1. 1 First Results of the SLD Cerenkov Polarimeter at the DESY test beam Oleg Eyser Daniela K äfer, Christian Helebrant, Jenny List, Ulrich Velte*

2. 2 A Cerenkov detector Cerenkov drift section Transmission line R1398 PMTs 9 channels 234567891 channel assignment

3. 3 DESY II Test Beam

4. 4 Test Beam Area 21 movable tableelectrons+trigger HV & DAQ detector

5. 5 Setup Trigger HV DiscriminatorGateADC delay PC Control RoomTable Remote 3 GeV electrons z x y November 2007: old PMTs 2 weeks with setup and first tests Channels 1 & 2 bad Channel 3 dead December 2007: some channels with SiPMs and multi-anode PMTs Four days before holidays Two dead channels (4 & 6) C 4 F 10 20 mbar overpressure

6. 6 Data Acquisition typically 200,000 to 1,000,000 events pure Poisson distribution Fit: Poisson  Gauss  Photo electrons  Effective gain  Pedestal channel 5 charge

7. 7 Voltage Scan 1700 V 1750 V 1800 V 1850 V charge Gain varies by a factor of two between channels (compare errors) Working point at 1850 V

8. 8 Cross Talk charge ch.4 ch.5 ch.6 signal shape in channel 5 (from table scan) noise region

9. 9 Table Scan channel 5 channel 4 channel 6 channel 7 Detector position (mm) Channel width 10 mm Fold with beam spread and Trigger:

10. 10 Compare Simulation 3 GeV electrons, σ x = 5 mm C 4 F 10 refraction index n ≈ 1.0014 Detector box walls 5 mm Channel walls 500 μm Reflectivity 92% 20 cm Cerenkov drift section 30-40 photons (200-650 nm) Quantum efficiency ( =20%)

11. 11 Pre-Radiator charge D-box only 3 mm tungsten 6 mm tungsten X 0 = 0.35 cm Meant to increase: electrons  photons  signal Dilutes the spectra instead scatt. angles above 4 o cross two tubes Thin tungsten bars in front of the detector

12. 12 Rotated Detector Transmission line 40-80 cm Increased photon yield (factor 2 – 4) channel 5 Additional gain due to reflection z x

13. 13 ILC Polarimeter: a quick draft Uses electron spectra from fast simulation Can then use ADC spectra to develop analysis technique z x x y z C4F10 in the vacuum chamber

14. 14 Summary Two Test Beam Periods –with old and new photo detectors –Detector layout is well understood –New data needs to be analyzed New Layout can be simulated –Compton spectra from fast simulation (include polarization) –Plan test beam with comparable electron intensity (10 3 ) –Tube design Polarization Measurement –Analyzing power extraction from electron spectra / asymmetry –Wall effects, bunch intensity, laser-electron alignment