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====== Discussion on Differential Higgs Cross Section Measurements ======

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== Session 1 discussion ==

  * Discussion focused on H->gammagamma and H->4leptons (and H->WW)

  * Currently available measurements:
    * ATLAS H->gammagamma: http://arxiv.org/abs/1407.4222 (https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HIGG-2013-10/)
    * ATLAS H->4leptons: http://arxiv.org/abs/1408.3226 (https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HIGG-2013-22)
    * ATLAS combination of H->gammagamma and H->4leptons: http://arxiv.org/abs/1504.05833 (https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HIGG-2014-11/)
    * Results from CMS will hopefully be available soon.
    * //[Update]// Several talks with details on current and planned measurements were presented at the LHC Higgs XS WG kick-off meeting on fiducial cross sections: https://indico.cern.ch/event/399923/

  * What would be other useful observables and/or corners of phase space that are not currently measured by the experiments?
        * Inclusive variables
                * pT with a finer binning especially in the low pT range once possible 
                * phi* probes the low pT phase space region in a different way (experimental resolution should be better for H->4leptons; H->gammagamma to be checked)
                * pTt (redundant with phi*, check which one can be measured better)
        * 0-jet resolution variables (currently measured: pTj, TauCj)
                * Tau(C)j (lower pTj cut important)
                * Tau0
        * 1-jet resolution variables for pTj1/pT(H)/Tauj1 > cut for different cuts (30, 50, 100)
                * pTj1/pTj2 more differentially 
                * pT(Hj-system)
                * phi(H-j)
                * Tau1, jetmass
        * 2-jet: CP studies with ggH
                * Delta phijj mapped to full [0, 2pi] (see arXiv:1006.0986)
                * for CP studies in ggH: use loose delta eta_jj cut (some separation between jets, but looser than one would use for VBF studies)
        * While statistics is limited, measurement of the 1st, 2nd moments of distributions is useful\\ (binning effects should be investigated).


  * H->WW(->lnulnu)
    * Most promising: 0-jet (smaller uncertainties from ttbar backgrounds)
    * Definition of fiducial region should include cuts on mll and mT
      *mT<mH reduces off-shell component to avoid associated uncertainties (~10%)
    * Interesting measurement: 0-jet cross section as a function of the pT cut in the jet veto, going as low as possible
    * Do not subtract pp->WW contribution to avoid associated uncertainties (quote estimated contribution)
    * Harmonized fiducial cross section measurements between Higgs and SM would be nice


  * Possibility of a measurement of VH?
    * high pT(V) (easier experimentally) or m(VH) (more direct from the theory perspective) would be interesting from the BSM perspective
    * H->bbbar 0-jet selection is likely the most promising, large uncertainties with the present statistics
      * NB: pT(V) and m(VH) very correlated in 0-jet selection


  * Isolation for photons and leptons
     * Some measurements include an isolation requirement for the photons or leptons into the definition of the fiducial region as the isolation efficiency depends on the production mode.
     * Provide corrections from isolated to full phase space in publications, preferably by production mode.

  * Normalized or non-normalized measurements?
    * Potential advantage: reduction of some experimental uncertainties, which will become more relevant when we are no longer dominated by statistical uncertainties.
    * As theoretical predictions are for cross sections, non-normalized cross sections are preferred in general. They also contain more information.
    * If the full experimental covariance matrix is provided, the normalization can be done easily. 


  * Information that is useful to include in publications to allow making maximal use of the results
    * cross correlations between different spectra. In addition, it would also be useful to provide the correlation between the differential distributions and the measured total (fiducial) cross section.
    * estimated nonperturbative effects
    * estimated contributions of non-ggH modes
    * acceptance corrections to allow extrapolation from fiducial region to full phase space (for convenience)

  * Background subtraction?
    * Experimentally H->gammma gamma makes more sense fully background subtracted
    * H->ZZ->4l or H->WW->2l2nu could give measurements including irreducible background (with appropriate fiducial phase space definition including eg suitable m4l window in that case)
    * In that case prediction for irreducible background should also be provided to allow theorists to easily subtract it if desired



== Session 2 discussion ==

jet selection anti-kT R=0.4, pt>25-30 GeV, |eta|<4.5

== ggF ==

(|eta|<2.5)

0j : sigma times BR
 
1j : pT 100,200,(300,400)_mt,overflow

2j : bin in 2j exclusive and 3j inclusive, distributions mjj, Delta eta_jj, Delta Phi_jj

== VBF ==

2j : mjj, Delta eta_jj, Delta Phi_jj

== VH ==

fully leptonic: mVH 300...500, overflow

1l, 0l: mT>200 GeV


== ttH ==

m_T(ttH) ...,500,...
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