Single Top Production as a Window to Physics Beyond the Standard Model

TL;DR

This paper argues that single-top production at high-energy hadron colliders provides a direct probe of the W-t-b coupling and potential new physics related to electroweak symmetry breaking.It analyzes three production channels—t-channel W-gluon fusion, s-channel W*, and tW− production—and shows their complementary sensitivity to heavy new particles, top-quark decay properties, and FCNC interactions.Using an effective EWCL framework, it highlights how dimension-4 and dimension-5 operators, plus potential new scalars and gauge bosons, could modify cross sections and be constrained by collider data, with polarization observables offering additional discriminatory power.The work concludes that a combined analysis of the three channels and top polarization can reveal the nature of new physics in the top sector and test the SM picture of electroweak symmetry breaking.

Abstract

Production of single top quarks at a high energy hadron collider is studied as a means to identify physics beyond the standard model related to the electroweak symmetry breaking. The sensitivity of the $s$-channel $W^*$ mode, the $t$-channel $W$-gluon fusion mode, and the \tw mode to various possible forms of new physics is assessed, and it is found that the three modes are sensitive to different forms of new physics, indicating that they provide complimentary information about the properties of the top quark. Polarization observables are also considered, and found to provide potentially useful information about the structure of the interactions of top.

Figures (20)

• Figure 1: Feynman diagrams for $t$-channel production of a single top in the SM.
• Figure 2: Feynman diagram for $s$-channel production of a single top in the SM.
• Figure 3: Feynman diagrams for $t \, W^-~$ production in the SM.
• Figure 4: Feynman diagram for $s$-channel production of a single top and a $b^\prime$: $q \, \bar{q}^\prime \rightarrow t \, \bar{b}^\prime$.
• Figure 5: The NLO rates (in pb) for the process $q \, \bar{q}^\prime \rightarrow W^* \rightarrow t \, \bar{b}^\prime$ for various $b^\prime$ masses at the Tevatron (solid curve) and LHC (dashed curve), assuming $V_{tb^\prime}= 1$. At the Tevatron, the rates of $q \, \bar{q}^\prime \rightarrow W^* \rightarrow \bar{t} \, b^\prime$ is equal to the $t \, \bar{b}^\prime$ rate. The $\bar{t} \, b^\prime$ rate at the LHC is shown as the dotted curve.