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LHC Experiment Yields No Insight into Post-Higgs Physics

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LHC beauty, magnet, B meson

The giant magnets of the LHCb detector. Credit: CERN

A new discovery at the Large Hadron Collider near Geneva casts a shadow across a hypothetical realm of particle physics that many had hoped would be the collider’s next major exploration after the apparently successful hunt for the Higgs boson.

Physicists working with the collider’s LHC beauty, or LHCb, detector have observed a new kind of particle behavior, the researchers announced November 12 at the Hadron Collider Physics Symposium in Kyoto, Japan. The LHCb physicists have identified the very rare decay of a strange beauty particle B0s (a beauty antiquark bound to a strange quark) into two particles called muons. (A muon is a charged particle akin to a heavyweight electron.) And the new data limit the possibilities for many hypothesized extensions of the Standard Model of particle physics, including the concept of supersymmetry.

The short-lived strange beauty particle decays into other particles almost immediately after its creation in LHC collisions, but it almost never decays into a positive muon and a negative muon. The rarity of the decay makes it difficult to observe, and in fact the LHCb physicists claim that their measurements are the first solid evidence for the phenomenon. But the reigning theory of subatomic particles and forces, the Standard Model of particle physics, predicts just how often the effect should occur—about three times in a billion. Any deviation from that number would suggest the existence of new particles or forces unaccounted for by the Standard Model.

Strange beauty particle, decay, LHCb

A candidate event for a strange beauty particle decaying into two muons. Credit: CERN

The LHCb data (pdf) match up well with the Standard Model predictions of roughly three in a billion for this effect, potentially ruling out hypothetical extensions to the Standard Model that would impact the decay rate of the strange beauty particle into muons. “The detailed implications of this result will take a while to work through, but the general implication is easy to state: the Standard Model has survived another test,” physicist Matt Strassler wrote on his blog. “And the constraints from LHC data on speculative ideas that predict particles and forces beyond those of the Standard Model have become tighter.”

One of the most popular ideas that could move physics beyond the Standard Model is supersymmetry—the proposal that every elementary particle has a heavier, as-yet-unseen cousin that rounds out the particle zoo. If the strange beauty particle had decayed at an unexpected rate that the Standard Model had failed to predict, it might have provided some justification for supersymmetry. The LHC has yet to find any evidence for supersymmetric particles of any kind, and indeed some variants of supersymmetry predict a different pattern of particle decays than those now documented by LHCb. “Supersymmetry is not ruled out by our measurement, but it is strongly constrained,” LHCb spokesperson Pierluigi Campana told the CERN Bulletin, meaning that only certain flavors of supersymmetry jibe with the new data.

A BBC article framed the LHCb finding as dealing “a significant blow” to supersymmetry, but Strassler objected to that wording on his blog. “Failure to find one variant of a theory is not evidence against other variants,” he wrote. “If you’re looking for your lost keys, failing to find them in the kitchen, living room and bedroom is not evidence against their being somewhere else in the house.”

About the Author: John Matson is an associate editor at Scientific American focusing on space, physics and mathematics. Follow on Twitter @jmtsn.

The views expressed are those of the author and are not necessarily those of Scientific American.

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  1. 1. jtdwyer 8:34 pm 11/13/2012

    Re. missing evidence for supersymmetry:
    “If you’re looking for your lost keys, failing to find them in the kitchen, living room and bedroom is not evidence against their being somewhere else in the house.”

    Apparently Matt Strassler does not wish to consider that the probability of finding them anywhere in the house is diminishing…

    I suppose that if you don’t find them anywhere in the house you could always hypothesize the existence of another room – they might be in there!

    Link to this
  2. 2. Chryses 6:17 am 11/14/2012

    jtdwyer (1),

    “… Matt Strassler does not wish to consider that the probability of finding them anywhere in the house is diminishing…

    Exactly. TY.

    Link to this
  3. 3. vinodkumarsehgal 9:10 am 11/14/2012

    Possibility of appearance of some heavy supersymmetric particles at yet not achieved higher energy in the collider can not be ruled out unless those energy levels are achieved.

    Link to this
  4. 4. ottokrog 11:10 am 11/14/2012

    Last year in december the statistics on the Higss particle was 3 sigma. That is not enough to call it a scientific discovery. The July verdict was a 5 sigma, which is a close to 100 % discovery. But that 5 sigma was only that there is a particle, not on the qualities that is necessary to call it the Real Higgs particle. I don’t think that statistics on the qualities has changed much since last december, but I cannot say, because the media does not write about it.

    My prediction is still that the qualities of the Higgs particle, necessary to prove the standard model right, will not reach 5 sigma. The simple argument is that these qualities do not exist.

    The standard model in its formative states, concluded that there is no mass. That sounded weird to Peter Higgs, and therefore he mathematically predicted the Higgs particle.

    I think that the standard model is right, when it comes to the conclusion of no mass. I, as Einstein did in his older days, think that everything, including gravity, can be explained through electromagnetism. On top of that I think that above the force of electromagnetism there must be a force that we do not know, yet.

    I have a videopresentation on my blog, that explains this in details. But beware I am no physician, I am a philosopher using physics to make my point.

    Link to this
  5. 5. Zexks 1:08 pm 11/14/2012


    I think you missed this part in your accusation:
    “Strassler objected to that wording”

    In reference to:
    “a significant blow”
    A significant blow would be having searched the entire house and not found them. Not searching one room and declaring they’re not in the house.

    But it honestly sounds like you’re speaking as if they should quit all together, simply because one upon thousands of test, yet to start, came back negative. Almost as if you’d tell Einstein to give up simply because he couldn’t resolve the cosmological constant. You don’t see a news paper declaring a definitive blow to a theory simply because of the results of a single test a bit much, while never even considering the other variants of said theory, or at the very MINIMUM acknowledging other variants even exist?

    Link to this
  6. 6. basudeba 10:19 pm 11/14/2012


    One participant in the CMS Collaboration, who took part in the experiment, made a presentation, in which he declared that the team found 4 leptons of mass 129 GeV. This has not been reported in the media.

    Till now no one has conclusively and unambiguously declared that the Higg’s particle exists and has been discovered. We suspect the whole hullabaloo was to get more funds, which is evident from subsequent developments.

    Link to this

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