1. Compton Data Analysis Liping Gan University of North Carolina Wilmington

2. 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

3. Forward Compton Cross Section  Different results are within 5% agreement  Current acceptance based on K-N cross section only

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

5. Conservation of Energy Co-planarity Kinematical Constraints Timing cuts Δt≤(3  = 5.5 ns) t tag - t HYCAL ( ns) ΔE≤5σ Δφ≤22 o Conservation of momentum P x

6. Extraction of Compton Events Reconstructed z distance (cm) without empty target subtraction

7. Empty target study All Compton cuts applied but 4 central rows included All Compton cuts applied and 4 central rows excluded Reconstructed z (cm) Reconstructed Δ φ X-y distribution on HYCAL(cm) Etag-Erec

8. Efficiency of Cuts Timing cut Δφ cut Slope=0.2% per σ Slope=-0.03% per σ

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

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

11. HYCAL Response Function E tag -E cluster

12. Compton Cluster Energy Spectrum

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

14. 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.

15. Main tasks in experimental part Understand the sensitivity of the elasticity cut.Understand the sensitivity of the elasticity cut. – Hard double Compton effect? – Scattering electron radiative tail? Contribution from hard double Compton processContribution from hard double Compton process Acceptance study including:Acceptance study including: – corrections to Compton differential cross section – multiple scattering of electron in the target – scattering photon absorption in the target – beam stability

16. Corrections to integrated forward (0.325 o <θ<3.60 o ) cross sections Slope is about 1% per σ !

17. Where we are in theory calculation? Calculate soft-virtual cross section and hard double Compton cross section separately:Calculate soft-virtual cross section and hard double Compton cross section separately: – Calculate hard double Compton cross section by Monte Carlo in order to implement all Compton cuts. (Program is ready) – Calculate cross section contributed from single Compton,Virtual Compton, and soft double Compton. (Result will be available in two weeks)

18. Summary  Monte Carlo Program including radiative corrections and double Compton effect is developed and ready to use.  Two graduate students from China will join us shortly.  We expect to have some solid results by middle of March