WG2: Discussion of pseudo-observables for Higgs measurements

222/R-003 (CERN)



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Adam Falkowski (LPT Orsay) , André David (CERN) , Frank Tackmann , Gino Isidori (Universitaet Zuerich (CH)) , Kerstin Tackmann (Deutsches Elektronen-Synchrotron Hamburg and Zeuthen (DE)) , Michael Duehrssen-Debling (CERN) , Sabine Kraml (Centre National de la Recherche Scientifique (FR))


Simplified cross sections:

Frank reported on the discussions in Les Houches and summarized the main idea behind this ansatz of “model independent” measurements of Higgs productions. Topics of discussion:

  • What to do if analyses are not sensitive to certain splits of the parameters. E.g. H->gamgam is likely not strongly separating ggH 0j and ggH 1j
    ⇒ Experiments should then report the sum of parameters they measure, so for the example above sigma(ggH0j)+sigma(ggH1j) and not try to separate these two components. In general, any linear combination of POs could be given as result of a measurement, if this resembles to what the measurement is truly sensitive

  • Split of VH seen as too fine grained
    ⇒ Likely true, so experiments will not be able to report all components initially. As above, they should report the sum of the components that is measured

  • Some discussion of parameters in VBF and how well the current choice matches possible deviations from the SM
    ⇒ BSM regions still need to be defined, proposals/studies very welcome!
    ⇒ Would be good to have some EFT studies to check how well/badly the current categories cover BSM deviations
    ⇒ Continuous POs as defined for H->VV decays could be a (better) alternative in some cases, e.g. CP-odd BSM contributions. Most parameters for H->VV also valid for VBF and VH. Only for the contact terms (HVff and Hffff coupling) the Q^2 expansion used in H->VV is likely not sufficient

  • Studies on continuous POs for VBF and/or VH so far missing but highly wanted


Update on PO for Higgs decays:

Gino reported on updates for POs in Higgs decays. He showed that soft QED radiation effects factorize and can be taken into account. The 20 POs for H->VV, H->Zgam, H->gamgam can be defined as components of partial width.

  • Some discussion on how uniquely the components of the partial width are defined
    ⇒ Especially for the CPV components the definition as in the slides might not be the best. An asymmetry could be better. Participants are invited to make a better/more suitable proposal for the CPV components

  • Question if the soft QED radiation effects could be taken into account on the experimental side with Photos or similar
    ⇒ yes, this is similar/identical to what was done for the distributions shown in the talk. However, NLO EW normalization (as Prophecy4f gives it in the SM) is obtained “by hand”, but corresponds to a redefinition of the kappa and epsilon parameters.


Tools for PO:

Admir reported on the development of the HiggsPO tool based on FeynRules and Madgraph in order to simulate H->VV, H->Zgam, H->gamgam

  • Question if this implementation could also be used for Higgs production.
    ⇒ yes, for LO simulation of Higgs production (VBF, VH). However, for now the HZff contact terms are not implemented for quarks, but this is a trivial extension
    ⇒ no, for NLO QCD simulation

  • Question if this implementation works together with MadSpin, which would allow a seamless integration with Powheg for gg->H production


Preparation of a pseudo-observable writeup:

Michael discussed the plans for the joint PO writeup for YR4 and LesHouches. People interested in joining/helping should contact the WG2 conveners. The work will proceed in a similar way as for the EFT basis note. A first draft will be prepared by all people agree to help. This draft is then circulated to WG2 for feedback. Depending on feedback, several rounds of iterations might be needed.


There are minutes attached to this event. Show them.
    • 10:00 AM 10:30 AM
      Simplified Cross Section Framework 30m
      Speaker: Frank Tackmann (Deutsches Elektronen-Synchrotron (DE))
      Les Houches summary
    • 11:00 AM 11:15 AM
      Update on PO for Higgs decays 15m
      Speaker: Gino Isidori (Universitaet Zuerich (CH))
    • 11:20 AM 11:35 AM
      Tools for PO 15m
      Speaker: Admir Greljo (University of Zurich)
    • 12:00 PM 12:30 PM
      Preparation of a pseudo-observable writeup 30m