Is Isospin Conversation Required In The Standard Model?

In summary, the recent experimental result from BESIII shows evidence of isospin violation in the decays of J/Psi mesons, specifically in a path involving scalar mesons with a narrow width. This finding is in tension with previous world averages and the paper's introduction lacks theoretical context regarding the Standard Model's expectation for isospin conservation or violation. However, previous BESIII research on another isospin violating decay provides a better theoretical background. Isospin is not a conserved charge in any vacuum with nonzero Higgs field, as left- and right-chirality leptons and quarks have different weak isospins that can switch by interacting with the ambient Higgs field. Therefore, it is unclear whether the
  • #1
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
 
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  • #2
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?
 
  • #3
I wasn't sure if it was SM or BSM, and so asked.
 
  • #4
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.
 
  • #5
Nikkom, that's not isospin. That's weak isospin.
 

1. What is isospin conservation in the Standard Model?

Isospin conservation is a fundamental principle in the Standard Model of particle physics, which states that the total isospin of a system must remain constant during interactions. Isospin is a quantum number that describes the intrinsic properties of subatomic particles, specifically their strong nuclear force interactions. This conservation law is essential for understanding the behavior of particles in the atomic nucleus and the formation of nuclear forces.

2. Why is isospin conservation necessary in the Standard Model?

In the Standard Model, isospin conservation is necessary because it is a fundamental symmetry that governs the behavior of particles under the strong nuclear force. It helps to explain why certain particles interact in specific ways and why certain interactions are forbidden. Without this conservation law, the Standard Model would not accurately describe the behavior of subatomic particles.

3. How does isospin conservation affect particle interactions?

Isospin conservation affects particle interactions by limiting the possible outcomes of a particle interaction. For example, in a nuclear reaction, the total isospin of the initial particles must be the same as the total isospin of the final particles. This conservation law also determines the types of particles that can be produced in particle collisions and the ways in which they can decay.

4. What evidence supports the need for isospin conservation in the Standard Model?

There is a significant amount of experimental evidence that supports the need for isospin conservation in the Standard Model. For example, the analysis of particle collisions at high-energy accelerators, such as the Large Hadron Collider, consistently confirms the conservation of isospin. Additionally, the precise predictions of the Standard Model, which include isospin conservation, have been confirmed through numerous experiments.

5. Are there any exceptions to isospin conservation in the Standard Model?

While isospin conservation is a fundamental principle in the Standard Model, there are a few exceptions to its strict application. These exceptions occur in certain rare or highly energetic interactions, where the effects of other fundamental forces, such as electromagnetism, can temporarily overcome the effects of the strong nuclear force. However, these exceptions do not invalidate the overall importance and necessity of isospin conservation in the Standard Model.

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