Studying the $Wtb$ vertex structure using recent LHC results

The $Wtb$ vertex structure and the search for new anomalous couplings is studied using top quark measurements obtained at the LHC, for a center-of-mass energy of 8 TeV. By combining the latest and most precise results on the single top quark production cross section and the measurements of the $W$-boson helicity fractions ($F_0$ and $F_L$), it is possible to set new limits, at a 95% C.L., on the real and imaginary components of the new couplings. The combination of the LHC observables clearly improves the limits obtained when using the individual results alone. The updated measurements of the $W$-boson helicity fractions and the $s+t$ channels’ electroweak single top quark production, at the Tevatron, improve the LHC limits when a world combination of all observables ($\mathrm{LHC}+\text{Tevatron}$) is performed.

Figure 1

LHC 95% C.L. allowed regions in the planes $[\mathrm{Re}(g_R),\mathrm{Re}(g_L)]$ (left) and $[\mathrm{Re}(V_R),\mathrm{Re}(V_L)]$ (right) from $W$-boson helicity and $t$-channel single top quark production at the LHC, assuming couplings are real.

Figure 2

95% C.L. allowed regions for the $V_R$ (left) and $g_L$ (right) complex couplings from the combination of the $W$-boson helicity and $t$-channel single top quark production measurements at the LHC.

Figure 3

95% C.L. allowed regions for the $g_R$ complex coupling from the combination of the $W$-boson helicity and $t$-channel single top production measurements at the LHC (left) and combining all LHC and Tevatron results (right).