7 ms·

I assume these particles were already predicted as part of the Standard Model?

gpderetta 10y ago
yes, and note that these are not fundamental particles (like the Higgs was for example), but composite particles of yet another combination of the fundamental quarks. The SM predicts the existence of hundreds (thousands?) of these.
- inlineint 10y ago
  Actually it is even a one new particle (Omega_c baryon), but they observed five different excited energy states of it (like observing different excited states of a Hydrogen atom), so called resonances [1]. But the discovery is still exciting because it should have been really hard to find something that we don't really know how looks like in such large amount of noise. The problem is that it is hard for us to predict masses/energies of new composite particles because although Standard Model provides hypothetical way to do it, it is infeasible computationally. [1] http://physics.stackexchange.com/questions/64862/resonances-in-high-energy-physics http://physics.stackexchange.com/questions/64862/resonances-...
  - nonbel 10y ago
    >"it should have been really hard to find something that we don't really know how looks like in such large amount of noise." But if there are thousands of different such "surprising-to find-particles" to possibly detect, is it actually surprising to observe one of them? Edit: Also, from the top answer at your link: "The first generation of elementary particles are by observation not composite and therefore not seen to decay...The Standard Model of elementary particles, with the three generations of matter, gauge bosons in the fourth column and the Higgs boson in the fifth." From wikipedia: "In the Standard Model, the Higgs particle is a boson with no spin, electric charge, or colour charge. It is also very unstable, decaying into other particles almost immediately." https://en.wikipedia.org/wiki/Higgs_boson https://en.wikipedia.org/wiki/Higgs_boson So do elementary particles decay or not?
    - inlineint 10y ago
      > But if there are thousands of different such "surprising-to find-particles" to possibly detect, is it actually surprising to observe one of them? It is hard to correctly identify what exactly particles from those possible thousands are observed in given data. The are two main problems: the properties of those not yet observed particles are not well known (because it is computationally hard to predict them from the standard model) and because the number of useful events is much much smaller than the number of events that correspond to already known events. > So do elementary particles decay or not? I don't see a contradiction here: the first generation of elementary particles does not decay (or has not been observed to decay yet), Higgs boson is not from then because the author of the answer are talking about the first generation of fermions and Higgs boson is not one of them.
      - nonbel 10y ago
        Thanks, I missed that "first generation" detail.
brutuscat 10y ago
Professor Tim Gershon, Professor of Physics at University of Warwick and UK spokesperson for the LHCb experiment: “After the LHCb experiment is upgraded in the next long shutdown of the LHC (during 2019-20), it will be able to move to the next stage in the search for new particles: namely, doubly heavy baryons. These states – which contain two charm quarks or two beauty quarks or one of each – have long been predicted, but never yet observed. Their discovery will help to address important unsolved questions about how hadrons are bound together by the strong interaction.” So I would assume that yes they have been predicted and is opening the doors for further confirmations?
- wolfgke 10y ago
  > Their discovery will help to address important unsolved questions about how hadrons are bound together by the strong interaction. If the particles were already predicted by the standard model, what kind of unsolved questions are to address here, besides validating the predictions of the standard model even further? (serious question)
  - binarymax 10y ago
    Because a prediction is just an assumption (theory), and it can become a house of cards when basing future science on that assumption. Observation is proof, so future science can use that proof without worry.
    - nonbel 10y ago
      Can you clarify? In my mind "prediction" != "assumption" != "theory" and "observation" != "proof" Basically I seem to disagree with everything you wrote.
      - herpdorplarp 10y ago
        By assuming validity of a theory you can make predictions. Observations provide evidence in support of this.
guitarbill 10y ago
AFAIK, the experimentally determined rest masses of these excited states/particles (same thing, different was of looking at it) agree with the calculated ones well. So yes, they were predicted. No surprises sadly; of course it's still a huge achievement!
- dukwon 10y ago
  The theory uncertainties are large. Any measurements within a broad range would also agree with some calculated masses. That doesn't tell you much. See e.g. https://arxiv.org/abs/1311.4806 https://arxiv.org/abs/1311.4806
sidlls 10y ago
Yes, but these experiments serve at least three purposes. One, to verify the Model (after all, if its predictions fail in some part it will have to be revised). Another, to verify the characteristics of the predicted particles (there might be some differences from the prediction that are important, but not hypothesis-breaking). Finally, however unlikely and yet most excitingly (to me at least), to open new avenues of questioning and hypothesis up by really throwing into question some things.
- M_Grey 10y ago
  It's worth remembering that the Higgs particle was also predicted by the standard model, and no one underestimates the importance of that confirmation.
  - cynicalkane 10y ago
    Not in the same way. There was no experimental evidence for the Higgs field before the Higgs was observed. These new particles arise naturally out of parts of the Standard Model that are already experimentally tested.
    - M_Grey 10y ago
      You're not wrong, but you'd have been really hard-pressed to find someone of significance who didn't already believe the Higgs mechanism was there. In the sense that mass exists, there was a high degree of expectation there too. It's actually quite amazing to have so many of these recent discoveries, also be confirmations. It's been over a century of this, starting with Relativity.
  - whyever 10y ago
    The Higgs is an elementary particle, so its discovery was much more exciting. There are a lot of particles made up of quarks, like the five mentioned in the article: http://pdg.lbl.gov/2016/tables/rpp2016-qtab-mesons.pdf http://pdg.lbl.gov/2016/tables/rpp2016-qtab-mesons.pdf http://pdg.lbl.gov/2016/tables/rpp2016-qtab-baryons.pdf http://pdg.lbl.gov/2016/tables/rpp2016-qtab-baryons.pdf
ajross 10y ago
Yes. They're baryons (three-quark states). This is analogous to the discovery/synthesis of new isotopes in the middle of the last century. Technically they were "predicted", but it's still important to take the measurements. Occasionally there are surprises.
deleted 10y ago
[deleted]

yes, and note that these are not fundamental particles (like the Higgs was for example), but composite particles of yet another combination of the fundamental quarks. The SM predicts the existence of hundreds (thousands?) of these.

inlineint 10y ago
Actually it is even a one new particle (Omega_c baryon), but they observed five different excited energy states of it (like observing different excited states of a Hydrogen atom), so called resonances [1]. But the discovery is still exciting because it should have been really hard to find something that we don't really know how looks like in such large amount of noise. The problem is that it is hard for us to predict masses/energies of new composite particles because although Standard Model provides hypothetical way to do it, it is infeasible computationally. [1] http://physics.stackexchange.com/questions/64862/resonances-in-high-energy-physics http://physics.stackexchange.com/questions/64862/resonances-...
- nonbel 10y ago
  >"it should have been really hard to find something that we don't really know how looks like in such large amount of noise." But if there are thousands of different such "surprising-to find-particles" to possibly detect, is it actually surprising to observe one of them? Edit: Also, from the top answer at your link: "The first generation of elementary particles are by observation not composite and therefore not seen to decay...The Standard Model of elementary particles, with the three generations of matter, gauge bosons in the fourth column and the Higgs boson in the fifth." From wikipedia: "In the Standard Model, the Higgs particle is a boson with no spin, electric charge, or colour charge. It is also very unstable, decaying into other particles almost immediately." https://en.wikipedia.org/wiki/Higgs_boson https://en.wikipedia.org/wiki/Higgs_boson So do elementary particles decay or not?
  - inlineint 10y ago
    > But if there are thousands of different such "surprising-to find-particles" to possibly detect, is it actually surprising to observe one of them? It is hard to correctly identify what exactly particles from those possible thousands are observed in given data. The are two main problems: the properties of those not yet observed particles are not well known (because it is computationally hard to predict them from the standard model) and because the number of useful events is much much smaller than the number of events that correspond to already known events. > So do elementary particles decay or not? I don't see a contradiction here: the first generation of elementary particles does not decay (or has not been observed to decay yet), Higgs boson is not from then because the author of the answer are talking about the first generation of fermions and Higgs boson is not one of them.
    - nonbel 10y ago
      Thanks, I missed that "first generation" detail.

brutuscat 10y ago

Professor Tim Gershon, Professor of Physics at University of Warwick and UK spokesperson for the LHCb experiment: “After the LHCb experiment is upgraded in the next long shutdown of the LHC (during 2019-20), it will be able to move to the next stage in the search for new particles: namely, doubly heavy baryons. These states – which contain two charm quarks or two beauty quarks or one of each – have long been predicted, but never yet observed. Their discovery will help to address important unsolved questions about how hadrons are bound together by the strong interaction.” So I would assume that yes they have been predicted and is opening the doors for further confirmations?

wolfgke 10y ago
> Their discovery will help to address important unsolved questions about how hadrons are bound together by the strong interaction. If the particles were already predicted by the standard model, what kind of unsolved questions are to address here, besides validating the predictions of the standard model even further? (serious question)
- binarymax 10y ago
  Because a prediction is just an assumption (theory), and it can become a house of cards when basing future science on that assumption. Observation is proof, so future science can use that proof without worry.
  - nonbel 10y ago
    Can you clarify? In my mind "prediction" != "assumption" != "theory" and "observation" != "proof" Basically I seem to disagree with everything you wrote.
    - herpdorplarp 10y ago
      By assuming validity of a theory you can make predictions. Observations provide evidence in support of this.

guitarbill 10y ago

AFAIK, the experimentally determined rest masses of these excited states/particles (same thing, different was of looking at it) agree with the calculated ones well. So yes, they were predicted. No surprises sadly; of course it's still a huge achievement!

dukwon 10y ago
The theory uncertainties are large. Any measurements within a broad range would also agree with some calculated masses. That doesn't tell you much. See e.g. https://arxiv.org/abs/1311.4806 https://arxiv.org/abs/1311.4806

sidlls 10y ago

Yes, but these experiments serve at least three purposes. One, to verify the Model (after all, if its predictions fail in some part it will have to be revised). Another, to verify the characteristics of the predicted particles (there might be some differences from the prediction that are important, but not hypothesis-breaking). Finally, however unlikely and yet most excitingly (to me at least), to open new avenues of questioning and hypothesis up by really throwing into question some things.

M_Grey 10y ago
It's worth remembering that the Higgs particle was also predicted by the standard model, and no one underestimates the importance of that confirmation.
- cynicalkane 10y ago
  Not in the same way. There was no experimental evidence for the Higgs field before the Higgs was observed. These new particles arise naturally out of parts of the Standard Model that are already experimentally tested.
  - M_Grey 10y ago
    You're not wrong, but you'd have been really hard-pressed to find someone of significance who didn't already believe the Higgs mechanism was there. In the sense that mass exists, there was a high degree of expectation there too. It's actually quite amazing to have so many of these recent discoveries, also be confirmations. It's been over a century of this, starting with Relativity.
- whyever 10y ago
  The Higgs is an elementary particle, so its discovery was much more exciting. There are a lot of particles made up of quarks, like the five mentioned in the article: http://pdg.lbl.gov/2016/tables/rpp2016-qtab-mesons.pdf http://pdg.lbl.gov/2016/tables/rpp2016-qtab-mesons.pdf http://pdg.lbl.gov/2016/tables/rpp2016-qtab-baryons.pdf http://pdg.lbl.gov/2016/tables/rpp2016-qtab-baryons.pdf

ajross 10y ago

Yes. They're baryons (three-quark states). This is analogous to the discovery/synthesis of new isotopes in the middle of the last century. Technically they were "predicted", but it's still important to take the measurements. Occasionally there are surprises.

deleted 10y ago

[deleted]