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Deviation from Standard Model observed at LHCb (B->K* mu mu)

  1. Aug 6, 2013 #1


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    As usual, the interpretation is still unclear, but I think it is an interesting effect.

    LHCb studied the angular distributions in the decay ##B^0 \to K* \mu \mu## and presented the result at EPS2013. In one variable (called P'5) in two bins, a large deviation was found (3.7 sigma in one bin).
    As many variables and bins were studied, the probability of a random fluctuation is larger than this significance suggests - LHCb gives the total probability as .5% (2.8 sigma).
    The analysis was based on 2011 data only, 2012 data will increase the statistics by more than a factor of 3.

    LHCb talk
    Theory interpretation (based on LHCb results)
    phys.org news

    My guess: theory error (as with ##\Delta A_{CP}##), or maybe a statistical fluctuation, or some measurement error. With the full LHCb dataset (and CMS, if they can measure it as well), the measurement will become much cleaner.
    New physics would be the most amazing explanation, of course.
  2. jcsd
  3. Aug 6, 2013 #2


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    Remember that ##B_{s} \to \phi \mu \mu## has also been recently measured, and while the angular observables are "consistent" with the SM the branching ratio is measured to be half of the SM prediction. (1305.2168)
    This obviously depends on the same NP operators as well as the ## \hat{O}_{7,9,10}'## opposite chirality operators. And again, the effect of any new contribution must be to lessen the width, meaning some large interference must be in play or some internal contribution that lessens the Wilson coeffs.

    Hopefully it doesn't just go away with more statistics, though 2.8##\sigma## isn't all that large yet.
  4. Aug 6, 2013 #3


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    "The uncertainties on these predictions originating from the form factor calculations are typically of the order of 20{30%."
    As we know, theory uncertainties do not follow a Gaussian distribution.
    Still an interesting difference, I did not see that.
  5. Aug 7, 2013 #4


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    "I won’t believe this experiment until it is confirmed by theory!" -- Sir Arthur Eddington
  6. Aug 13, 2013 #5
    Here was something,

    [44] arXiv:1308.1959 [pdf, other]
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