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PEPPo Collaboration Meeting

Status and Performances of the E166 Modified Calorimeter. Maud Baylac ǂ , Germain Bosson ǂ , Jonathan Dumas ǂ* , Marc Marton ǂ , Jean-François Muraz ǂ , Jean-Sébastien Réal ǂ , Eric Voutier ǂ. ǂ Laboratoire de Physique Subatomique et de Cosmologie Grenoble, France

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PEPPo Collaboration Meeting

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  1. Status and Performances of the E166 Modified Calorimeter Maud Baylacǂ, Germain Bossonǂ, Jonathan Dumasǂ*, Marc Martonǂ, Jean-François Murazǂ, Jean-Sébastien Réalǂ, Eric Voutierǂ ǂ Laboratoire de Physique Subatomique et de Cosmologie Grenoble, France * Thomas Jefferson National Accelerator Facility Newport-News, Virginia, USA • E166 configuration • PEPPo configuration • PMT read-out • Calorimeter operation • Workplan PEPPo Collaboration Meeting November 8-9, 2010, Newport News

  2. E166 Configuration Eric Voutier Principle of Operation G. Alexander et al, PRL 100 (2008) 210801 G. Alexander et al,NIM A 610 (2009) 451 • The E166 experiment operated with high incident particle flux, integrating the energy deposited in the crystal per beam pulse and per target polarization orientation. • The signal read-out was realized with BaBar inspired electronics, relying on Hamamatsu S2744-08 photodiodes, a set of amplifiers, and ADCs. Small experimental asymmetries and large polarization transfer from circularly polarized photons to longitudinally polarized positrons have been reported. Experimental proof of the undulator based polarized positron source for ILC. 2/14 Newport News, November 8-9, 2010

  3. E166 Configuration Eric Voutier K. Laihem, PhD Thesis, Humboldt Universität zu Berlin (2008) 2.8 MeV Cosmics • The high energy response of the crystals is quite good and well understood. • Electronics noise is a matter of concern for small energy deposit. • Energy resolution at small energy deposit does not look impressive. 3/14 Newport News, November 8-9, 2010

  4. PEPPo Configuration Eric Voutier Principle of Operation • PEPPo will investigate the longitudinal polarization transfert from polarized electrons to polarized positrons. • Experimental asymmetry will be measured with respect to the electron beam helicity for a given target polarization orientation. • We aim at three different analysis schemes of the experimental signal: integrated (similar to E166), semi-integrated (energy distributed asymmetry and built-in pulse shape analysis), and event-by-event (energy distributed asymmetry and off-line pulse shape analysis). The PMT read-out is expected to improve the signal-to-noise ratio and the resolution at small photon energies. 4/14 Newport News, November 8-9, 2010

  5. PMT Read-Out Eric Voutier Top cosmic trigger VME DAQ Wiener VME VM-USB controler CAEN ADC V792 NC CAEN TDC V 775 AC CAEN DFC Calorimeter box 5/14 Newport News, November 8-9, 2010

  6. PMT Read-Out Eric Voutier PMT Base Typical PMT cosmic signal at 1000 V high voltage with a standard Hamamatsu base. • Expected high particle flux and large operational high voltage reduce the PMT life-time. Custom PMT bases are designed for PMT gain reduction and output signal amplification. 6/14 Newport News, November 8-9, 2010

  7. PMT Read-Out Eric Voutier Cosmic Test Top trigger • The trigger scintillator strips overlap longitudinally the CsI crystal and define a transverselocation close to the PMT side. • HV = 1200 V Dt = 2.5 µs • After 4 data taking days… Crystal Bottom trigger 16 db 16 db 16 db About 50 MeV energy deposit for perpendicular minimum ionizing particles. 7/14 Newport News, November 8-9, 2010

  8. PMT Read-Out Eric Voutier Signal Characterization HV = 1400 V Dt = 2.0 µs Th. = 15 mV 22Na ( 0.511 MeV, 1.275 MeV) 22Na source Crystal box 1.275 MeV • The test is performed with the same light collection surface as E166 configuration. 8/14 Newport News, November 8-9, 2010

  9. PMT Read-Out Eric Voutier • The effective efficient duration of the signal is about 2 µs. 9/14 Newport News, November 8-9, 2010

  10. PMT Read-Out Eric Voutier Optical fiber for LED monitoring of the experimental chain • Improved light collection surface together with a direct coupling of the PMT to the crystal using an optical gel. 20 x 20 → 54 x 54 (surface factor = 7.3) 10/14 Newport News, November 8-9, 2010

  11. PMT Read-Out Eric Voutier HV = 1300 V Dt = 2.0 µs Th. = 7 mV Pedestal 1.275 MeV 0.511 MeV 0.511 MeV 1.275 MeV 22Na (2 mn DataK) Background (860 mn DataK) • The improvement of the surface collection and PMT-crystal optical coupling leads to a 100 V gain on the operational high voltage. • Unexpected behaviours appear… DAQ issues… On-going investigations… 11/14 Newport News, November 8-9, 2010

  12. Calorimeter Operation Eric Voutier Compton Transmission Polarimetry • Polarized e± convert into circularly polarized photons into a tungsten target. • The photon polarization is analyzed via Compton scattering off a magnetized iron target. T = 7.5 MeV P = 85% tw = 1 mm I = 1 pA Dt = 100 s • The analyzing power Ae is obtained from electron beam calibration data and simulations. • High DAQ rates capabilities will be obtained with the flash ADC FADC 250 developped at JLab. DPe = ±0.03 12/14 Newport News, November 8-9, 2010

  13. Calorimeter Operation Eric Voutier Experimental Issues IM Integrated Method SIM Semi Integrated Method EVEM Event-by-Event Method • ADC samples for a fixed time window (2-3µs) are tagged by helicity state. • Each ADC sample per crystal, helicity state, and event is registered (9 x 750 values). • The DAQ trigger should be external (positron counter ?). • Sizeable asymetries are expected. • Threshold, pile-up, and dead-time issues. • No helicity correlated background concerns. • ADC samples are summed over the time duration of the helicity gate. • The total energy deposited in a crystal per helicity state is registered (2 x 9 values). • The DAQ trigger is the helicity gate. • Small asymmetries are expected. • No threshold, pile-up or dead-time concerns. • Potential helicity correlated background issues. • ADC samples per event are summed for a fixed time window and tagged by helicity state. • The energy deposit per crystal, helicity state, and event is registered (2 x 9 x nb of energy bins values). • The DAQ trigger should be external (positron counter ?). • Sizeable asymmetries are expected. • Threshold or pile-up issues but no dead-time concerns. • No helicity correlated background concerns. 13/14 Newport News, November 8-9, 2010

  14. Workplan Eric Voutier Technical Issues • Calorimeter Construction • Operation of the local electronics and DAQ system • Development of an improved cosmic trigger (scintillator hodoscope, lead absorber for MIPs selection… ); possible use at JLab ? • - Selection of the wrapping material (tyvek, aluminized mylar, millipore…) • Quality tests of the crystals (signal-to-noise ratio, resolution…) • Test of the LED monitoring system • Test of the modified calorimeter before shipment to JLab (mechanics, PMT bases…) • Calorimeter Operation • Operation of the calorimeter with the FADC 250 • Development of solutions and practices for each experimental issues • Exhaustive simulations (analyzing power, transverse polarization effects, misalignement effects, positron distribution sensitivity… ) • … 14/14 Newport News, November 8-9, 2010

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