Is Isospin Conversation Required In The Standard Model?

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Discussion Overview

The discussion centers on the concept of isospin in the context of the Standard Model (SM) and its potential violations as observed in recent experimental results from BESIII. Participants explore whether the observed isospin violation in J/Psi meson decays is consistent with the Standard Model or indicative of beyond the Standard Model (BSM) physics. The scope includes theoretical implications, experimental findings, and the nature of isospin as a symmetry.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Experimental/applied

Main Points Raised

  • One participant notes that a new BESIII result indicates isospin violation in J/Psi meson decays but questions the theoretical context provided in the associated paper regarding Standard Model expectations for isospin conservation or violation.
  • Another participant states that isospin is not an exact symmetry in the Standard Model, citing the decay of phi(1020) to omega + pi0 as an example of isospin violation.
  • A participant expresses uncertainty about whether the isospin violation is attributable to Standard Model or BSM physics.
  • One participant discusses the role of chirality in relation to isospin, suggesting that isospin is not conserved in the presence of a nonzero Higgs field.
  • A later reply clarifies that the discussion of chirality pertains to weak isospin specifically, distinguishing it from the broader concept of isospin.

Areas of Agreement / Disagreement

Participants express differing views on whether the observed isospin violation aligns with Standard Model predictions or suggests new physics. There is no consensus on the implications of the findings or the definitions of isospin versus weak isospin.

Contextual Notes

Some participants highlight the lack of clarity in the theoretical background provided in the experimental papers, which may affect the interpretation of isospin violation. The discussion also reflects varying definitions and understandings of isospin and weak isospin among participants.

ohwilleke
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A new experimental result from BESIII finds that there is isospin violation in the decays of J/Psi mesons in a path involving scalar mesons (with a narrow width in tension with world averages) and notes that a previous experiment found isospin violation in another decay chain.

http://arxiv.org/abs/1505.06283

The paper's introduction, however, does little to present this finding in theoretical context. In particular, it doesn't explain the Standard Model expectation regarding isospin conservation or violation. I would think that isospin violation is permitted in the Standard Model, but only through flavor changing W boson interactions and only comparatively slowly at some small cross-section of the decay, and the paper is not at all clear regarding whether these kinds of W boson interactions are inferred.

Can anyone shed light on whether the isospin violation observed at BESIII in this paper is BSM or SM physics?

(Edited to add that the title should have said "Conservation" and not "Conversation". I'm quite certain that the Standard Model does not forbid discussions of isospin due to some grand cosmic conspiracy.)

Partially answering my own question, a previous BESIII paper on another isospin violating decay has a better theoretical background section: http://arxiv.org/abs/1502.02641
 
Last edited:
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Isospin is not an exact symmetry in the SM. For example, the phi(1020) decays to omega + pi0 a tiny fraction of the time.

Why is this in BTSM?
 
I wasn't sure if it was SM or BSM, and so asked.
 
ohwilleke said:
Can anyone shed light on whether the isospin violation observed at BESIII in this paper is BSM or SM physics?

IIUC left- and right-chirality leptons and quarks have different isospins, but they switch from left to right and back by interacting with nonzero ambient Higgs field. Thus, isospin is not a conserved charge in any vacuum with nonzero Higgs field.
 
Nikkom, that's not isospin. That's weak isospin.
 

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