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Lepton Universality In Question, a Standard Model Assumption 62

Posted by Soulskill
from the we'ere-slightly-more-wrong-than-we-thought dept.
Charliemopps writes: "Over the past few years, more and more experiments have started to question one of the core assumptions of the standard model: Lepton Universality. Simply put, the weak nuclear force is assumed to work equally on all Leptons (electron, muon and tau). Two years ago The Babar experimental collaboration reported that measurements indicated this may not have been the case. But the measurements were not accurate enough to be definitive.

Now, a report from The LHC shows that they have analyzed their entire dataset of proton-proton collisions and found a rather large discrepancy. These measurements are still not all that accurate. These decays happen so rarely that even with this huge data set there is still about a 1% change they are incorrect. One explanation for such measurements is an as-yet-undiscovered, charged Higgs particle. It would have to be extremely heavy: greater than 109GeV possibly even as high as 150GeV. This is predicted by some models outside of the Standard Model, like Supersymmetry."
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Lepton Universality In Question, a Standard Model Assumption

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  • No Problem: (Score:5, Funny)

    by Tablizer (95088) on Wednesday June 04, 2014 @05:44PM (#47167657) Homepage Journal

    To "fix" it, just add one or more of the following to the model:

    * More turtles
    * More nested epicycles
    * More dimensions
    * Invent dark [something] to plug it
    * Say God did it

    Profit!

    • Re: (Score:1, Funny)

      by Anonymous Coward
      We can invent a dark, energy-less, massless particle that travels backwards in time and only interacts with other particles on Tuesday afternoons. Got to keep propping up the standard "model".
    • Re:No Problem: (Score:5, Insightful)

      by Anonymous Coward on Wednesday June 04, 2014 @09:18PM (#47168685)
      Just remember if you propose a new thoery that can explain the data and make quantitative, it still needs to past the most important test: the gut instinct of forum posters on the internet. They seem to act like science shouldn't propose new theories when new data conflicts with old theories... or insist new theories are ok, except for the ones they don't like.
  • But... (Score:5, Informative)

    by Stormy Dragon (800799) on Wednesday June 04, 2014 @06:24PM (#47167833) Homepage

    This is predicted by some models outside of the Standard Model, like Supersymmetry.

    Except that that LHC's ongoing failure to find any SUSY particles is making it increasingly unlikely Supersymmetry is right either:

    http://scienceblogs.com/starts... [scienceblogs.com]

    • Re:But... (Score:5, Informative)

      by jfengel (409917) on Wednesday June 04, 2014 @06:49PM (#47167935) Homepage Journal

      The data go a long way to ruling out the Minimal Supersymetric Standard Model (MSSM), but other SUSY theories are still in the running. The MSSM has the advantage of being, well, minimal, but there's no special reason to expect the universe to have made it that easy on us.

      It's hard to say which theory this points us to, if any, but the Two Higgs Doublet Model (2HDM) is a part of several. Those theories will help refine what kind of data to look for and what kinds of experiments to configure.

      • Yes, but as I understand it, the whole point of supersymmetry was to solve the Hierarchy problems. Even if one of those other variants of supersymmetry holds, they would do so at an energy too high to still resolve the hierarchy problem. So the question becomes what the point of them is, other than having supersymmetry purely for the sake of having supersymmetry.

      • by Pausanias (681077)

        Let's face it---supersymmetry's entire cachet is based on the minimal supersymmetric standard model. If the minimal model goes away, it will lose so many supporters that it will become yet another one of "those" theories that few (other than its proponents) care about.

    • by Anonymous Coward on Wednesday June 04, 2014 @06:58PM (#47168007)

      With regards to Supersymmetry I have the feeling the LHC is going to end up being this century's version of Michelson-Morley.

      However, given what happened after Michelson-Morley, we may be in for some very exciting new physics in the years to come if we can disprove Supersymmetry.

      (At least I hope we are... :-))

      • by jandersen (462034)

        I think this is what we all hope - that the existing theories may finally be proven wrong. To a scientist, it is always the unsolved problems that are interesting; the journey and the fun is over when you reach your goal.

        I'm not sure about Supersymmetry, though - it's only intuition, but my feeling is that it should have been a minimal form of Supersymmetry, if any. Occam's Razor and all that - I believe Einstein once used the expression 'As simple as possible, but no simpler than that'. I think the next bi

      • What on Earth would make you say that? I see no similarities between this experiment and the Michelson-Morley experiment.
        • It's true, physically it's a very different experiment. However, I think what the poster was referring to was what Michelson-Morley led to, which was huge. From Wikipedia:

          It attempted to detect the relative motion of matter through the stationary luminiferous aether ("aether wind"). The negative results are generally considered to be the first strong evidence against the then prevalent aether theory, and initiated a line of research that eventually led to special relativity, in which the stationary aether concept has no role. The experiment has been referred to as "the moving-off point for the theoretical aspects of the Second Scientific Revolution".

          In other words, although the aims of Michelson-Morley were proved wrong, what they did find eventually led to big new science - and the same might apply here once hindsight is brought to bear.

  • by Anonymous Coward

    Change you can believe in!

    "chance", you idiots!!!

  • by Trogre (513942) on Wednesday June 04, 2014 @10:01PM (#47168875) Homepage

    When I grow up I'm going to Lepton University!

    No wait...

  • As I could not find it on the arXiv (http://xxx.lanl.gov/), nor inspire (http://inspirehep.net) nor any official statement from CERN I assume this is just a preliminary result so far. Even as such I would expect some kind of estimate on the systematic uncertainties which go with this measurement. Without that it is not particularly relevant yet as those uncertainties could be substantial. So at the moment it is premature to talk about a discrepancy with the standard model (nor the previous measurements).
  • Is there really a 1% probability that they are incorrect or is there a 1% to get such data if they were wrong?
  • Honestly.. a 2.6 sigma result? History is littered with 3 sigma results that vanish as more data is taken and detectors and other experimental hardware/software become better understood and modeled.

    • Yes, but this isn't the only result. There have been many over the past 10yrs. None are definitive, but they all seem to agree. That's hard to swallow as a random statistical anomaly. Don't get me wrong, it still could be... But it's worth our interest.

  • I read the headline as "Lepton University"

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