Light non-degenerate composite partners at the LHC

Abstract

Abstract:We study the phenomenological implications of a large degree of compositeness for the light generation quarks in composite pseudo-Nambu-Goldstone-boson Higgs models. We focus in particular on phenomenologically viable scenarios where the right-handed uptype quarks have a sizable mixing with the strong dynamics. For concreteness we assume the latter to be characterized by an SO(5)/SO(4) symmetry with fermionic resonances in the SO(4) singlet and fourplet representations. Singlet partners dominantly decay to a Higgs boson and jets. Since no dedicated searches are currently looking for these final states, singlet partners can still be rather light. Conversely, some fourplet partner components dominantly decay to an electroweak gauge boson and a jet, a type of signature which has been analysed at the LHC. We have reinterpreted various ATLAS and CMS analyses in order to constrain the parameter space of this class of models. In the limit of first two generation degeneracy, as in minimal flavor violation or U(2)-symmetric flavor models, fourplet partners need to be relatively heavy, with masses above 1.8 TeV, or the level of compositeness needs to be rather small. The situation is significantly different in models which deviate from the first two generation degeneracy paradigm, as charm quark parton distribution functions are suppressed relative to the up quark ones. We find that JHEP02 (2014)055 the right-handed charm quark component can be mostly composite together with their partners being as light as 600 GeV, while the right-handed up quark needs either to be mostly elementary or to have partners as heavy as 2 TeV. Models where right-handed uptype quarks are fully composite fermions are also analysed and yield qualitatively similar conclusions. Finally, we consider the case where both the fourplet and the singlet states are present. We demonstrate that in this case the fourplet bounds could be significantly weaken due to a combination of smaller production rates and the opening of new channels including cascade processes.

On the interpretation of Top Partners searches

“…First careful assessments of the light partner collider phenomenology was performed in refs. [59][60][61] but a systematic interpretation strategy is missing and could be developed following our method. Finally, it could be worth refining our theoretical predictions of the single production rates which, as explained in section 3.1, are extracted from available NLO results under some approximation.…”

Interplay of vector-like top partner multiplets in a realistic mixing set-up

“…Initially, simplifying assumptions were considered (mixing only with the third generation of SM quark family or specific decay modes) [23][24][25][26][27][28][29][30][31][32][33]. However the most recent analyses, due to larger data samples, allow exploring more general situations with mixing of VL quarks with the first two generation of SM quarks [34][35][36][37][38]. There are some works analyzing the phenomenology of exotic quarks [39].…”

Enhanced Higgs boson coupling to charm pairs

“…The ATLAS Collaboration, in fact, recently presented new experimental techniques designed to tag charm jets at the LHC [6]. The possibility to apply charm tagging, beyond its plain interest from the SM perspective [7,8], also opens new possibilities to analyze various beyond the SM signals [9][10][11][12]. In particular we show in this paper how crucial charm tagging may be in order to exhume the associated Higgs production signal in the case of a suppressed h → bb branching ratio due to an enhanced Higgs-to-charm coupling relative to the SM.…”