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A Signal strength parameter (interpretation)

  1. May 13, 2016 #1

    ChrisVer

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    How can in general the signal strength parameter ##\mu## be interpreted?

    I am talking for the parameter defined in Eq.1 here and plots like the Fig.1 here:
    http://arxiv.org/abs/1507.04548

    It says that it's the ratio of the i->H->f of the observed over what's expected by the SM... is the last the cross section prediction of the Higgs or for any other background?
    Then what would the <1 or >1 indicate? I think the >1 indicate a signal excess, while the <1 indicate a signal underestimation(????)
     
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  3. May 13, 2016 #2

    mfb

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    Only Higgs. The background in data is subtracted before μ is calculated.
    A deviation from the standard model. If μ=1 gets ruled out in some channel, things get interesting.
     
  4. May 15, 2016 #3

    ChrisVer

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    Is that the case even if you have background overestimation compared to data?
     
  5. May 15, 2016 #4

    mfb

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    I'm not sure if I understand your question. If you overestimate something, you are doing something wrong and should fix it, or not use what you cannot get right.
     
  6. May 15, 2016 #5

    ChrisVer

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    Well it's not unusual to get overestimates like these [at <120 or 140GeV]:
    http://cms.web.cern.ch/sites/cms.we...ZMass_7Plus8TeV_70-180_3GeV.png?itok=k2MlxuLT
    In which case subtracting the estimates from data will result to negative values.
     
  7. May 15, 2016 #6

    mfb

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    That is (hopefully) not an overestimate, just a statistical fluctuation. Yes, estimated signal strengths can be negative. As a random example, this ATLAS note has -0.4 +- 1.1 for VH -> Vbb in table 2. Note that it is consistent with 1, the uncertainties were just very large in 2012.
     
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