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THE NEW FOCAL PLANE POLARIMETER
IN HALL C HALL C USERS MEETING, January 18, 2008 Mehdi MEZIANE, the College of William and Mary
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OUTLINE INTRODUCTION ROSENBLUTH SEPARATION
POLARIZATION TRANSFER METHOD HMS TRIGGER FOCAL PLANE POLARIMETER (FPP) FPP DRIFT MAPS FPP EFFICIENCY CONCLUSION
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Two methods to obtain the form factors of the proton:
INTRODUCTION Two methods to obtain the form factors of the proton: Rosenbluth separation of cross section data which gives and Measurement of the ratios using the recoil polarization technique The results of these two techniques are incompatible above a of
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ROTHENBLUTH / TRANSFERT
POLARIZATION DATA Recoil polarization and Rosenbluth ratios are clearly different. Difference increase systematically with Q2.
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ROSENBLUTH SEPARATION
Cross section: with Jlab experiment : I.A. Quattan et al., Phys. Rev. 94, (2005).
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POLARIZATION TRANSFER METHOD
The transferred polarization is: with Independent of : the analysing power the beam polarization
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ASYMMETRIES Measure asymmetry distribution after rescattering in the analyser For 2 helicities of beam (±1) with polarization Pe , relative asymmetry in the polarimeter is: With and the physical polarizations at the FPP , the analysing power , the azymuthal scattering anlge
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ASYMMETRIES The physical asymmetries are calculated from the difference distributions: φ (°) Di
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HMS TRIGGER NEW HMS trigger HMS S2 detector is physically REMOVED
Use of HMS S1 detector and a new S0 detector HMS S2 detector is physically REMOVED S0 is divided in two parts: S0X1 and S0X2 S1 S0X1 S0X2 S1&S0X1 HMS hut trigger S1&S0X2 Trigger Supervisor &
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S0 DETECTOR 4 PMTs 2 scintillators 2 wave shifters
Central trajectory Ebeam = GeV Ebeam = GeV Ebeam = GeV Upper part: S0X1 (part of inelastic) Lower part: S0X2 (elastic)
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HMS TRIGGER NEW HMS trigger HMS S2 detector is physically REMOVED
Use of HMS S1 detector and a new S0 detector HMS S2 detector is physically REMOVED S0 is divided in two parts: S0X1 and S0X2 S1 S0X1 S0X2 S1&S0X1 HMS hut trigger S1&S0X2 Trigger Supervisor &
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Focal Plane Polarimeter (FPP) in Hall C
u x v 4 Chambers with 3 planes each 12 planes of detection Active area 134*166 (cm2) 2 split CH2 analysers 145 *111* 60 (cm3) Gas mixture Argon50%/Ethane50% Operating HV 2350V (field and cathode wires)
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Focal Plane Polarimeter (FPP) in Hall C
HMS Drift Chambers: S0 and S1 CH2 analysers FPP Drift Chambers
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Focal Plane Polarimeter (FPP) in Hall C
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FPP Read Out System twisted pair ribbon cables (1 for 2 cards)
Amplifier/read out cards 1 card for 8 sense wires ECL logic signals 37 cards per chamber TOTAL of 148 cards VME based F1-TDC
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FPP Drift Maps Mapping this distribution Time/distance
Background window Mapping this distribution into a flat distance distribution Time/distance correlation Drift Time + Subtracting background
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FPP efficiency: Straight Through
At the beginning of each kinematic 1 hour of straight through data (WITHOUT analyser) are taken. The efficiency in FPP1,2 is: FPP 1, 2 refers to chamber pair A&B and C&D respectively ε = 86% for FPP1 ε = 85% for FPP2
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HMS/FPP 2D correlation cm cm Chamber A cm Chamber C cm
Predicted drift distance based on HMS and FPP wire hit information VS Calculated FPP drift distance
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FPP efficiency: N5hits / N6hits
The efficiency ε per plane is given by: > 98.6% with the ratio: (6 planes of detection) The efficiency per pair of chambers is then : ~ 92% Then the efficiency for 5 OR 6 planes hit is : > 99.7%
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FPP 6 planes efficiency evolution
1) Back to the nominal HMS threshold 6.8V 5.5V 2) HMS/FPP gas problem fixed
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FPP1,2 ASYMMETRIES, Q2 = 2.5 GeV2 Di Q2 = 2.5 GeV2 Ebeam = 3.539 GeV
Di vs φ φ (°) Q2 = 2.5 GeV2 Ebeam = GeV θe = 32.9° 24 M triggers
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GEP 2γ ERRORS
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CONCLUSION New HMS trigger with a new S0 detector
Good drift maps computation FPP Straight through efficiency of 85% 5 OR 6 plane FPP efficiency above 99.7%
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