Global fits of Higgs properties and new physics

• Applicants: Professor Herbert Dreiner, Ph.D.; Professor Dr. Michael Krämer, since 10/2017
• Subject Area: Nuclear and Elementary Particle Physics, Quantum Mechanics, Relativity, Fields
• Term: from 2015 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 257416295

A main objective of the LHC is the search for and the possible discovery of new physics beyond the Standard Model. An essential aspect is the quantitative interpretation, i.e. fits, of the data in terms of existing, well-motivated new physics models. These can be complete models, such as the constrained minimal supersymmetric model (CMSSM), effective TeVscale models like the general MSSM, or ¿simplified models¿, constructed to understand a subset of the data in terms of easily understandable physical parameters. At all times, these new models are competing against the Standard Model with the decisive measure being the quality of the fit. A technically and physically related problem is the study of the Higgs sector, either in a targeted Higgs fit or in combination with other signatures for BSM physics.The LHC results already place severe restrictions on BSM physics. In supersymmetry the key measurements are the Higgs mass, numerous direct search limits for strongly interacting particles like the gluinos and squarks, and more recently also only weakly interacting particles like the winos and neutralinos. The Higgs couplings can be included in a global analysis but do not yet have decisive impact. Furthermore, there are indirect constraints, where the supersymmetric particles enter through quantum corrections, for example in rare meson decays, as well as the dark matter relic density and direct and indirect dark matter detection limits. The latter are only relevant for R-parity conserving supersymmetry.The inclusion of limits on the production cross sections of new particles is technically and conceptually difficult. Furthermore, for example, in the CMSSM, a complete model with only five new free parameters beyond the Standard Model, there are expected strong correlations between observables, such as between the anomalous magnetic moment of the muon (g - 2)µ and the B-meson branching ratio BR(Bs- µµ) [1]. In more extended models with a larger set of parameters, the impact of such correlations is typically weakened. A central focus of current LHC parameter fits is the study of such model-dependent correlations between the different new physics sectors. In addition, it is also important to develop measures for the quality of fit, even for larger parameter models, for example through toy models.

• DFG Programme: Research Units
• Subproject of: FOR 2239: New Physics at the Large Hadron Collider
• Co-Investigators: Professor Dr. Joachim Kopp; Professor Dr. Tilman Plehn
• Ehemaliger Antragsteller: Professor Dr. Jamie Tattersall, until 9/2017