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===== Using Higgs fiducial cross sections and differential distributions to constrain new physics =====

Interested people: Kentarou, Sabine, Benj, Stefania, Stefan, Jérémie, Ursula, Kristin, Fabio, Andy **add your name if interested**

The use of signal strength measurements (kappa framework, reduced couplings...) for constraining deviations from the SM is well established, and public tools (HiggsSignals, Lilith) exist for performing fits to the data. Two limitations of the signal strength approach are that it assumes 
  - the SM tensor structure
  - that there are no new Higgs production modes (e.g. from decays of heavier states)

If new operators and/or new Higgs production modes are present, this can change the kinematic distributions and thus the signal acceptance. This can be tested with fiducial cross sections, [[https://phystev.cnrs.fr/wiki/2017:groups:higgs:stxs | STXS]], differential distributions. However, appropriate tools and explicit studies using the available measurements are still missing. 

Rivet routines are available for the ATLAS diphoton and 4l measurements at 8 TeV. These could be used to constrain additional Higgs production from e.g.
  * A -> Zh
  * VLQ decays to Higgs
  * Higgs production from SUSY cascades, e.g. pp -> sbottom pair -> bbH(H) + MET, see https://arxiv.org/abs/1703.06544, or pp -> chi_1 chi_2 -> H + MET 
  * single hZ, hW, h+MET
  * X -> h+l, h+gamma, h+jet, h+b, h+t

ATLAS 8 TeV Rivet routines are easily converted to CMS8TeV and/or 13 TeV measurements; plots however need to be digitalised, not all is on hepdata.

One interesting point would be to identify what can be done with and without this. Checking how constraints vary.

See also this [[https://indico.cern.ch/event/525142/contributions/2173709/attachments/1292787/1926290/Talk_PDF.pdf|talk by F. Bernlocher]] on HFXS at Reinterpretation Forum meeting June 2016.

=== ATLAS and CMS results ===

| ^ gamma-gamma ^ ZZ*->4l ^ WW*->2l2nu ^
^ 8 TeV | [[https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HIGG-2013-10/|ATLAS-HIGG-2013-10]]  | [[https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HIGG-2013-22/|ATLAS-HIGG-2013-22]] | [[https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HIGG-2015-04/|HIGG-2015-04]] |
| | [[http://cms-results.web.cern.ch/cms-results/public-results/publications/HIG-14-016/index.html|CMS-HIG-14-016]] | [[http://cms-results.web.cern.ch/cms-results/public-results/publications/CMS-HIG-14-028/index.html|CMS-HIG-14-028]] | [[http://cms-results.web.cern.ch/cms-results/public-results/publications/CMS-HIG-15-010/index.html|CMS-HIG-15-010]] | 
^ 13 TeV | [[https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/CONFNOTES/ATLAS-CONF-2016-067/|ATLAS-CONF-2016-067]] | [[https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/CONFNOTES/ATLAS-CONF-2017-032|ATLAS-CONF-2017-032]] |  | 
| | [[http://cms-results.web.cern.ch/cms-results/public-results/preliminary-results/HIG-17-015/index.html|CMS-HIG-17-015]] | | 


=== Concrete project proposals ===

  - 'Generic' study 
    - Simulate signal for above mentioned scenarios, let Higgs decay to 2 photons or ZZ*, run through Rivet analysis (or your own implementation of the fiducial cuts) and put result on top of SM expectation for fiducial Xsection and differential distributions published by the collaboration.
    - For the cases with a visible effect, compute the chi^2. Beware, the various histograms are not statistically independent, one needs to determine the most sensitive bin from all histograms. In principle [[https://contur.hepforge.org|Contur]] does exactly this, but it assumes SM=data, so this needs to be extended by the actual SM prediction.  
    - Wouldn't it be instructive to quantitatively estimate the gain from a pure signal strength approach? 
  - 2HDM-spcific study: From a general scan of the 2HDM fitting all the Higgs constraints in the usual way (signal strengths, cross section limits on heavy Higgs production), take the points with largest cross sections for pp->A->Zh and see whether these would contribute in any significant way to the fiducial Higgs measurements. Best consider 2HDM Type I, as it allows for lighter A. The plots below show the cross sections for gg->A->Zh at 13 TeV in the quasi-alignment limit from [[https://arxiv.org/abs/1507.00933|1507.00933]]:

{{:2017:groups:higgs:ma_gga13_zh_tb_cv99_h_i_l2h.jpeg?direct&200|}}{{:2017:groups:higgs:ma_gga13_zh_tb_cv99_h_ii_l2h.jpeg?direct&200|}}


=== Ongoing or planned activities ===

  * Benjamin and Fabio want to produce [[2017:groups:higgs:fxsnp:ufo|UFO file]] for 'weird Higgs production' modes
  * Ursula is looking at Higgs production from sbottom decays, see [[2017:groups:higgs:fxsnp:susycascades|first results here]].


=== Some more references ===

  * Higgs Strahlung at the Large Hadron Collider in the 2-Higgs-Doublet Model. Robert V. Harlander, Stefan Liebler, Tom Zirke. http://arxiv.org/abs/arXiv:1307.8122
  * Gluon-initiated associated production boosts Higgs physics. Christoph Englert, Matthew McCullough, Michael Spannowsky. http://arxiv.org/abs/arXiv:1310.4828
  * Higgs characterisation via vector-boson fusion and associated production: NLO and pardon-shower effects. Fabio Maltoni, Kentarou Mawatari, Marco Zaro. http://arxiv.org/abs/arXiv:1311.1829  (plus the other Higgs characterisation papers)
  * The compatibility of LHC Run 1 data with a heavy scalar of mass around 270 GeV. Stefan von Buddenbrock et al. http://arxiv.org/abs/arXiv:1506.00612
  * //add more ...//

=== Blackboard of the discussion ===
{{:2017:groups:higgs:img_0586.jpg?400|}}
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