Electron mass without B-field: best precision?

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SUMMARY

The discussion focuses on determining the electron charge-to-mass ratio (e/m_e) without using magnetic fields, contrasting with the highly precise Penning-trap cyclotron frequency measurements that rely on strong magnetic fields. Alternative methods such as LINAC kinematics and Duane-Hunt bremsstrahlung currently achieve only 2–10% precision, which is significantly less accurate. A promising approach involves combining direct charge measurements, like the Millikan oil drop experiment, with hydrogen spectroscopy dominated by electric fields to independently determine e/m_e without magnetic fields. This combined method offers a potential pathway to improve precision outside of magnetic field-based techniques.

PREREQUISITES

  • Penning-trap cyclotron frequency measurement techniques
  • LINAC (Linear Accelerator) kinematics and operation principles
  • Duane-Hunt bremsstrahlung radiation theory
  • Millikan oil drop experiment and hydrogen atomic spectroscopy

NEXT STEPS

  • Investigate precision limits of combining Millikan charge measurements with hydrogen spectroscopy
  • Review recent experimental data on LINAC-based e/m_e determinations
  • Analyze improvements in Duane-Hunt bremsstrahlung measurement techniques
  • Explore theoretical models for electric-field-dominated spectroscopy for fundamental constant extraction

USEFUL FOR

Physicists specializing in fundamental constant measurements, experimental atomic physicists, researchers developing non-magnetic precision measurement techniques, and accelerator physicists interested in alternative methods for determining electron charge-to-mass ratio.

Roberto Pavani
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TL;DR
What is the most precise determination of the electron mass (or ##e/m_e##) that does not rely on a magnetic field?
The CODATA value of ##e/m_e## comes from Penning-trap cyclotron frequency measurements (strong ##B## field). Are there any competitive determinations of the same ratio ##e/m_e## using purely electric methods (no ##B##)? For instance from LINAC kinematics or Duane-Hunt bremsstrahlung? The papers I found have precisions of only 2–10%. Is there anything better?
 
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Linacs need to know that ratio to work, but they might not measure and publish that ratio as we already have way more precise measurements elsewhere.

In principle you can combine a direct charge measurement (-> Millikan) with spectroscopy of hydrogen (dominated by electric fields) to find the ratio.
 
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Thank you mfb. The idea of combining a direct charge measurement with hydrogen spectroscopy is a useful pointer. I'll look into what precision that route can achieve independently of ##B##-field methods.
 

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