The Phenomenology of Single Top Quark Production at the Fermilab Tevatron

TL;DR

This paper analyzes single-top quark production at the Fermilab Tevatron Run II, focusing on the $s$-channel $W^*$ and $t$-channel $W$-gluon fusion modes to study their differential sensitivities to new physics in the top quark sector. It demonstrates how heavy resonances (W') and modified top couplings can differently affect the two channels, and proposes the ratio $R=\sigma_{Wg}/\sigma_{W^*}$ as a model-independent cross-check on $|V_{tb}|$ extractions. The work quantifies theoretical and PDF uncertainties with correlated treatment, derives constraints on FCNC couplings, and discusses the diagnostic power of the production-plane in separating potential new physics scenarios. It also extends the analysis to LHC projections, arguing that the complementary information from the two modes helps distinguish heavy resonances from coupling modifications in the top sector.

Abstract

Single top quark production at the Fermilab Tevatron Run II (a p \bar{p} collider with \sqrt{S} = 2 TeV) proceeds dominantly via two sub-processes, a t-channel W-gluon fusion process, and an s-channel W^* process. We show that these two sub-processes have different sensitivities to new physics effects in the top quark's electro-weak interactions. The W^* process is sensitive to new heavy charged resonances, such as a W' boson, while the W-gluon fusion process is more sensitive to modifications to the top's interaction, including flavor-changing neutral currents involving the top quark. We examine the implications of these results on our ability to measure V_{tb} with confidence, and propose a quantity R = σ_{Wg} / σ_{W^*}, which may be studied in order to characterize the confidence one may place upon a given measurement of V_{tb} from single top production.

Figures (17)

• Figure 1: Feynman diagram for $q \bar{q} \rightarrow W^* \rightarrow t \bar{b}$ at the leading order.
• Figure 2: Representative Feynman diagrams for the $W$-gluon fusion mode of single-top production. The gluon splitting diagram is not really an $\alpha_S$ QCD correction, but rather a 1/${\rm ln}(m_t^2/m_b^2)$ correction coming from the definition of the $b$ PDF. When combining the contributions from these two diagrams, it is necessary to subtract the part in the gluon splitting diagram where the gluon becomes collinear with the $b$ parton, to avoid double counting this region of kinematics.
• Figure 3: Feynman diagrams for $g b \rightarrow t W^{-}$.
• Figure 4: Representative Feynman diagrams for NLO corrections to $q \bar{q} \rightarrow W^* \rightarrow t \bar{b}$ arising from initial state corrections.
• Figure 5: Representative Feynman diagrams for NLO corrections to $q \bar{q} \rightarrow W^* \rightarrow t \bar{b}$ arising from final state corrections.