Single top quark production in flavor-changingZ′models

Abstract

In some models with an extra U (1) gauge boson Z ′ , the gauge couplings of the Z ′ to different generations of fermions may not be universal. Flavor mixing in general can be induced at the tree level in the up-type and/or down-type quark sector after diagonalizing their mass matrices. In this work, we concentrate on the flavor mixing in the up-type quark sector. We deduce a constraint from D 0 − D 0 mixing. We study in detail single top-quark production via flavor-changing Z ′ exchange at the LHC and the ILC. We found that for a typical value of M Z ′ = 1 TeV, the production cross section at the LHC can be of the order of 1 fb. However, the background from the Standard Model single top-quark production makes it difficult to detect the flavor-changing Z ′ signal unless with a decent charm tagging method. On the other hand, at the ILC, the production cross section at the resonance energy of √ s ≈ M Z ′ can reach a size of more than 100 fb. Even away from the resonance, the cross section at ILC is shown to be larger than the threshold of observability of 0.01 fb.

Top quark forward–backward asymmetry

“…[5] can be derived in a certain class of non-universal Z ′ models [10]. The extra Z boson couples to fermions in interaction basis with …”

Enhancing thj production from top-Higgs FCNC couplings

“…mechanism [15][16][17][18]. But they can be greatly enhanced by the extended flavor structures in many new physics models, for example the minimal supersymmetric model (MSSM) with/without R-parity [19][20][21][22][23][24][25][26][27][28][29][30][31][32], two-Higgsdoublet model (2HDM) type-III [33][34][35][36][37][38][39][40][41][42][43][44][45], and the other miscellaneous models [46][47][48][49][50][51][52][53][54][55][56][57][58][59][60]. So the study of top-Higgs FCNC interactions is a common interest of the theory and experiment communities [61][62][6...…”

Flavor changingZ′couplings at the LHC

“…This process has a smaller crosssection than the one discussed in Ref. [6], but it also has significantly lower background. It can also be described in a more model independent way as we will show.…”

“…This feature makes the predictions very model dependent, a problem that has been addressed in Ref. [6] by surveying a large range of models. Second, it appears that the signal will be very difficult to separate from background at the LHC.…”

“…A possibility that has been discussed in Ref. [6], is the production of tc and ct final states from on-shell Z ′ production using the largest tcZ ′ coupling allowed by D −D mixing. This procedure suffers from two drawbacks.…”