Research Area Higgs

Higgs precision physics

One theme of research is to challenge the Standard Model of particle physics with Higgs precision measurements and to explore the Higgs sector as a window to new physics in close collaboration between experiment and theory. The emphasis has been on differential measurements in various Higgs decays, allowing the study of kinematic properties and specific regions of phase space. A measurement of the Higgs boson mass with a precision of 0.17% has been obtained in H → ZZ∗ → 4l decays. Differential and simplified template cross sections have been developed and measured. Higgs predictions for spectrum and cross section have been performed at three loops and predictions for Higgs mass and uncertainties obtained in different scenarios of the Minimal Supersymmetric Standard Model (MSSM).

Another important set of studies has been of Higgs Yukawa couplings and CP properties using data taken during Run 2 and 3 at LHC, and on related theoretical advances. Yukawa couplings to the top quark, b-coupling, and second generation fermions are of interest. Couplings in minimal flavour violation have been explored. Potential CP-violation in Yukawa interactions have been investigated as well as constrained from inclusive and differential results from ATLAS and Compact Muon Solenoid (CMS) experiments at LHC. Furthermore, several new results regarding global interpretations, the Higgs potential and self-interactions, as well as the stability of the vacuum have been obtained. 

Additional Higgs bosons and cosmological implications

Another focus of research investigates additional Higgs bosons and their cosmological implications. The goal is to directly discover, at the LHC and/or at future colliders, siblings of the Higgs boson or reveal new, possibly dark, sectors which the Higgs would be coupled to. Explicit UV models, light degrees of freedom, and decays into light pseudo-scalars, top quarks or gauge bosons pairs have been analysed. The cosmological implications of the Higgs sector are also calculated, from its potential role in inflation to its mediator role between the SM and the dark matter as well as a potential source of a gravitational wave stochastic background. Also studied are electroweak symmetry restoration temperature, baryogenesis and axion fragmentation effects on relaxion mechanism to solve the hierarchy problem.

New algorithms and reconstruction techniques for boosted final states have been developed and implemented. New channels have been proposed to search for extended Higgs sectors, collider signatures of models where the Higgs is a portal to the dark sector have been investigated, the bounds obtained from the Higgs searches have been confronted with the predictions of a variety of models, and the dynamics of the electroweak transition (or the absence thereof) have been carefully studied in beyond the Standard Model (BSM) scenarios. 

Novel high precision detection techniques 

Detector concepts have been developed based on extreme spatial granularity combined with time resolution and the corresponding pattern recognition algorithms for future experiments. Our focus extends to pixel detectors with picosecond time resolution and the necessary development of advanced microelectronics. 

A modular detector system has been designed for a highly granular calorimeter in a high radiation environment and characterisation of radiation damage in SiPMs has been modelled. Position reconstruction for segmented silicon-based detectors before and after exposure to high-dose particle radiation has been investigated and an improved model developed to simulate and extract their resolution. First results using Cherenkov light to extract the particle direction have been obtained and the identification of showers along-side muon tracks in the Jiangmen Underground Neutrino Observatory (JUNO) serves to improve the veto strategies and statistics.

Detector advancement results with machine learning (ML) include voxel-wise reconstruction of energy deposit in pure liquid scintillator detector, software compensation for energy reconstruction of hadronic showers, shower separation in highly granular 5D hadronic calorimeters and augmented Monte Carlo-based simulation with generative ML models. Investigations of Low Gain Avalanche Detectors (LGAD) with 20-30 picosecond time resolution is being conducted for timing layer development for test beam telescopes. The boron removal mechanism of radiation damage in LGADs has also been characterised.