A general analysis of Wtb anomalous couplings

We investigate new physics effects on the Wtb effective couplings in a model-independent framework. The new physics effects can be parametrized by four independent couplings, f(1)(L), f(1)(R), f(2)(L) and f(2)(R). We further introduce a set of parameters x(0), x(m), x(p) and x(5) which exhibit a linear relation to the single top production cross sections. Using recent data for the t-channel single top production cross section sigma(t), tW associated production cross section sigma(tw), s-channel single top production cross section sigma(s), and W-helicity fractions F-0, F-L and F-R collected at the 8 TeV LHC and Tevatron, we perform a global fit to impose constraints on the top quark effective couplings. Our global fitting results show that the top quark effective couplings are strongly correlated. We show that (i) improving the measurements of sigma(t) and sigma(tw) is important in constraining the correlation of (f(1)(R),f(2)(R)) and (f(2)(L),f(2)(R)); (ii) f(1)(L) and f(2)(R) are ant-correlated, and are sensitive to all the four experiments; (iii) f(1)(R) and f(2)(L) are also anti-correlated, and are sensitive to the F-0 and F-L measurements; (iv) the correlation between f(2)(L) and f(2)(R) is sensitive to the precision of the sigma(t), sigma(tW) and F-0 measurements. The effective Wtb couplings are studied in three kinds of new physics models: the G(221) = SU(2)(1)circle times SU(2)(2)circle times U(1)(x) models, the vector-like quark models and the Littlest Higgs model with and without T-parity. We show that the Wtb couplings in the left-right model and the un-unified model are sensitive to the ratio of gauge couplings when the new heavy gauge boson's mass (M-w') is less than several hundred GeV, but the constraint is loose if M-w' > 1 TeV. Furthermore, the Wtb couplings in vector-like quark models and the Littlest Higgs models are sensitive to the mixing angles of new heavy particles and SM particles.