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Pair-Symmetric Background Analysis

Pair-Symmetric Background Analysis. Luwani Z. Ndukum Mississippi State University. Hall C Users’ Group Meeting, Jefferson Lab, January, 2010. Motivation. World data and SANE kinematics. Recover data at low x. SANE. Outline. Introduction Effects of Background on DIS Asymmetry

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Pair-Symmetric Background Analysis

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  1. Pair-Symmetric Background Analysis Luwani Z. Ndukum Mississippi State University Hall C Users’ Group Meeting, Jefferson Lab, January, 2010

  2. Motivation • World data and SANE kinematics • Recover data at low x SANE

  3. Outline • Introduction • Effects of Background on DIS Asymmetry • Asymmetry Analysis • Pair Systematic Errors • Trajectory of an electron-positron pair in SANE • Summary

  4. Introduction • Background mostly e+ e- pair • Contamination in cerenkov • Bethe-Heitler (bremsstrahlung) • π0 decay: π0 → γ e+e- (1.2%) π0 → γγ (99%) • Correction will contribute to SSF studies

  5. Effect of Background on DIS Asymmetry • BETA is charge insensitive • The measured electron asymmetry must be corrected for the background counts and asymmetry • Need to estimate both background rate and asymmetry

  6. Asymmetry Analysis • The measured electron asymmetry • where • = measured asymmetry • = Physics asymmetry, • = Background asymmetry • = measured counts, • = fraction of background

  7. Pair Systematic Error • If we assume , but has an uncertainty given by with = e+/e- ratio • Systematic error is given by • Systematic uncertainty • > 20% for E' < 1.1 GeV • Data from table of Vipuli D., SANE report 4/21/05

  8. Pair Systematic Error • Hall C analysis from Jason Seely • Clear theta dependence • Contamination is small at large angles From: VipuliDharmawardane SANE report 4/21/05

  9. Trajectory of an e+e- pair for SANE Example: (each particle) • Pair starting direction: 40° (along BETA's axis) • Vertical deflection = 11.93° (translates to 71cm in BigCal) • 700 MeV/c corresponds to x=0.2 for DIS electrons Top side

  10. Summary • Background for SANE is mostly e+e- pairs • Clear theta dependence • Small contamination at large angles • Large magnifies error • Need to estimate both the background rate and the asymmetry • Systematic uncertainty >20% for E' < 1.1 GeV

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