J. Stefan Institute, Jamova 39, P.O. Box 3000, 1001 Ljubljana, Slovenia.
Phys Rev Lett. 2010 Jun 25;104(25):252001. doi: 10.1103/PhysRevLett.104.252001. Epub 2010 Jun 24.
We compute the branching ratios for the rare top quark decays t→cγ and t→cZ mediated by effective flavor changing neutral couplings at next-to-leading order in QCD, including the effects due to operator mixing. After resumming contributions of the order of [α{s}log(Λ/m{t})]{n}, where Λ is the scale at which the effective operators are generated, using renormalization group methods, we compute finite matrix element corrections and study the effects of experimental kinematic cuts on the extracted branching ratios. We find that the t→cγ decay can also be used to probe the effective operators mediating t→cg processes, since the latter can naturally contribute 10% or more to the radiative decay. Conversely, any experimental signal of t→cg would indicate a natural lower bound on t→cZ, γ.
我们在 QCD 的次领头阶计算了由有效味变中性耦合介导的罕见顶夸克衰变 t→cγ 和 t→cZ 的分支比，包括由于算符混合引起的效应。在重整化群方法的帮助下，我们对 α{s}log(Λ/m{t})]{n}阶的贡献进行了重新求和，其中 Λ 是产生有效算符的标度，计算了有限的矩阵元修正，并研究了实验运动学切割对提取分支比的影响。我们发现，t→cγ 衰变也可用于探测介导热子产生过程 t→cg 的有效算符，因为后者可以自然地对辐射衰变贡献 10%或更多。相反，任何 t→cg 的实验信号都会表明 t→cZ，γ 的自然下限。
