Search for vectorlike T quark through tZ channel at eγ collider

Abstract

In the framework of a simplified model, we investigated the vectorlike top quark partner $T$ via the channel $T\ensuremath{\rightarrow}tZ$ at future high energy $e\ensuremath{\gamma}$ collider. Under the current constraints, we calculated the production cross sections in the cases of unpolarized and polarized beams at $\sqrt{s}=2$, 3 TeV and found that the polarized beams can improve the detectability significantly due to the larger production rates. Considering the characteristics of various kinematic distributions of final states, we gave a set of cuts to select signal events and suppress background events effectively. For the unpolarized case at $\sqrt{s}=2\text{ }\text{ }\mathrm{TeV}$, we found that the top partner $T$ could be excluded in the correlation region of the coupling parameter ${g}^{*}\ensuremath{\in}[0.28,0.5]$ and mass ${m}_{T}\ensuremath{\in}[1300\text{ }\text{ }\mathrm{GeV},1530\text{ }\text{ }\mathrm{GeV}]$ at $2\ensuremath{\sigma}$ level and the integrated luminosity $\mathcal{L}=3000\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$. For the polarized case at $\sqrt{s}=2\text{ }\text{ }\mathrm{TeV}$, we found that the excluded correlation regions can be expanded to ${g}^{*}\ensuremath{\in}[0.17,0.5]$ and ${m}_{T}\ensuremath{\in}[1300\text{ }\text{ }\mathrm{GeV},1720\text{ }\text{ }\mathrm{GeV}]$, and the future collider has the potential of observing this signal in the discovery region ${g}^{*}\ensuremath{\in}[0.28,0.5]$ and ${m}_{T}\ensuremath{\in}[1300\text{ }\text{ }\mathrm{GeV},1520\text{ }\text{ }\mathrm{GeV}]$ at $5\ensuremath{\sigma}$ level. For the polarized case at $\sqrt{s}=3\text{ }\text{ }\mathrm{TeV}$, we can see the correlated regions can be excluded (discovered) up to ${g}^{*}\ensuremath{\in}[0.26,0.5]$ (${g}^{*}\ensuremath{\in}[0.43,0.5]$) with ${m}_{T}\ensuremath{\in}[1300\text{ }\text{ }\mathrm{GeV},1950\text{ }\text{ }\mathrm{GeV}]$ (${m}_{T}\ensuremath{\in}[1300\text{ }\text{ }\mathrm{GeV},1520\text{ }\text{ }\mathrm{GeV}]$) with the integrated luminosity of $300\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$. For the high integrated luminosity of $1000\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}(3000\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1})$, the discovered correlated regions can be expanded to ${g}^{*}\ensuremath{\in}[0.3,0.5]$ (${g}^{*}\ensuremath{\in}[0.23,0.5]$) with ${m}_{T}\ensuremath{\in}[1300\text{ }\text{ }\mathrm{GeV},1820\text{ }\text{ }\mathrm{GeV}]$ (${m}_{T}\ensuremath{\in}[1300\text{ }\text{ }\mathrm{GeV},2000\text{ }\text{ }\mathrm{GeV}]$). Besides, we also considered the initial state radiation and beamstrahlung effects and the systematic uncertainty effects of backgrounds, and found that these effects would weaken the excluding or discovery capability.