Top quark spin inepcollision

Abstract

We revised the discussion on the degree of spin polarization of single top quarks produced via Wg fusion process in ep collision at TESLA+HERAp and CLIC+LHC energies in connection with our article in [Phys. Rev. D 69, 034016 (2004)]. For $e\stackrel{\ensuremath{\rightarrow}}{b}t\overline{\ensuremath{\nu}}$ subprocess we show that the top quark spin is completely polarized when the spin basis is chosen in the direction of the incoming positron beam in the rest frame of top quark. After combining properly the cross sections of ${e}^{+}\stackrel{\ensuremath{\rightarrow}}{b}t\overline{\ensuremath{\nu}}$ and ${e}^{+}\stackrel{\ensuremath{\rightarrow}}{g}t\overline{b}\overline{\ensuremath{\nu}}$ processes we find that 96% of the top quarks have their spins up in ${e}^{+}$-beam direction with the asymmetry of 0.92. Some of the spin fractions and asymmetries have been corrected 2--5 % when compared to the previous paper. Consequently, this Brief Report improves the results of the previous paper about the ideal basis for studying the top quark spin in ep collision.