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Active polarimeter simulation

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 E e + and angle q e +

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Active polarimeter simulation

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

  2. 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 • 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 rAl m+ stop efficiency ~ 85% • Small systematics for L/R positron • Fit for p0fwd/bwd measurement Plates are groundpotential

  3. Muon stopping distribution in the stopper r= 0.2rAl = 0.54 g/cm3 estop > 85% for t = 2 mm d =8 mm t/d = const. d=2 mm d=8 mm d (mm) d = 8 mm t=2 mm t = 0. 5 mm r (g/cm3) Stopping prob. is determined by effective density.

  4. 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)

  5. 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 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 • m trackingm 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 positionm stopping position is determined from m and e+ tracks as their intersection point.

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

  8. Preliminary results of e+ angular resolution • Angular resolution for e+ trackm+ stopping position: no ambiguitye+ track: obtained by MWPC information. sr=0cm sr=0.5 cm e+ angular dist. (true-mea.) (deg) sr=1cm s=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?

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