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HIGGSEFT Report Summary

Project ID: 631962
Funded under: FP7-PEOPLE
Country: Germany

Periodic Report Summary 1 - HIGGSEFT (Higgs precision era at the LHC)

The project is concerned about understanding and characterizing the physical properties and its couplings to other elementary particles of the Higgs boson, the ultimate particle discovered in 2012 at the Large Hadron Collider (LHC) experiment at CERN (Geneva). The goal of the project is to develop an Effective Field Theory (EFT) framework to analyze in a model-independent way the experimental data collected at the LHC and to utilize them to discover or put constraints on new physics beyond the standard model. Following the initial objectives, the main results obtained during the first period of the project are the following:
1. The renormalization group flow controlling, as a function of the characteristic energy of a process, the relative size and mixing of a set of operators relevant for Higgs physics and Electroweak Precision Physics has been derived. This set of equations allows for a consistent global fit for both types of data collected at different colliders.
2. The production of the Higgs boson in association with a highly boosted jet was studied as a way to probe the top Yukawa coupling and to distinguish it from a contact interaction between the Higgs and the gluons, an ambiguity the plagues inclusive quantities like the total Higgs production cross-section.
3. A study of the production of the Higgs away from its mass-shell with a subsequent decay into from leptons was performed. This channel has been analyzed by the two main LHC collaborations and was used to constrain the Higgs boson width. However, this interpretation requires several assumptions that are specific to a very particular class of models. Alternatively, the data can be used to study the energy dependence of the Higgs couplings and to put stringent bound on contact interactions that exhibit a energy-growing behavior and are thus particularly relevant in the off-shell regime.
4. A tool that computes all the Higgs branching decay ratios in the presence of new interactions has been developed and made publicly available to the whole community.

The PI of the project acquired an indisputable expertise in the field, a status demonstrated by the fact that he is one of the three theory conveners of the LHC Higgs Cross Section working group gathering more than 600 physicists and providing recommendations to the experimentalists. He is also in charge of the report on Higgs physics for the Review of Particle Physics of the Particle Data Group, a unique reference in the community.

In addition, the PI and his group was involved in the preparation of various documents to establish/clarify/strengthen the physics case of various future collider projects: International Linear Collider, Future Circular Collider with electrons and positrons.

In January 2015, the PI moved from IFAE, Barcelona to DESY, Hamburg as a leading scientist to lead the theoretical particle group. His main activities are still directly concerned with the topic of this project. His career integration grant partly supports two PhD students from Barcelona who are spending a significant part of their time at Hamburg. It is also used to support common workshops organized jointly by IFAE and DESY.

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