Understanding the puzzle of angular momentum conservation in beta decay and related processes
- URL: http://arxiv.org/abs/2405.15011v2
- Date: Wed, 4 Sep 2024 15:26:08 GMT
- Title: Understanding the puzzle of angular momentum conservation in beta decay and related processes
- Authors: Gordon Baym, Jen-Chieh Peng, C. J. Pethick,
- Abstract summary: We ask the question of how angular momentum is conserved in electroweak interaction processes.
We consider inverse beta decay in which an electron is emitted following the capture of a neutrino on a nucleus.
While both the incident neutrino and final electron spins are antiparallel to their momenta, the final spin is in a different direction than that of the neutrino.
We generalize the discussion to massive neutrinos and electrons, and examine nuclear beta decay and electron-positron annihilation processes through the same lens.
- Score: 0.0
- License: http://creativecommons.org/licenses/by/4.0/
- Abstract: We ask the question of how angular momentum is conserved in electroweak interaction processes. To introduce the problem with a minimum of mathematics, we first raise the same issue in elastic scattering of a circularly polarized photon by an atom, where the scattered photon has a different spin direction than the original photon, and note its presence in scattering of a fully relativistic spin-1/2 particle by a central potential. We then consider inverse beta decay in which an electron is emitted following the capture of a neutrino on a nucleus. While both the incident neutrino and final electron spins are antiparallel to their momenta, the final spin is in a different direction than that of the neutrino -- an apparent change of angular momentum. However, prior to measurement of the final particle, in all these cases angular momentum is indeed conserved, 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 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.
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