Positron Asymmetry and Polarization from the E166 September 2005 run

1. DESY/Hamburg, 1-Nov-06 Positron Asymmetry and Polarizationfrom the E166 September 2005 run Gideon Alexander & Erez Reinherz-Aronis

2. Analyzing magnet (-60/+60) CsI e+ γ Spectrometer Lens Bend magnets γ detectors γ e- Undulator SLC e- e- Analyzing magnet (-60/+60) W-Target E-166 Schematic view

3. Some General Guidelines and Comments • Presently only the central CsI crystal (Crystal #5) was considered. A preliminary look into nearby crystals has been started. • We chained all the events belonging to the same energy together under the reasonable expectation that local variations will, to a large extend, average out. • We tried to avoid as much as possible arbitrary, unique cuts and procedures. • Instead, we preferred to study by how much the results depend on the a priori range of different possible procedures and cuts from which one could choose.{e.g, tried Low sensitivity (12 bit) and High sensitivity (15 bit)}. The spread of some of these results may serve later as one input to the systematic errors.

4. Selection of Runs and Events • 1st stage: • SuperRuns. • Runs with Spectrometer and Lens values • Runs were rejected when • Empty runs. • Beam off. • 15 Hz runs. • 2nd stage • Pairs of events were accepted by ‘Trigger’ word. Note: Events with ADC above 4000 were filtered out.

5. The main use of the toroid 6130 • The toroid currents was used to define the appropriate range of the data, taking ±2σ range from an overall Gaussian fit. • The analysis was then carried out with and without a toroid normalization.

6. 160 A Positron Asymmetry • Event Pair : Signal*, Background (Bg). • Gaussian Fit in general is poor so we use it only to define the sample range (σ cut, we also studied by how much the results depend on this specific choice). • For each spectrometer value we calculate L and R via the mean: *Signal = Signal over Background (Signal + Bg)

7. 306 K 278 K 602 K 265 K 242 K Events Fraction of L events surviving the cuts (low sensitivity)

8. Fraction of L events surviving the cuts (high sensitivity) 306 K 278 K 602 K 265 K 242 K Events

9. Asymmetry Error • For a Gaussian distribution:

10. Asymmetry Error • Note: Gaussian Fit in general is very poor (χ2/d.o.f. >> 1) • But one can estimate σ2 by • so that the Asymmetry error can be written as

11. Error dependence on the σ cut (spec = 160 [A])

12. Asymmetry results Gain 1, Low sensitivity (12 bit)

13. Asymmetry results Gain 1, High sensitivity (15 bit)

14. Comparison between Berlin and TA. positrons asymmetries

15. Positron Polarization Ae+ Analyzing power

16. Positron Polarization Using Ae+ from GEAT4

17. Positron Polarization Using Ae+ from GEAT4

18. Some final remarks • It is very assuring thatthe two analyses yielded essentially the same asymmetry values so that together they enhance the confidence in the undulator-based method to produce longitudinal polarized positrons. • The errors given are essentially the statistical ones and one should expect that the final errors will be dominated by the systematic ones. • It is reassuring that the positron polarization values and behavior as a function of energy corresponded to there expectations. • The electrons asymmetry seems to be significantly higher than that of the positrons. This observation demands some more study.

19. Positron Asymmetry and Polarizationfrom the E166 September 2005 run Gideon Alexander & Erez Reinherz-Aronis

20. Values for the Analyzing Power Ae+ Extracted from Table 13, E-166 Proposal, June 2003 (Averages).

21. Backup 5 Backup - Toriod cuts