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

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

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

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

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

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

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

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

Reconstructed z distance (cm) empty target subtraction

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

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

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?

HYCAL Response Function Etag-Ecluster

Compton Cluster Energy Spectrum

Reconstructed Response function for Compton two-cluster Energy Sum

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.

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

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.