1. Active polarimeter simulation Suguru Shimizu Osaka University Sep. 1, 2007 JPARC TREK Collaboration meeting at Saskatchewan

2. Assembly of Active polarimeter Identification of muon stopping point/ decay vertex Measurement of positron energy E e + and angle  e + Large positron acceptance of nearly 4  Higher sensitivity Lower BG in positron spectra Parallel plate stopper with Gap 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

3. 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/cm 3 )  = 0.2  Al = 0.54 g/cm 3  stop > 85% for t = 2 mm d =8 mm Stopping prob. is determined by effective density.

4. 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 P T 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)

5. 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 1/12 In case of 5mm pitch, total number of channel is 2400. prop. to Q multi-hit TDC Leading and trading edge should be read.

6. 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.

7. Simple analysis using MC simulation data Identification probability is > 98%. Blue:  + cell Red: e + cell  + stopping plate was determined by  + cell and e + cell.

8. Preliminary results of e + angular resolution Angular resolution for e + track  + stopping position: no ambiguity e + track: obtained by MWPC information.  r =0cm  r =1cm  r =0.5 cm e + angular dist. (true-mea.) (deg)  =5 degree was obtained.

9. 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?