Discussion on Differential Higgs Cross Section Measurements

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• 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

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

(|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

2j : mjj, Delta eta_jj, Delta Phi_jj

fully leptonic: mVH 300…500, overflow

1l, 0l: mT>200 GeV

m_T(ttH) …,500,…