LHCb Discovers Two New Particles

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Discussion Overview

The discussion revolves around the recent discovery of two new particles by the LHCb experiment, focusing on their implications for the strong interaction and the broader context of particle physics. Participants explore the significance of these findings in relation to existing theories, particularly quantum chromodynamics (QCD), and the nature of the particles themselves.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants express excitement about the discovery, questioning what it implies about the strong interaction.
  • Others note that the B hadrons were expected and suggest that while their masses may provide insights, the findings are not unexpected.
  • A participant highlights the significance of the ##Z_c^-(4100)## hint, mentioning that it is based on limited data and anticipates further updates with more statistics.
  • Concerns are raised about the lengthy process of publishing the findings, with some suggesting that the collaboration may be stretched thin, impacting the speed of analysis and publication.
  • Some argue that the discoveries confirm existing theories rather than providing new insights, stating that it would have been more significant if particles not predicted by current theory had been found.
  • There is discussion about the nature of the ##Z_c(4100)## particle, with some suggesting it could be a hadron molecule or a tetraquark/pentaquark, but noting that its internal structure remains unresolved.

Areas of Agreement / Disagreement

Participants generally agree that the discoveries confirm existing theoretical predictions, but there is disagreement regarding the significance of these findings and the implications for future research. The discussion remains unresolved on the broader impact of these discoveries on the field of particle physics.

Contextual Notes

Some participants mention that the analysis of the discovered particles has not been the primary focus for the researchers involved, and there are concerns about the collaboration's capacity to handle ongoing analyses. The significance of the ##Z_c(4100)## particle is also noted to be based on limited data, raising questions about its reliability.

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Very cool. Thanks for posting.
 
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Wow. Thank you.
 
The B hadrons were expected to exist. Nice to see them and some theorists will learn something from their mass, but nothing unexpected.
The ##Z_c^-(4100)## hint is interesting. It is based on about half the recorded data, so we will probably get an update with more statistics soon.

It is interesting to see how LHCb announces the discoveries of these particles. They quote a significance of 12.6σ based on 3/fb integrated luminosity from Run 1 (2011/2012). The selection is nothing fancy and similar to many other analyses. A peak that prominent is really easy to find, a bachelor student could have found the particles in 2013 - and there is a good chance someone did see them that early. LHCb could have made a quick conference note about them, but they decided to directly write a full paper about them, which takes much more time. There are no other experiments that could find these particles, so they were not in a hurry. The long delay still indicates that there are not so many people working on it.
This is not the first time new particles pop up with huge significances - and not necessarily the last. How many more hadrons did LHCb find where the analysis is still ongoing?
 
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mfb said:
The B hadrons were expected to exist. Nice to see them and some theorists will learn something from their mass, but nothing unexpected.
The ##Z_c^-(4100)## hint is interesting. It is based on about half the recorded data, so we will probably get an update with more statistics soon.

It is interesting to see how LHCb announces the discoveries of these particles. They quote a significance of 12.6σ based on 3/fb integrated luminosity from Run 1 (2011/2012). The selection is nothing fancy and similar to many other analyses. A peak that prominent is really easy to find, a bachelor student could have found the particles in 2013 - and there is a good chance someone did see them that early. LHCb could have made a quick conference note about them, but they decided to directly write a full paper about them, which takes much more time. There are no other experiments that could find these particles, so they were not in a hurry. The long delay still indicates that there are not so many people working on it.
This is not the first time new particles pop up with huge significances - and not necessarily the last. How many more hadrons did LHCb find where the analysis is still ongoing?
I was wondering why no one else besides them was making a big deal out of this discovery. Now it makes sense; it's not a huge deal in general (according to you).
 
mfb said:
A peak that prominent is really easy to find, a bachelor student could have found the particles in 2013 - and there is a good chance someone did see them that early. LHCb could have made a quick conference note about them, but they decided to directly write a full paper about them, which takes much more time. There are no other experiments that could find these particles, so they were not in a hurry. The long delay still indicates that there are not so many people working on it.

I like this interpretation; it sounds rather noble.

The analysis had 2 people working on it, and it wasn't the primary project for either of them. It went into review in 2015 and it kind of petered out until some renewed effort earlier this year. It wasn't a conscious decision. The collaboration is stretched quite thinly, and sometimes things like this slip through the cracks.

By the way, the procedure for conference notes within LHCb really discourages writing them: to go conference note then paper adds so much overhead that most things go straight to paper because it's less effort.
 
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Amrator said:
I was wondering why no one else besides them was making a big deal out of this discovery. Now it makes sense; it's not a huge deal in general (according to you).
It would have been a big deal if they had discovered particles not already predicted by current theory so that physicists would have a new clue in how to modify the Standard Model. But these detections essentially say, "yup, the theory still works."
 
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vela said:
It would have been a big deal if they had discovered particles not already predicted by current theory so that physicists would have a new clue in how to modify the Standard Model. But these detections essentially say, "yup, the theory still works."
What they're really saying is "yup, our accelerator is still useful." And it is.
 
Amrator said:
https://home.cern/about/updates/2018/09/lhcb-experiment-discovers-two-perhaps-three-new-particles
http://lhcb-public.web.cern.ch/lhcb-public/Welcome.html#LHCCCKM

This is very exciting news! What exactly does it say about the strong interaction?

The sigma 6097 particles simply confirm longstanding QCD predictions. Not ground breaking but confirming pre-existing predictions of pre-existing theories is always a good thing.

The Zc(4100) adds to a menagerie of particles whose proper name is unresolved because we're not sure about the internal structure of the compound particle. It adds to a shed full of inconclusively characterized hadrons that are awaiting a more definitive interpretation (and at 3 sigma, it could be a fluke although there is no good reason to think so). Lots of these could end up being 'hadron molecules" and some could end up being true tetraquarks and pentaquarks.
 
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Fantastic!
 

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