivity
Parallel plate stopper with
 Lower BG in positron spectra
Gap MWPC

Number of plates
Plate material
Plate thickness
Plate gap
Ave. density
m+ stop efficiency
31
Al, Mg or alloy
~ 2 mm
~ 8 mm
0.24 rAl
~ 85%
Small systematics for L/R positron
 Fit for p0 fwd/bwd measurement

Plates are ground potential
Muon stopping distribution
in the stopper
r= 0.2rAl
= 0.54 g/cm3
t/d = const.
d=2 mm
d=8 mm
estop > 85%
d (mm)
d = 8 mm
t=2 mm
t = 0. 5 mm
r (g/cm3)
Stopping prob. is determined by effective density.
for
t = 2 mm
d =8 mm
Readout assembly for gap MWPC
• Requirements to the gap MWPC
p0 fwd/bwd analysis:
e+ timing resolution is not important
because time integrated analysis is applied.
p0 left/right analysis:
e+ timing resolution is very important
because we have to measure PT precession (～200ns cycle).
• Readout: anode readout from both ends
y and z directions:
anode wire hit pattern
radial direction:
wire charge ratio.
5mm anode wire pitch corresponds to 50 ns Max. drift time.
(wire pitch is one of important parameters)
Readout methods for active polarimeter
• We need time and charge information from each wire
• Multi-hit TDC and ADC are necessary because of 10m sec gate
→ QT-converter with pipeline TDC
prop. to Q
multi-hit TDC
Leading and trading edge
should be read.
Analog sum of 12 gaps →Data size was reduced to 1/12
In case of 5mm pitch, total number of channel is 2400.
Tracking in gap MWPC
 m tracking
m trajectory is measured from wires which coincide with trigger
timing.
Drift time analysis is feasible.
 e+ tracking
e+ energy and direction should be obtained in order to increase
the experimental sensitivity (FOM)
 m stopping position
m stopping position is determined from m and e+ tracks as their
intersection point.
Simple analysis using MC simulation data
m+ stopping plate was determined
by m+ cell and e+ cell.
Identification probability is
> 98%.
Blue: m+ cell
Red: e+ cell
Preliminary results of e+ angular resolution
• Angular resolution for e+ track
m+ stopping position:
no ambiguity
e+ track:
obtained by MWPC information.
sr=0cm
sr=1cm
sr=0.5 cm
e+ angular dist.
(true-mea.) (deg)
s=5 degree was obtained.
Future plan (design of the polarimeter)
• Drift time in muon cell. Drift chamber analysis for muon track.
• Multi-cell hit by e+ are analyzed. The e+ track can be determined
more precisely.
• Realistic position resolution in radial direction.
• Test bench test using cosmic ray?