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Higgs production cross section

  1. Jan 31, 2016 #1
    Hi all,

    I try to find the exact calculated gluon- gluon fusion cross section for the SM- Higgs with mass 125 GeV, for instance at CME = 14 TeV.

    I found on twiki page:
    " https://twiki.cern.ch/twiki/bin/view/LHCPhysics/CERNYellowReportPageAt1314TeV#s_14_0_TeV [Broken]"

    ##\sigma(gg \to h) = 49.47~ pb##

    while in reference like "arXiv:hep-ph/0503172 ", table(3.2):

    ##\sigma(gg \to h) \sim 37 ~ pb##

    Both calculations are NLO, but why there is this difference ?
     
    Last edited by a moderator: May 7, 2017
  2. jcsd
  3. Jan 31, 2016 #2

    mfb

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    The first one is NNLO QCD. For electroweak processes it is just NLO but those should be a small contribution. The NLO calculation discusses some NNLO effects but I don't understand what exactly they do.
     
  4. Jan 31, 2016 #3
    So I wonder can we calculate ## \sigma (gg \to h) ## at LO or NLO like in " arXiv:hep-ph/0503172 ",

    while take the uncertainties (the standard deviation ) from NNLO calculations ?

    The following paper " arXiv:1206.5047 [hep-ph]" made that in Fig. (1). While they use LO formula for the production cross section Equ. (5), they cite the Cern twiki page for ## \sigma1~ \mbox{and}~ \sigma2 ##,

    is this consistent to take the uncertainty from NNLO calculation for a cross section calculated at LO?
     
    Last edited: Jan 31, 2016
  5. Jan 31, 2016 #4

    Vanadium 50

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    Virtually nothing that is done is consistent. Your choice is a) the latest calculations, or b) a consistent set of calculations. Most people choose a).

    For Higgs production, the state of the art is N3LO, Anastasiou et al. PRL 114, 212001 (2015)
     
  6. Jan 31, 2016 #5
    Hi,

    I added my last sentence :) , I hope it's clear enough.
     
  7. Feb 1, 2016 #6

    mfb

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    Here is the NNNLO calculation. They also compare LO, NLO, NNLO and NNNLO in figure 2. The difference between NLO and NNLO is ~10/pb, although both still show significant scale-dependence. NNNLO is significantly better in terms of scale-dependence. Note that the plot is for 13 TeV. Figure 3 includes 14 TeV bands, the same difference is visible there.

    I don't understand how you would take a NNLO calculation for a LO uncertainty. Where is the point in having an uncertainty on LO if you have a NNLO calculation?
     
  8. Feb 1, 2016 #7
    It's this paper " arXiv:1206.5047 [hep-ph]", as you see for Fig. (1), they take the uncertainty 14.7 % from [10] , which are NNLO. While they use LO formula, ( Equ.5 )for the new physics ( NP) ## gg \to h ## cross section.

    Even I don't know in Fig. (1), when they normalized ## \sigma_{NP} ## by ## \sigma_{SM} ## which value for ## \sigma_{SM} ## they considered, did they calculate it at LO or they just take [10] value .
     
  9. Feb 1, 2016 #8

    mfb

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    Those are different things.
    As far as I understand it, they compare the cross-section for (LO NP + NNLO SM) with (NNLO SM), and use the NNLO SM uncertainty (which is independent of new physics) as comparison: if the NP prediction is within the uncertainties of the SM calculation, the cross-section alone is not sufficient to see new physics.
     
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