Active polarimeter simulation

Suguru ShimizuOsaka University

Sep. 1, 2007JPARC TREK Collaboration meeting at Saskatchewan

Assembly of Active polarimeter Identification of muon stopping point/ decay vertex Measurement of positron energy Ee+ and angle e+ Large positron acceptance of nearly 4 Higher sensitivity Lower BG in positron spectra

Parallel plate stopper withGap MWPC Number of plates 31 Plate material Al, Mg or alloy Plate thickness ~ 2 mm Plate gap ~ 8 mm Ave. density 0.24 Al

stop efficiency ~ 85%

Small systematics for L/R positron Fit for 0 fwd/bwd measurement

Plates are ground　 potential

Muon stopping distribution in the stopper

t/d = const.

d=2 mm

d=8 mm d (mm)

d = 8 mm

t=2 mm

t = 0. 5 mm

(g/cm3)

= 0.2Al

= 0.54 g/cm3

stop > 85% for t = 2 mm d =8 mm

Stopping prob. is determined by effective density.

Readout assembly for gap MWPC• Requirements to the gap MWPC

0 fwd/bwd analysis: e+ timing resolution is not important because time integrated analysis is applied. 0 left/right analysis:e+ timing resolution is very important because we have to measure PT precession ( ～ 200ns cycle).

• Readout: anode readout from both endsy and z directions: anode wire hit patternradial 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 10 sec gate

→ QT-converter with pipeline TDC

Analog sum of 12 gaps →Data size was reduced to 1/12In case of 5mm pitch, total number of channel is 2400.

prop. to Q multi-hit TDC Leading and trading edge should be read.

Tracking in gap MWPC tracking

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)

stopping position stopping position is determined from and e+ tracks as their intersection point.

Simple analysis using MC simulation data

Identification probability is > 98%.

Blue: + cellRed: e+ cell

+ stopping plate was determined by + cell and e+ cell.

Preliminary results of e+ angular resolution• Angular resolution for e+ track

+ stopping position: no ambiguitye+ track: obtained by MWPC information.

r=0cm

r=1cm

r=0.5 cm

e+ angular dist. (true-mea.) (deg)

=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?