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  + e-   + e-
Control of systematic errors for o production
Precision Measurement of Compton Cross section at a few GeV region for the first time

4. Forward Compton Cross Section
Different results are within 5% agreement
Some patterns of tagger T count dependence
Current acceptance based on K-N cross section only

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) without empty target subtraction

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)
Etag-Erec
All Compton cuts applied and 4 central rows excluded
Reconstructed z (cm)
Reconstructed Δφ

9. Reconstructed z distance (cm) empty target subtraction

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

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

12. Efficiency of Elasticity Cuts
Extracted cross sections with different ΔE cuts
Slope is ~1% per σ
What is the cause of strong sensitivity of elasticity cut?

13. HYCAL Response Function
Etag-Ecluster

14. Compton Cluster Energy Spectrum

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

16. Elasticity Cuts Study via Response Function
Slope=0.1% per σ
The strong sensitivity of elasticity cut for Compton events selection (~1% per σ) can not be explained by HYCAL response function.

17. What to do next? Understand the sensitivity of the elasticity cut.
Acceptance study including: (1) corrections to Compton differential cross section (2) multiple scattering of electron in the target (3) scattering photon absorption in the target (4) beam stability
Background study
Long term stability
Differential cross section

18. Summary
Compton cross section is currently ~3-5%
There are still work need be done to reduce systematic errors in order to provide a reliable tool to calibrate over all systematic error for o analysis.