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, f1^L, f1^R, f2^L and f2^R. We further introduce a set of parameters x0, xm, xp and x5 which exhibit a linear relation to the single top production cross sections. Using recent data for the t-channel single top production cross section at, tW associated production cross section crtw, s-channel single top production cross section δs, and W-helicity fractions F0, FL and FR collected at the 8 TeV LHC and Tevatron, we perform a global fit to impose constraints on the top quark effective couplings. Our globM fitting results show that the top quark effective couplings are strongly correlated. We show that （i） improving the measurements of δt and δtw is important in constraining the correlation of （f1^R, f2^R） and （f2^L,f2^R）; （ii） f1^L and f2^R are anti-correlated, and are sensitive to all the four experiments; （iii） f1^R and f2^L are also anti-correlated, and are sensitive to the F0 and FL measurements; （iv） the correlation between f2^L and f2^R is sensitive to the precision of the δt, δtw and F0 measurements. The effective Wtb couplings are studied in three kinds of new physics models： the G（221） = SU（2）1 SU（2）2 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 （Mw,） is less than several hundred GeV, but the constraint is loose if Mw^t 〉 1 TeV. Fhrthermore, 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.