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So just to be clear, this particle is not predicted by the standard model? I'm no physicist, but that seems like a huge deal.

by mojoe 11y ago

valevk 11y ago
> The fact that two separate detectors spotted it at almost exactly the same energies gives some hope, but anomalous signals such as this often show up in experiments only to later vanish back into the noisy background. Yes, it would be, if it's not background noise.
soheil 11y ago
Yes, that would not be something that the SM predicts. It needs more verification, two teams out of thousands coming up with similar results on just one occasion hardly means anything, so we'll have to wait and see.
- misthop 11y ago
  While the sentiment that is needs more verification is accurate, there are not thousands of teams in this context. ATLAS and CMS are the 2 general purpose detectors at the Large Hadron Collider - they are the only teams/detectors in the world that can detect this signal, significant or not.
gibybo 11y ago
The standard model currently has 17 particles[1]. This number has grown over time, most recently when the Higgs boson was added a few years ago. The standard model makes no claim as to how many particles there can be, what their masses should be, what spin they should have, and so on. Those are unsolved questions outside of the scope of the standard model. Instead, it uses the particles we know about to make predictions about how they behave. A new particle doesn't necessarily violate the standard model in the same way that discovering a new element wouldn't necessarily violate the periodic table. It could just expand the types of predictions that it is capable of making. It is also possible that a new particle could have properties that do violate constraints predicted by the standard model, but I don't know it well enough to know whether this particular particle does so. [1] https://upload.wikimedia.org/wikipedia/commons/0/00/Standard_Model_of_Elementary_Particles.svg https://upload.wikimedia.org/wikipedia/commons/0/00/Standard...
- soheil 11y ago
  > If it turns out to be true, the chart linked below showing the 17 known elementary particles would be expanded to show an 18th. no, actually the standard model would fundamentally break down. The math does not allow for such a heavy particle. No charts could save it.
  - gibybo 11y ago
    How would it fundamentally break down? Admittedly I don't know enough to know how a particle with these particular properties would affect it, I was just trying to make the point that a new particle doesn't necessarily break the standard model. I'll try to edit my post for more accuracy.
    - claudius 11y ago
      (It's been a while since I took this class, the following might well be wrong or grossly inaccurate) The particles of the standard model are assumed to correspond to the irreducible representations (irrep) of the groups associated to the symmetries of the strong, weak and electromagnetic interactions. These groups are SU(3) (strong) and SU(2)×U(1) electroweak. The currently known particles correspond to the first few irreps of these groups, with the dimensionality of the irrep nicely matching the number of “similar” particles, see e.g. [1]. This means that, if the above assumptions hold, finding a single new particle requires there to be yet another irrep[2] which would imply that there are even more new particles corresponding to the other dimensions of this irrep. [1] https://en.wikipedia.org/wiki/Standard_Model_%28mathematical_formulation%29#Field_content_in_detail https://en.wikipedia.org/wiki/Standard_Model_%28mathematical... [2] If this is even possible, I’m not quite sure, but SUSY does something similar I guess.
  - cshimmin 11y ago
    That's not really the case. The standard model would need to be extended, sure (as the 750 GeV particle isn't predicted by the current SM). But there's no fundamental reason this can't be done; in fact in the weeks following this announcement by ATLAS/CMS, there were literally hundreds of theory models posted to the arXiv, claiming to extend the SM to account for the (potential) new resonance.
ssivark 11y ago
Yes, the Standard Model would be completely oblivious to this particle. If this turns out to be a new particle, this would be the first concrete detection of physics beyond the Standard Model. EDIT: Fair point below by @InclinedPlain. Neutrino oscilations were the first signal, but that does not motivate a radical extension like this evidence might. Needless to say, most particle physicists are excited -- but we need to hold our horses -- this does not have a sufficient p-value to warrant the status of a confirmed detection -- such statistical fluctuations come and go once in a while. Also, recent "inside" news seems to indicate that there might not be any new updates till later in the summer (rather than what the last paragraph indicates).
- InclinedPlane 11y ago
  Not exactly true. The detection of neutrino oscillations was concrete evidence of physics beyond the Standard Model. Though the consensus has been that only slight modifications of the Standard Model are needed to allow for such oscillations (and neutrino masses).
- daveguy 11y ago
  Oh good! A particle physicist. I was looking for the current p-value in the article, but couldn't find it. Do you know what it is currently compared to what is required (something like 1E-6 or 1E-9)??
  - dukwon 11y ago
    CMS observes the peak with a global significance of 1.2σ http://cds.cern.ch/record/2114808 http://cds.cern.ch/record/2114808 ATLAS observes the peak with a global significance of 2σ http://cds.cern.ch/record/2114853 http://cds.cern.ch/record/2114853 5σ is the gold standard for a discovery
    - pc86 11y ago
      Is it true that 2σ holds some significance? I imagine if it was common to get erroneous 2σ or 3σ readings this wouldn't have made the news in the way that it did. Just trying to determine if this is closer to "this is probably something but we will need to confirm" or "something weird happened but it's probably nothing"

So just to be clear, this particle is not predicted by the standard model? I'm no physicist, but that seems like a huge deal.

by mojoe 11y ago

So just to be clear, this particle is not predicted by the standard model? I'm no physicist, but that seems like a huge deal.

valevk 11y ago

> The fact that two separate detectors spotted it at almost exactly the same energies gives some hope, but anomalous signals such as this often show up in experiments only to later vanish back into the noisy background. Yes, it would be, if it's not background noise.

soheil 11y ago

Yes, that would not be something that the SM predicts. It needs more verification, two teams out of thousands coming up with similar results on just one occasion hardly means anything, so we'll have to wait and see.

misthop 11y ago
While the sentiment that is needs more verification is accurate, there are not thousands of teams in this context. ATLAS and CMS are the 2 general purpose detectors at the Large Hadron Collider - they are the only teams/detectors in the world that can detect this signal, significant or not.

gibybo 11y ago

The standard model currently has 17 particles[1]. This number has grown over time, most recently when the Higgs boson was added a few years ago. The standard model makes no claim as to how many particles there can be, what their masses should be, what spin they should have, and so on. Those are unsolved questions outside of the scope of the standard model. Instead, it uses the particles we know about to make predictions about how they behave. A new particle doesn't necessarily violate the standard model in the same way that discovering a new element wouldn't necessarily violate the periodic table. It could just expand the types of predictions that it is capable of making. It is also possible that a new particle could have properties that do violate constraints predicted by the standard model, but I don't know it well enough to know whether this particular particle does so. [1] https://upload.wikimedia.org/wikipedia/commons/0/00/Standard_Model_of_Elementary_Particles.svg https://upload.wikimedia.org/wikipedia/commons/0/00/Standard...

soheil 11y ago
> If it turns out to be true, the chart linked below showing the 17 known elementary particles would be expanded to show an 18th. no, actually the standard model would fundamentally break down. The math does not allow for such a heavy particle. No charts could save it.
- gibybo 11y ago
  How would it fundamentally break down? Admittedly I don't know enough to know how a particle with these particular properties would affect it, I was just trying to make the point that a new particle doesn't necessarily break the standard model. I'll try to edit my post for more accuracy.
  - claudius 11y ago
    (It's been a while since I took this class, the following might well be wrong or grossly inaccurate) The particles of the standard model are assumed to correspond to the irreducible representations (irrep) of the groups associated to the symmetries of the strong, weak and electromagnetic interactions. These groups are SU(3) (strong) and SU(2)×U(1) electroweak. The currently known particles correspond to the first few irreps of these groups, with the dimensionality of the irrep nicely matching the number of “similar” particles, see e.g. [1]. This means that, if the above assumptions hold, finding a single new particle requires there to be yet another irrep[2] which would imply that there are even more new particles corresponding to the other dimensions of this irrep. [1] https://en.wikipedia.org/wiki/Standard_Model_%28mathematical_formulation%29#Field_content_in_detail https://en.wikipedia.org/wiki/Standard_Model_%28mathematical... [2] If this is even possible, I’m not quite sure, but SUSY does something similar I guess.
- cshimmin 11y ago
  That's not really the case. The standard model would need to be extended, sure (as the 750 GeV particle isn't predicted by the current SM). But there's no fundamental reason this can't be done; in fact in the weeks following this announcement by ATLAS/CMS, there were literally hundreds of theory models posted to the arXiv, claiming to extend the SM to account for the (potential) new resonance.

ssivark 11y ago

Yes, the Standard Model would be completely oblivious to this particle. If this turns out to be a new particle, this would be the first concrete detection of physics beyond the Standard Model. EDIT: Fair point below by @InclinedPlain. Neutrino oscilations were the first signal, but that does not motivate a radical extension like this evidence might. Needless to say, most particle physicists are excited -- but we need to hold our horses -- this does not have a sufficient p-value to warrant the status of a confirmed detection -- such statistical fluctuations come and go once in a while. Also, recent "inside" news seems to indicate that there might not be any new updates till later in the summer (rather than what the last paragraph indicates).

InclinedPlane 11y ago
Not exactly true. The detection of neutrino oscillations was concrete evidence of physics beyond the Standard Model. Though the consensus has been that only slight modifications of the Standard Model are needed to allow for such oscillations (and neutrino masses).
daveguy 11y ago
Oh good! A particle physicist. I was looking for the current p-value in the article, but couldn't find it. Do you know what it is currently compared to what is required (something like 1E-6 or 1E-9)??
- dukwon 11y ago
  CMS observes the peak with a global significance of 1.2σ http://cds.cern.ch/record/2114808 http://cds.cern.ch/record/2114808 ATLAS observes the peak with a global significance of 2σ http://cds.cern.ch/record/2114853 http://cds.cern.ch/record/2114853 5σ is the gold standard for a discovery
  - pc86 11y ago
    Is it true that 2σ holds some significance? I imagine if it was common to get erroneous 2σ or 3σ readings this wouldn't have made the news in the way that it did. Just trying to determine if this is closer to "this is probably something but we will need to confirm" or "something weird happened but it's probably nothing"