Light Mass Higgs meeting 1

40/2-A01 (CERN)



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1. Mass

a) As long as the width is much smaller than the resolution, effects on value determination are negligible (this is the case for the SM Higgs with mH<2*mW).

b) Any uncertainties from the Higgs lineshape would be of order width/mass

c) Experiments can use whatever method they want to extract the mass, as long as it is shown to satisfy closure tests against the MC.
==> ## TH contacts: assess impact of going from mass used in MC(s) (see above) to the real part of the complex propagator.
==> ## EXP: is it possible to use functional forms instead of templates from MCs?

d) Theory experts expressed the wish that experimentalists state clearly which generator and which Higgs line shape model was used for Higgs production/decay, such that a later conversion into a different model is possible
==> ## EXP contacts: make table of generators being used for Higgs signal samples and contact authors for the needed details

e) Setting a limit to line shape width is a PDG-grade measurement that is unlikely to exclude any BSM model, but nevertheless valuable. It was stated that all nowadays conceivable BSM models have a width <<1GeV for mH~125GeV

2. Couplings

A lot of aspects were discussed, but no "final" solutions were found. The discussed topics were

a) How model-independent can a measurement be?
Focused on the aspect of interference terms (e.g. H->WW and H->ZZ) decays that make it problematic to assign a uniform Higgs coupling to these processes
==> one possibility: look at final states, e.g. 4l instead of ZZ
==> also a question of precision. Many of these effects are small and probably not relevant for ~30-50% measurements

b) model-independence vs. accuracy of measurement
Can start from two directions: a "completely" model independent measurement that is increasingly restricted with theory assumptions. Or a SM "measurement" that is increasingly generalized by removing assumptions that the SM Higgs fulfills
==> no clear recommendation was made, advantages/disadvantages need to be discussed further

c) large number of scenarios vs. manpower
(Experimental) manpower is limited and number of models is infinite. Expressed the general wish of models with well chosen pseudo-observables that match large classes of models
==> need to discuss pseudo-observables further. Several well chosen sets of these could solve many of the issues discussed in a) and b)
==> need also decide how good the pseudo-observables (concerning their precision) need to be for this year and for the future.

3. Self-coupling
very difficult measurement, but some statement is wanted/needed for the European strategy document.
Revised studies on the upgraded LHC potential for triple- and quartic-coupling measurements could benefit from improved theoretical description, which might not be available on the timescale of the report for the European Strategy meeting.

4. Tensor structure
Discussion postponed to the next meeting.
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