Baryon CP Violation Observed at CERN

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Discussion Overview

The discussion centers around the recent observation of CP violation in the decay of beauty baryons by the LHCb collaboration. Participants explore whether this observation aligns with predictions from the Standard Model (SM) and its implications for understanding matter-antimatter asymmetry in the universe. The conversation includes theoretical implications, challenges in calculations, and comparisons to previous observations in mesons.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants note that CP violation has been previously observed in mesons, making this the first observation in baryons.
  • Questions arise regarding whether this observation was predicted by the Standard Model and what constraints it may impose on SM parameters.
  • There is mention of a different mechanism detected in the paper that could explain CP violation, which is still consistent with the Cabibbo theory but has a larger amplitude.
  • Some participants express uncertainty about whether the results are considered within or outside the Standard Model, citing difficulties in calculating necessary terms due to complex chromodynamics.
  • One participant highlights that while the SM predicts CP violation in quark processes, the new results do not definitively rule out the involvement of physics beyond the SM.
  • A question is raised about the comparatively small CP violation in baryons versus mesons, suggesting a potential paradox.

Areas of Agreement / Disagreement

Participants do not reach a consensus on whether the observed CP violation is fully explained by the Standard Model or if it indicates new physics. Multiple competing views remain regarding the implications of the findings.

Contextual Notes

Participants note challenges in calculations related to chromodynamics, which may affect interpretations of the results. There are also unresolved questions about the implications for matter-antimatter asymmetry.

Who May Find This Useful

Researchers and students interested in particle physics, CP violation, and the implications for the Standard Model and beyond may find this discussion relevant.

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TL;DR
CERN announces observation of CP violation in the decay of the beauty baryon.
The LHCb collaboration has announced that they have observed CP violation in the decay of the beauty baryon. The Nature paper is here:

https://www.nature.com/articles/s41586-025-09119-3

And the arxiv preprint is here:

https://arxiv.org/pdf/2503.16954

According to the paper, CP violation has previously been observed in mesons, but this is the first observation of it in baryons.
 
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Was this a prediction of the standard model or something new? If it was already a prediction, does the measurement put new constraints on any of the standard model parameters?
 
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Dale said:
Was this a prediction of the standard model or something new? If it was already a prediction, does the measurement put new constraints on any of the standard model parameters?
According to the introduction, the usual CP asymmetry by the Cabibbo mechanism is not enough to explain the matter-antimatter asymmetry in the universe. In the paper they detect a different mechanism (still explainable by Cabibbo theory but it has a larger amplitude than usual) with 5.2 standard deviations of confidence.
 
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So is that still considered within the SM or is that outside of the SM?
 
Dale said:
So is that still considered within the SM or is that outside of the SM?
It says that is hard to tell, because calculating the terms that they need is not easy (it is a challenging chromodynamics calculation).
 
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Thanks, I will be interested to see how that settles out.
 
Dale said:
Was this a prediction of the standard model
The SM predicts CP violation in certain quark processes, which includes both mesons and baryons. As far as I can tell from the paper, these new results don't rule out the possibility of other physics being involved beyond the SM, but they don't show any definite signs of such physics either.
 
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why is CP violation in baryons so small compared to mesons? paradox?
 

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