International Space Agencies – Missions and Discoveries

Electron’s Electric Dipole Moment (EDM)


From UPSC perspective, the following things are important :

Prelims level: Electric Dipole Moment (EDM)

Mains level: Read the attached story


Central Idea

  • Researchers from the University of Colorado conducted an experiment to study the electric dipole moment (EDM) of an electron.
  • This EDM measurement could help solve the mystery of why there is more matter than antimatter in the Universe, which goes against the predictions of the Standard Model of particle physics.

Understanding Electron’s EDM

  • Electric Dipole Moment (EDM): The EDM of an electron is a measure of how its positive and negative electrical charges are distributed. Imagine it like a bar magnet: it shows how asymmetric the charge distribution is within the electron, as if the negative charge (electron) is not perfectly centered with respect to the positive charge (proton) within the particle.
  • Elementary Particles: Electrons are the smallest, fundamental building blocks of matter. Their EDM is an important concept in particle physics because it helps scientists study violations of certain fundamental symmetries, such as time-reversal symmetry and charge-parity symmetry.

Matter-Antimatter Asymmetry Problem

  • Matter and Antimatter: Matter and antimatter are particles with opposite charges but similar properties. According to the Standard Model, equal amounts of matter and antimatter should have been created during the Big Bang, but this is not what we observe in the Universe.
  • Annihilation: When matter and antimatter come into contact, they annihilate each other, releasing energy. This raises the question of why there is still matter around us, as both should have completely annihilated each other after the Big Bang.

Measuring the EDM:

  • EDM Measurement: By measuring the EDM of an electron, scientists can determine if the electron’s charge is perfectly centered or slightly off to one side, indicating a separation of charge.
  • Time Symmetry Violation (TSV): If an electron’s EDM is non-zero, it suggests a violation of time symmetry, meaning the behavior of particles is different when time is reversed. This violation could be a clue to explaining the matter-antimatter asymmetry.

Thesis to this dichotomy: Sakharov’s Conditions

These are three conditions proposed by physicist Andrei Sakharov to explain why there is more matter than antimatter in the Universe:

  1. Baryon Number Violation: Some processes violate the conservation of baryon number, leading to the creation of more matter than antimatter. Baryons are particles like protons and neutrons.
  2. C-Symmetry and CP-Symmetry Violation: Certain processes treat matter and antimatter differently due to violations of charge conjugation (C-symmetry) and combined charge conjugation with parity (CP-symmetry).
  3. Out-of-Equilibrium Processes: Certain processes happen out of thermal equilibrium, preventing the complete annihilation of particles and resulting in an excess of matter.

Experiment carried out

  • Complex Experimental Setup: The researchers used advanced techniques involving magnetic fields, lasers, microwaves, and radiofrequency fields to control and measure the EDM of electrons confined inside molecular ions.
  • EDM Bound: The experiment set a limit on the electron’s EDM, indicating that it is about 2.4 times higher than previously measured and roughly 1 billion times larger than predicted by the Standard Model.

Implications and Future Prospects

  • Searching for New Physics: The measurement of the electron’s EDM opens up the possibility of discovering new physics beyond the Standard Model.
  • Role in Explaining Asymmetry: The knowledge gained from EDM measurements could guide future high-energy particle colliders to produce particles that violate time symmetry, helping us understand why there is more matter than antimatter in the early Universe.

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