1. Compton Data Analysis Jing Feng China Atomic Institute Liping Gan
University of North Carolina Wilmington

2. Contents Physics Motivation Status of the Compton Analysis Summary
Compton Events Selection
Empty target study
Efficiency of Cuts
HYCAL Response Function
Summary

3. Compton Scattering Control of systematic errors for o production
 + e-   + e-
Control of systematic errors for o production
What we measure:
Incident energy E
Scattered  energy and position
Recoil e- energy and position
Timing (Tagger-HYCAL)
For double-arm Compton runs:
PS magnet off
Lower beam intensity
The rest was same as o production runs
Data taken once per week

4. Forward Compton Cross Section

5. Compton Events Selection
Geometrical cuts:
Crystal part of HYCAL with 4 central rows excluded

6. Conservation of Energy
Kinematical Constraints
Timing cuts
Conservation of Energy
ΔE≤5σ
Δt≤(3 = 5.5 ns)
ttag-tHYCAL (ns)
Conservation of momentum Px
Co-planarity
Δφ≤22o

7. Extraction of Compton Events
Reconstructed z distance (cm)

8. X-y distribution on HYCAL(cm)
Empty target study
All Compton cuts applied but 4 central rows included
Reconstructed z (cm)
X-y distribution on HYCAL(cm)
All Compton cuts applied and 4 central rows excluded
Reconstructed z (cm)
Reconstructed Δφ

9. Efficiency of Cuts Timing cut Δφ cut Slope=-0.03% per σ

10. Efficiency of Cuts
Momentum Px cut
Slope=-0.2% per σ

11. Efficiency of Elasticity Cuts
Extracted cross sections with different ΔE cuts
Slope=1% per σ

12. HYCAL Response Function

13. Compton Cluster Energy Spectrum

14. Reconstructed Response function for Compton two-cluster Energy Sum

15. Elasticity Cuts Study via Response Function
Slope=0.1% per σ

16. Summary
A new generation Primakoff experiment has been developed to measure the lifetime of the o with high precision (~1.5%).
A state-of-the-art experimental setup, including a high precision electromagnetic calorimeter (HYCAL) and a new pair spectrometer, has been developed, constructed and commissioned.
The experiment was carried out in Fall A rich and high quality data set was collected on two targets, 12C and 208Pb.
Current data analysis demonstrates that the systematic errors can be controlled by the Compton process. We are in the process of finalizing the result on the Compton cross sections.
Long-term stability of the experiment, as measured by the Compton process, is
better than 2%.
Understanding of the systematic errors is at a level where we expect to extract o cross section with high precision.
This project is supported by the US NSF MRI grant (PHY )

17. Empty Target runs and e+e- Simulation
GEANT simulation for e+e- pairs
produced before Permanent Magnet.
Empty target run

18. Background Subtraction