Single top quarks at the Fermilab Tevatron

TL;DR

The paper computes tree‑level cross sections for all electroweak single‑top production modes at the Fermilab Tevatron, examining dependencies on $m_t$, parton distributions, $Q^2$, and collider energy. It provides detailed kinematic distributions to aid mode separation and investigates potential nonstandard $Wtb$ couplings through $V_{tb}$ sensitivity and top polarization. The authors quantify uncertainties, propose methods to avoid double counting, and project Run‑2/Run‑3 prospects for measuring $V_{tb}$, the $Wtb$ structure, and the top quark partial width, highlighting the phenomenological relevance of single‑top production as a direct probe of the electroweak top‑quark sector. The results underscore the Tevatron’s potential to test the Standard Model Wtb vertex and extract fundamental parameters in a challenging, background‑rich environment.

Abstract

We present a calculation of the single top quark cross section for proton-antiproton interactions with sqrt(s) = 1.8 TeV at the Fermilab Tevatron collider. We examine the effects of top mass, parton distribution functions, QCD scale, and collision energy, on each of the component production mechanisms, and study the kinematic distributions for standard model electroweak production. At the upgraded Tevatron with sqrt(s) = 2.0 TeV and high luminosity, it will be possible to test the nature of the Wtb coupling using single top production. We estimate the sensitivity to measure the single top cross section, and thus to directly measure V_tb and the top quark partial width. We show what happens to the V_tb measurement when an anomalous (V+A) component is added to the Wtb coupling, and how the top quark polarization affects the kinematic distributions.

Figures (11)

• Figure 1: Representative Feynman diagrams for the three single top quark production processes at the Fermilab Tevatron: (a) the $W^*$ s-channel process ${\hbox{${p\bar{p}}$}}{\hbox{$\rightarrow$}}t{\hbox{${\bar{b}}$}}+X$; (b) the $W$ t- and u-channel process ${\hbox{${p\bar{p}}$}}{\hbox{$\rightarrow$}}tq+X$, including subprocess 2.2, $W$-gluon fusion; and (c) ${\hbox{${p\bar{p}}$}}{\hbox{$\rightarrow$}}tW^-+X$.
• Figure 2: Single top quark cross sections at the Tevatron with $\sqrt{s}=1.8$ TeV, versus top quark mass: (a) s-channel $W^*$ production ${\hbox{${p\bar{p}}$}}{\hbox{$\rightarrow$}}t{\hbox{${\bar{b}}$}}+t{\hbox{${\bar{b}}$}}q$; (b) t- and u-channel production ${\hbox{${p\bar{p}}$}}{\hbox{$\rightarrow$}}tq+tq{\hbox{${\bar{b}}$}}$; (c) ${\hbox{${p\bar{p}}$}}{\hbox{$\rightarrow$}}tW+tW{\hbox{${\bar{b}}$}}$; and (d) the total single top and antitop cross section ${\hbox{${p\bar{p}}$}}{\hbox{$\rightarrow$}}t+{\hbox{${\bar{t}}$}}+X$. The resummed next-to-leading order ${\hbox{${t\bar{t}}$}}$ cross section of Ref. berger is shown as the uppermost line in (d), for comparison with single top production (at leading order).
• Figure 3: Single top quark cross sections ($m_t=180$ GeV, $\sqrt{s}=1.8$ TeV) versus QCD evolution scale $Q^2$ for: (a) s-channel $W^*$ production ${\hbox{${p\bar{p}}$}}{\hbox{$\rightarrow$}}t{\hbox{${\bar{b}}$}}+t{\hbox{${\bar{b}}$}}q$; (b) t- and u-channel production ${\hbox{${p\bar{p}}$}}{\hbox{$\rightarrow$}}tq+tq{\hbox{${\bar{b}}$}}$; (c) ${\hbox{${p\bar{p}}$}}{\hbox{$\rightarrow$}}tW+tW{\hbox{${\bar{b}}$}}$; and (d) the summed single top and antitop cross section ${\hbox{${p\bar{p}}$}}{\hbox{$\rightarrow$}}t+{\hbox{${\bar{t}}$}}+X$.
• Figure 4: Single top produced together with a light quark, $q'b{\rightarrow}tq$, from an initial state sea $b$ quark, showing the cross section before and after subtraction of the gluon splitting term, as a function of: (a) top quark mass (with $Q^2=m_t^2$); and (b) scale $Q^2$ (with $m_t=180$ GeV).
• Figure 5: Single top quark cross section plotted (a) versus top quark mass, at four production energies: the Fermilab Tevatron at $\sqrt{s}=1.8$ TeV; the upgraded Tevatron at 2.0 TeV; the proposed TeV* collider at 4.0 TeV; and the CERN $pp$ Large Hadron Collider at 14 TeV. Plot (b) shows the cross section versus collider energy (with $m_t=180$ GeV), for each of the single top production mechanisms. The values in (b) up to 12 TeV are for ${\hbox{${p\bar{p}}$}}$ production, whereas the results at 14 TeV are for $pp$ collisions.