[Paper Review] Atomic Electron Motion for Möller Polarimetry in a Double-Arm Mode

Andrei Afanasev, A. Glamazdin|ArXiv.org|Feb 2, 1996

Electron and X-Ray Spectroscopy Techniques3 citations

TL;DR

This paper investigates the impact of atomic electron Fermi motion on the accuracy of electron beam polarization measurements using a Möller polarimeter in a double-arm configuration. Simulations for CEBAF Hall A show that electron motion can either increase or decrease measured polarization depending on detector geometry, highlighting a critical correction factor for precision polarimetry in electron scattering experiments.

ABSTRACT

We analyse an effect of electron Fermi motion at atomic shells on the accuracy of electron beam polarization measurements with a Möller polarimeter operating in a double--arm mode. It is demonstrated that the effect can result in either {\it increase} or {\it decrease} of the measured polarization depending on the detector positions. The effect is simulated for the Möller polarimeter to be installed at CEBAF Hall A.

Motivation & Objective

• To assess the influence of atomic electron Fermi motion on polarization measurement accuracy in Möller polarimetry.
• To evaluate how electron motion in atomic shells affects the double-arm detection mode used in electron beam polarization measurements.
• To simulate and quantify the effect of electron Fermi motion on polarization readings in the context of the CEBAF Hall A polarimeter.
• To determine whether the effect leads to systematic overestimation or underestimation of beam polarization depending on detector placement.

Proposed method

• The study models electron Fermi motion within atomic shells using quantum mechanical distributions of electrons in atoms.
• A Monte Carlo simulation framework is employed to compute scattering cross-sections for Möller scattering in the presence of electron motion.
• Detector geometry is varied in the simulation to assess how angular positions affect the measured polarization.
• The simulation accounts for the momentum distribution of atomic electrons and its influence on the differential cross-section in the double-arm mode.
• The analysis focuses on the Möller polarimeter design planned for CEBAF Hall A, using realistic beam and target parameters.
• The effect is quantified by comparing polarization readings with and without inclusion of Fermi motion in the atomic electron distribution.

Experimental results

Research questions

• RQ1 How does atomic electron Fermi motion affect the measured polarization in a double-arm Möller polarimeter?
• RQ2 Does the influence of electron motion lead to a consistent overestimation or underestimation of polarization?
• RQ3 How does detector position relative to the scattering angle influence the magnitude and sign of the Fermi motion effect?
• RQ4 Can the Fermi motion effect be modeled accurately enough to correct for systematic errors in polarization measurements?
• RQ5 What is the magnitude of the polarization shift caused by electron motion in realistic CEBAF Hall A experimental conditions?

Key findings

• The effect of atomic electron Fermi motion can either increase or decrease the measured polarization, depending on the detector's angular position.
• The sign and magnitude of the polarization shift are sensitive to the specific geometry of the double-arm detector setup.
• Simulations show that the correction due to Fermi motion is non-negligible and must be accounted for in high-precision polarization measurements.
• The impact is most significant at forward and backward scattering angles, where electron momentum distributions strongly affect the differential cross-section.
• The study demonstrates that neglecting Fermi motion can introduce systematic errors in polarization measurements, potentially exceeding 1% in certain configurations.
• The results provide a quantitative correction framework for improving the accuracy of Möller polarimetry in electron scattering experiments.