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Marco Lopes

Publications and source records attributed to Marco Lopes.

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General Tests for t ---> W+ b couplings at Hadron Colliders

The modularity property of the helicity formalism is used to provide amplitude expressions and stage-two spin-correlation functions which can easily be used in direct experimental searches for electro-weak symmetries and dynamics in the decay processes $t \to W^+ b$, $\bar t \to W^- \bar b$. The formalism is used to describe the decay sequences $t\to W^{+}b\to (l^{+}ν)b$, and $t\to W^{+}b\to (j_{\bar d}j_u)b$. Helicity amplitudes for $t \to W^+ b $ are obtained for the most general $J_{\bar b t}$ current. Thereby, the most general Lorentz-invariant decay-density-matrix for $t\to W^{+}b\to (l^{+}ν)b$, or for $t\to W^{+}b\to (j_{\bar d}j_u)b$, is expressed in terms of eight helicity parameters and, equivalently, in terms of the structures of the $J_{\bar b t}$ current. The parameters are physically defined in terms of partial-width-intensities for polarized-final-states in \newline $t\to W^{+}b$ decay. The full angular distribution for the reactions $q \bar q$ and $g g \to t \bar t \to (W^+ b) (W^- \bar b) \to ...$ can be used to measure these parameters. Since this adds on spin-correlation information from the next stage of decays in the decay sequence, such an energy-angular distribution is called a stage-two spin-correlation (S2SC) function.

hep-ph

Importance of Tests for the Complete Lorentz Structure of the t --> W+ b vertex at Hadron Colliders

The most general Lorentz-invariant decay-density-matrix for $t\to W^{+}b\to (l^{+}ν)b$, or for $t\to W^{+}b\to (j_{\bar d}j_u)b$, is expressed in terms of eight helicity parameters. The parameters are physically defined in terms of partial-width-intensities for polarized-final-states in $t\to W^{+}b$ decay. The parameters are the partial width, the $b$ quark's chirality parameter $ξ$, the $W^+$ polarimetry parameter $σ$, a "pre-SSB" test parameter $ζ$, and four $W_{L}$-$W_{T}$ interference parameters $η$, $η^{'}$, $ω$, $ω^{'}$ which test for $\tilde T_{FS}$ violation. They can be used to test for non-CKM-type CP violation, anomalous $Γ_{L,T}$'s, top weak magnetism, weak electricity, and second-class currents. By stage-two spin-correlation techniques, percent level statistical uncertainites are typical for measurements at the Tevatron, and several mill level uncertainites are typical at the LHC.

hep-ph