Forward-backward asymmetries of fourth family fermions through theZ′models at linear colliders

Abstract

We investigate the forward-backward asymmetries in the pair production of fourth-family fermions through the new ${Z}^{\ensuremath{'}}$ interactions in ${e}^{+}{e}^{\ensuremath{-}}$ collisions. A ${Z}^{\ensuremath{'}}$ boson with family-universal couplings can contribute to the pair production of fourth-family fermions via the $s$-channel exchange. Linear colliders provide a clean environment for the physics of the ${Z}^{\ensuremath{'}}$ boson in order to measure its couplings precisely. The effects of the ${Z}^{\ensuremath{'}}$ boson on the asymmetries are shown to be important in some parameter regions for different ${Z}^{\ensuremath{'}}$ models. Among these parameters, the invariant mass distribution ${m}_{F\overline{F}}$ will be an important measurement to constrain the ${Z}^{\ensuremath{'}}$ models. Providing that fourth-family fermions exist in an accesssible mass range, a ${\ensuremath{\chi}}^{2}$ analysis can be used to probe the ${Z}^{\ensuremath{'}}$ models at linear colliders.