Date
March 21 (Fri) at 14:00 - 15:30, 2025 (JST)
Speaker
  • Gordon Baym (Professor Emeritus, University of Illinois, USA)
Language
English
Host
Tetsuo Hatsuda

This is a iTHEMS-FQSP joint seminar.

We ask the question of how angular momentum is conserved in a number of related processes, from elastic scattering of a circularly polarized photon by an atom, where the scattered photon has a different spin direction than the original photon; to scattering of a fully relativistic spin-1/2 particle by a central potential; to inverse beta decay in which an electron is emitted following the capture of a neutrino on a nucleus, where the final spin is in a different direction than that of the neutrino – an apparent change of angular momentum.

The apparent non-conservation of angular momentum arises in the quantum measurement process in which the measuring apparatus does not have an initially well-defined angular momentum, but is localized in direction in the outside world. We generalize the discussion to massive neutrinos and electrons, and examine nuclear beta decay and electron-positron annihilation processes through the same lens, enabling physically transparent derivations of angular and helicity distributions in these reactions.

Reference

  1. Gordon Baym, Jen-Chieh Peng, and C. J. Pethick, Understanding the puzzle of angular momentum conservation in beta decay and related processes, doi: https://www.pnas.org/doi/abs/10.1073/pnas.2416768121

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