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A Qt-subtraction formalism

  1. Nov 17, 2016 #1
    As i know the qt-subtraction formalism is a method to cancel IR divergences, for example in small diphoton transverse momentum . nevertheless I can't understand why the prediction of 2gnnlo in https://arxiv.org/abs/1301.4536 diverges in region of small diphoton transverse momentum (qt) .
    thank you in advance.
     
  2. jcsd
  3. Nov 17, 2016 #2

    ChrisVer

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    are you refering to Fig.1b?
     
  4. Nov 17, 2016 #3
    yes
     
  5. Nov 17, 2016 #4

    ChrisVer

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    So, I am not sure I understand your question though... 2gNNLO prediction seems to be far off the data by 2-3 stds in the whole diphoton pT spectrum? At least compared to SHERPA
     
  6. Nov 17, 2016 #5
    I think i understand the answer. qt-subtraction formalism is like phase "phase space slicing" formalism suitable for reaction like 1+2->3+4+5 ,that was explained in http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.344.8809&rep=rep1&type=pdf where 3 and 4 have high pt and 5 can be soft or collinear. whereas singularity related to qt->0 originated from 1+2->3+4 processes, consequently for this region of phase space we need soft gluon resummation.
     
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