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Combined EFT interpretation of top quark, Higgs boson, electroweak and QCD measurements at CMS
by Niels Van den Bossche
Submission summary
| Authors (as registered SciPost users): | Niels Van den Bossche |
| Submission information | |
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| Preprint Link: | https://arxiv.org/abs/2501.02957v1 (pdf) |
| Date submitted: | Jan. 8, 2025, 1:51 p.m. |
| Submitted by: | Niels Van den Bossche |
| Submitted to: | SciPost Physics Proceedings |
| Proceedings issue: | The 17th International Workshop on Top Quark Physics (TOP2024) |
| Ontological classification | |
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| Academic field: | Physics |
| Specialties: |
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| Approach: | Experimental |
Abstract
A recent EFT result from CMS is presented, combining differential cross section and direct EFT measurements performed by the CMS Collaboration across four branches of the Standard Model: top, Higgs, electroweak and QCD physics. To maximize the sensitivity, measurements of electroweak precision observables from LEP and SLC are included as well. 64 Wilson Coefficients (WC) are targeted in this combined measurement, both individually and with a simultaneous fit to 42 linear combinations of the Wilson Coefficients.
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Requested changes
1 Effective Field Theory (EFT) allows for the extension of the Standard Model (SM) Lagrangian with various new physics effects in a model-independent way. -> The EFT approach is definitely more general than a concrete BSM scenario, but there are several assumptions (new physics kicks in at a scale beyond that directly reached by the experiments, respects the SM gauge structure, and can be approximated with the c/Lambda^2 series truncated after the first term). Please, add a statement to this effect and qualify the statement that EFT is model-independent.
2 This result targets the tightest constraints on the SMEFT operators. -> I think that is a fair summary. Often, tight constraints are preferred over more generally valid bounds. The validity and uncertainties of the SMEFT are an open issue that the broader community has failed to find a uniform solution to. The author presents bounds of linear fit (including only interference terms of the SM with dimension-6 operators) and a quadratic fit (including also dimension-6-squared terms), which is still the standing recommendation of the LHC top WG, for lack of a better solution. There is, however, no discussion of the results. The large difference between bounds from the two fits for some operators signals that the validity of the SMEFT expansion is marginal and special care should be taken when reinterpreting these results. The paper claims "special care has been taken to ensure the applicability of the obtained confidence intervals, even if the contributions quadratic in the WC are considered." Please, point this out and warn the reader that the bounds on several operator coefficients cannot readily be re-interpreted in any BSM scenario.
3 One of the main advantages of performing this type of combination within the collaboration is the availability of the full likelihoods of these results -> The likelihoods could easily be shared with the broader HEP community, enabling ATLAS+CMS joint fits and facilitating the inclusion of the results in fits by theory groups. Correlations across the measurements are, however, not always available, even within the experiments. Please, expand this discussion.
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