Cascade decays of heavy Higgs bosons through vectorlike quarks in two Higgs doublet models

Abstract

We study cascade decays of heavy neutral Higgs bosons through vectorlike quarks. We focus on scenarios where decay modes into pairs of vectorlike quarks are not kinematically open which extends the sensitivity of the LHC to larger masses. Assuming only mixing with the third family of standard model quarks the new decay modes of heavy Higgs bosons are: H → t 4 t → W bt, Ztt, htt and H → b 4 b → W tb, Zbb, hbb, where t 4 (b 4 ) is the new up-type (down-type) quark mass eigenstate. We identify the region of the parameter space where these decay modes are significant or can even dominate. We also find that the rates for these processes can be much larger than the rates for a single production of vectorlike quarks. Thus, in the identified regions, they provide the best opportunities for the discovery of a new Higgs boson and vectorlike quarks. In the numerical analysis we assume the CP even Higgs boson in the two Higgs doublet model type-II but the signatures are relevant for many other scenarios.Among the simplest extensions of the standard model (SM) are models with extra Higgs bosons or vectorlike matter. Many searches for such individual new particles have been performed. However, if both sectors are present, new search strategies can be designed that could lead to a simultaneous discovery of heavy Higgs bosons and matter particles. These can be even more potent than separate searches. In this paper we focus on cascade decays of a heavy neutral Higgs boson through vectorlike quarks.We consider an extension of the two Higgs doublet model type-II by vectorlike pairs of new quarks (VLQ), corresponding to a copy of the SM SU(2) doublet and singlet quarks and their vectorlike partners, introduced in ref. [1]. Assuming only the mixing with the third family of standard model quarks, the flavor changing couplings of W , Z and Higgs bosons between new quarks and the third family quarks are generated. These couplings allow new decay modes of the heavy CP even (or CP odd) Higgs boson: H → t 4 t and H → b 4 b, where t 4 and b 4 are the lightest new up-type and down-type quark mass eigenstates. Although these decay modes compete with H → tt and H → bb we will see that, in a region of the parameter space, they are significant or can even dominate. Here we assume that the light Higgs boson (h) is SM-like so that H → ZZ, W W are not present. Subsequent decay modes of t 4 and b 4 : t 4 → W b, t 4 → Zt, t 4 → ht and b 4 → W t, b 4 → Zb, b 4 → hb lead to the following 6 decay chains of the heavy Higgs boson: H → t 4 t → W bt, Ztt, htt, (1.1) H → b 4 b → W tb, Zbb, hbb, (1.2)which are also depicted in figure 1.

Signals with six bottom quarks for charged and neutral Higgs bosons

“…Complementary signatures of cascade decays of heavy neutral Higgs bosons through vectorlike and SM quarks, relevant when vectorlike quarks are lighter than the new Higgs bosons, were recently studied in ref. [9]. Besides the opposite required hierarchy in masses, the main difference from the decay modes discussed here is that the flavor violating decays H → t 4 t and b 4 b, resulting from Yukawa couplings that mix vectorlike and SM quarks, have to compete with the usual decay modes of heavy Higgs bosons, H →tt andbb.…”

“…For example, we do not show and will not consider cases such as t 4 → Ht → tbb or b 4 → Hb → ttb. In these decay chains, the branching ratios of vectorlike quarks and those of the neutral Higgs boson are large in different regions of tan β [8,9] and the combined branching ratio for the whole chain is not large for any tan β. Thus these topologies are suppressed compared to the ones shown.…”

Tau-jet signatures of vectorlike quark decays to heavy charged and neutral Higgs bosons

“…Related signatures of cascade decays of heavy neutral Higgs bosons through vectorlike and SM quarks were recently studied in ref. [16]. These decay modes, depending on the size and the structure of Yukawa couplings of vectorlike quarks, are relevant when vectorlike quarks are lighter than the new Higgs bosons.…”

“…Details of the model have been presented in refs. [1,16]. The pair production cross section of new quarks depends only on their mass, see figure 2, while the typical BRs of both new quarks and heavy Higgs bosons depend only on tan β.…”

“…figure 3 of ref. [16]). Moreover, branching ratios of both heavy neutral and charged Higgses into quarks and leptons are strongly correlated.…”