LHC EFT WG meeting

Monday 8 Jul 2024, 17:00 → 18:30 Europe/Zurich

Nicholas Wardle (Imperial College (GB))

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Recording

1 EFT at Jade: A Case Study (20'+10')

As we use the standard model effective field theory to search for signs of new physics beyond the reach of the LHC, we often wonder what we may learn from the EFT, and what it would look like to make a discovery via EFT.

This talk presents a case study that provides some answers to these questions.
We apply the low-energy effective field theory to $e^+e^- \to \mu^+\mu^-$ data below the $Z$ boson mass, from the JADE experiment at DESY.

The low-energy effective field theory allows the observation of physics beyond QED in the JADE data, and furthermore, by matching the Wilson coefficients to the electroweak theory, a rough measurement of the masses of the $W$ and $Z$ bosons is possible.
This rough measurement would have been sufficient to guide the construction of colliders such as $Sp\bar{p}S$ or the large electron-positron collider, and so we anticipate that a discovery of new physics via effective field theory at the LHC would be similarly sufficient to guide the construction of future colliders.

Speaker: Jon Wilson (Baylor University (US))

arXiv:2407.03468

JADE_EFT_case_study_LHC_EFT_WG_July_8.pdf

2 A critical study of the Monte Carlo Replica method (20'+10')

We present a detailed mathematical study of the Monte Carlo replica method as applied in the global fitting literature from the high-energy physics theory community.

For the first time, we provide a rigorous derivation of the parameter distributions implied by the method, and show that, whilst they agree with Bayesian posteriors for linear models, they disagree otherwise. We proceed to numerically quantify the disagreement between the Monte Carlo replica method and the Bayesian method in the context of two phenomenologically relevant scenarios: fits of the SMEFT Wilson coefficients, and fits of PDFs (albeit in a toy scenario). In both scenarios, we find that uncertainty estimates of the quantities of interest are discrepant between the two approaches when non-linearity is relevant. Our findings motivate future investigation of Bayesian methodologies for global PDF fits, especially in the context of simultaneous determination of PDFs and SMEFT Wilson coefficients.

Speaker: Mark Costantini

arxiv:2404.10056

costantini_mc_sampling.pdf

3 Exploring the Flavor Symmetry Landscape (20'+10')

We explore flavor dynamics in the broad scenario of a strongly interacting light Higgs (SILH). Our study focuses on the mechanism of partial fermion compositeness, but is otherwise as systematic as possible. Concretely, we classify the options for the underlying flavor (and CP) symmetries, which are necessary in order to bring this scenario safely within the range of present or future explorations. Our main goal in this context is to provide a practical map between the space of hypotheses (the models) and the experimental ground that will be explored in the medium and long term, in both indirect and direct searches, in practice at HL-LHC and Belle II, in EDM searches and eventually at FCC-hh. Our study encompasses scenarios with the maximal possible flavor symmetry, corresponding to minimal flavor violation (MFV), scenarios with no symmetry, corresponding to the so-called flavor anarchy, and various intermediate cases that complete the picture. One main result is that the scenarios that allow for the lowest new physics scale have intermediate flavor symmetry rather than the maximal symmetry of MFV models. Such optimal models are rather resilient to indirect exploration via flavor and CP violating observables, and can only be satisfactorily explored at a future high-energy collider. On the other hand, the next two decades of indirect exploration will significantly stress the parameter space of a large swath of less optimal but more generic models up to mass scales competing with those of the FCC-hh.

Speaker: Alfredo Glioti (IPhT)

arxiv:2402.09503

Glioti - Flavor.pdf