LHC Higgs XS WG2: EFT kickoff meeting

42/3-002 (CERN)



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Adam Falkowski (Universite de Paris-Sud 11 (FR)) , André David (CERN) , Gino Isidori (Istituto Nazionale Fisica Nucleare (IT)) , Michael Duehrssen-Debling (CERN)
Timetable is tentative, starting times may shift depending on discussion length

Summary of last meeting:

- Clear need for kappa_short-distance in pTH and mVV.

- Still discussing other points.


Adam Goals:


* Clarification after Mike’s question: focus on EFT based on SM fields, in particular linear realization of electroweak symmetry breaking (Higgs part of SU(2) doublet); motivated by the closeness of data to SM predictions



* Form-factor in step 3: EFT inspired way to express the q^2 dependence of the Lorentz structure of a process with minimal set of model-independent pseudo-observables

- differential observables can be defined without recourse to the wilson coefficients

* step 3: potentially more parameters in step 3 than 4 and 5, because all processes are independent in step 3 without correlations. Advantage of step 3: identify all potential observables

* Mike: non-trivial reasons to consider non-linear realizations. Form-factor works also for non-linear realizations

* Goal: build correlation between observable, which are EFT inspired but don't depend on a basis choice

- step 3, Gino “the B-physics form factor slope is in the PDG and completely general”

- Mike: 2499 are mostly 4-point fermion flavour operators (at LEP it was 140 lepton sector parameters that one started from)

- Michael: h->Zff can be rotated to ff->Zh

- Andre: production can be factorized away if we are on-shell => m4l = 125

- Andre: Step 4 works if cut around on-shell Z is narrow (around +-10 GeV)

* kinematical dependence in H->Zll and H->Zgam given by known expressions. Coefficient c in Zgam independent of cuts with CP conservation. In reality uncertainty on c because experimental selection on Z is not narrow. Narrow ~ +-10GeV. For the moment gam*gam* and gamgam* explicitly avoided by the narrow Z cut. Exercise: try to quantify gamgam* and gam*gam* pollution.

- Andre: In chiral pert theo there are cases where the observables are correlated like in step 4

- Michael: Instead of pushing VH, can it be related to VBF with more parameters because both V off-shell. Extension to VBF possible, but additional parameters in VBF. For VBF same danger of going out of validity as in EFT. Pure form-factor good start for VBF

- Andre/Adam: for observables where dimension-6 operators do not contribute (by accident or by symmetry), dimension-8  operators  may be relevant; also the tails where large q2 can give rise to dim8;



- basically proposing the framework for simultaneous fits, not this particular lagrangian/parameterisation

* question on background model: first slides are signal only: optimal case

* A5 operator absorbed into A1 operator for on-shell Higgs

* Mike: question about consistent counting of what is kept in the lagrangian and what is removed. Is the starting Lagrangian non-redundant? Contact-interactions neglected? Guess that the fermionic contact interactions can be included in the box. If EW precision observables are included, the shown operators should be the relevant ones.

* ZZ has sensitivity to gamgam couplings



* Mike questions whether all LEP measurements are 0.1-1% precision. Says some/many LEP(2) are only ~10%

Mike: simplifications and external constraints: LEP measurements come with the assumptions made there (like the flavor symmetry that bring the #parameters down from 140)

Gino: flavor is a symmetry assumption that can be tested: h->mutau, h->4e vs h->4mu, etc.

- symmetries: flavor (program of tests can be devised), custodial (needs program of tests), CP (program of tests already under way)

* when discussion parameter reduction, assign control measurements to each assumption made (for example, when custodial symmetry assumed devise tests of this assumption in terms of h>WW and h>ZZ observables)


There are minutes attached to this event. Show them.
    • 09:30 10:00
      • 09:30
        Summary and conclusions of previous meeting on kappa formalism 15m
        Speaker: Michael, Gino, André, Adam
      • 09:45
        EFT goals for WG2 15m
        Speaker: Adam, André, Gino, Michael
    • 10:00 11:00
      h->4l in EFT
      • 10:00
        From kappa formalism to EFT (the h->4l case) 20m
        Speaker: Gino Isidori (Istituto Nazionale Fisica Nucleare (IT))
      • 10:30
        h->4l: simultaneous constraints on all EFT coefficients 20m
        Speaker: Roberto Vega-Morales (LPT-Orsay)
    • 11:00 11:30
      Simplified EFT
      • 11:00
        Simplified EFT: example of vector boson pair production 20m
        Speaker: Adam Falkowski (Universite de Paris-Sud 11 (FR))