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Sigma for an observable

  1. Mar 30, 2015 #1
    Hi all,

    I'd like to understand what does it mean by allowed 1 or 2 ## \sigma ## regions for some observable, like R(D) in Fig. 1 left [ 1206.2634v2] ?

    And how can I calculate or plot this value or region according to any theoritical model ..

  2. jcsd
  3. Mar 30, 2015 #2


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    Standard deviations have to do with experimental precision. It is not something you derive from the theoretical model.

    If a parameter set is within the ##1\sigma## region, it means that if reality is described by the theory and with those particular parameter values, then the result is within the 68% least extreme outcomes you could have found in the experiment. For all parameter sets outside of the allowed ##1\sigma## region, the results are among the 32% most extreme results given those parameters and the parameter set is rejected at ##1\sigma## (or "at the 68% confidence level").

    Footnote: This naturally requires you to define what you mean by an outcome being extreme.
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