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Featured I LHCb Discovers Two New Particles

  1. Sep 27, 2018 #1
    Last edited: Sep 27, 2018
  2. jcsd
  3. Sep 27, 2018 #2


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    Very cool. Thanks for posting.
  4. Sep 27, 2018 #3


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    Wow. Thank you.
  5. Sep 27, 2018 #4


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    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?
  6. Sep 27, 2018 #5
    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).
  7. Sep 28, 2018 #6


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    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.
  8. Sep 29, 2018 #7


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    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."
  9. Sep 29, 2018 #8


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    What they're really saying is "yup, our accelerator is still useful." And it is.
  10. Oct 2, 2018 #9


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    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.
  11. Oct 2, 2018 #10
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