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Doctor M/F HIGGS COUPLING TO HEAVY QUARKS AS A PROBE OF NEW PHYSICS SCENARIOS

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Français - Anglais

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General information

Reference : UMR8627-SARMEM0-003
Workplace : ORSAY
Date of publication : Friday, September 27, 2019
Scientific Responsible name : Benoît BLOSSIER
Type of Contract : PhD Student contract / Thesis offer
Contract Period : 36 months
Start date of the thesis : 1 November 2019
Proportion of work : Full time
Remuneration : 2 135,00 € gross monthly

Description of the thesis topic

The starting of LHC in 2008 has been a key moment for high energy physics. Even if the Standard Model of particle physics (SM) revealed very robust against 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, in particular 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. Direct searches of New Physics (NP) scan the energy range from 100 GeV up to the TeV scale while
increasing the luminosity allows to study lower energy processes that are highly suppressed in the SM and, hence, are sensitive to quantum fluctuations with exchanges of NP massive virtual particles. 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.
The Higgs field interacts with charged leptons and quarks through Yukawa couplings. Interactions with the quark sector, in particular c and b quarks, receive more and more attention compared to the electroweak sector. The motivation of the thesis is to closely examine c- cbar, b-bbar, b-sbar, c-sbar and b-cbar bound states as they shed light on scenarios of NP with various extensions of the Higgs sector. Testing the existence of a light CP-odd Higgs boson, tracked by its mixing with quarkonia states, made of a c-cbar or a b-bbar pair, brings useful information if one knows the hadronic parameters associated to the leptonic width of pseudoscalar quarkonia: the SM contribution to those decays is highly suppressed because it is mediated by quantum loops. Scenarios beyond the SM allowing weak decays mediated by a charged Higgs boson through a right-handed current are attractive as well: very recent analyses of semileptonic decays of B_c meson into vector charmonium and B_s meson into D_s or D*_s, performed at LHCb, give a further anomaly about flavor lepton universality, after those observed in B-->K(*)l+l- and B-->D(*)l nu_l; however an issue is the relatively large uncertainty on form factors encoding the long-distance effects of QCD.
After dedicated studies to make systematically clean the extraction of physical information from correlation functions of quarkonia, B_s, D_s and B_c meson, obtained after lattice QCD simulations, and to cure large cut-off effects induced by simulating heavy quarks on the lattice and the extraction of form factors in a wide range of q^2, this thesis will study the impact that the results will have for bounds on couplings of the extended Higgs sector to the heavy quark sector.

Work Context

Laboratoire de Physique Théorique d'Orsay (Laboratory for Theoretical Physics). This laboratory is a joint research unit (UMR 8627) of CNRS and Univ. Paris-Sud, located on the campus of the Science Faculty of Orsay (Université Paris-Saclay). Its main themes of research deal with particle physics, cosmology, statistical physics and mathematical physics.LPT is a pluridisciplinary laboratory involved in the understanding of the behaviour of matter in its less known aspects :

- infinitely small scales (particle physics),

- infinitely complex systems (statistical physics),

- infinitely large structures (cosmology).

These activities are based on common ideas and computing tools, studied and developed in mathematical physics.

The models built by LPT scientists are improved through a permanent comparison between their predictions and the results obtained by experimental teams : particle accelerators and colliders, experiment in solid-state and condensed-matter physics, astronomical observations...

Constraints and risks

NA

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