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 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

Forward Compton Cross Section

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)

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

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=1% per σ

HYCAL Response Function

Compton Cluster Energy Spectrum

Reconstructed Response function for Compton two-cluster Energy Sum

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

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 2004. 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-0079840)

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

Background Subtraction