Higgs coupling to the heavy quark sector and lattice QCD – LatHiggs

The starting of Large Hadron Collider (LHC) in 2008 has been a key moment for high energy physics. Even if the Standard Model of particle physics (SM) revealed very robust versus numerous experimental tests performed since 40 years, some questions are still open and the SM has to be seen as an effective theory of low energy. It is particularly the case in flavor physics: origin of the strong hierarchy observed among quark masses, dynamics at work in the mixing pattern among quark flavors, excess of baryon-antibaryon asymmetry observed in Universe with respect to sources of CP violation contained in SM. Thus one has in mind to test the full set of New Physics models (NP), whose goal is to describe interactions at higher energy than the electroweak scale, versus experimental measurements that are available at the moment or in the next future. To fully exploit experimental data in flavor physics, detect deviations from the SM and then constrain efficiently NP scenarios, theorists have to reduce as much as possible uncertainties coming from the confinement of quarks in hadrons, in particular by means of lattice QCD simulations. Under that general respect the ambition of “LatHiggs” is to provide hadronic inputs to study how the Higgs sector is coupled to the heavy quark sector and to shed light on the dynamics at work in the string splitting of heavy hadrons.
The Higgs field interacts with charged leptons and quarks through Yukawa couplings. A non-zero vacuum expectation value of the Higgs field induces a Dirac mass term for those fermions. Scenarios of NP are proposed with different extensions of the Higgs sector that can be discriminated by experiment, but only after a sufficiently good control on the hadronic side of the processes. Testing the existence of a light CP-odd Higgs boson, tracked by its mixing with quarkonia states, brings useful information if one knows the hadronic parameters associated to the leptonic width of pseudoscalar quarkonia. Our project aims to greatly improve the systematic error attached to those parameters. Scenarios beyond the SM allowing weak decays mediated by a charged Higgs through a right-handed current receive a lot of attention in the framework of 2 Higgs doublet models: semileptonic decays of Bc meson into charmonia that are investigated at LHCb need a theoretical effort to determine the form factors encoding the long-distance effects of QCD, purpose of our project as well. After dedicated studies to make systematically clean the extraction of physical information from correlation functions, obtained after a lattice simulation, and to cure large cut-off effects induced by simulating heavy quarks on the lattice, our program will study the impact that our results have for bounds on couplings of the extended Higgs sector to the heavy quark sector.
Main properties of the strong interaction, confinement and spontaneous breaking of chiral symmetry, offer a particularly rich dynamics: understanding multihadronic states is a challenge both for theorists and experimentalists. Phenomenological models, that are helpful to fulfil it, need lattice QCD to be validated in regions of the phase space where the latter method is tractable: the project we are presenting plans to examine an illuminating example, the strong decay of excited charmonia. The “3P0 creation pair” quark model was found to describe qualitatively well a wide class of vector meson decays into a pair of pseudoscalar mesons, once a universal coupling is fixed: numerical simulations can help to reveal the mechanism responsible for that phenomenological observation.