Understanding single-top-quark production and jets at hadron colliders

TL;DR

This work delivers fully differential NLO predictions for s- and t-channel single-top-quark production with jets, highlighting the crucial role of jet definitions and providing a comprehensive uncertainty assessment. It reveals that jets, not partons, are the correct observables at NLO and demonstrates significant discrepancies between data-driven event generators (PYTHIA/HERWIG) and NLO predictions, especially for final states with extra b-jets. A practical jet-level matching scheme is proposed to bridge fixed-order calculations and showered event samples, enabling more accurate experimental interpretations and CKM element extractions. The results have immediate implications for signal discrimination, background estimation, and future precision top-quark studies at the Tevatron and LHC.

Abstract

I present an analysis of fully differential single-top-quark production plus jets at next-to-leading order. I describe the effects of jet definitions, top-quark mass, and higher orders on the shapes and normalizations of the kinematic distributions, and quantify all theoretical uncertainties. I explain how to interpret next-to-leading-order jet calculations, and compare them to showering event generators. Using the program ZTOP, I show that HERWIG and PYTHIA significantly underestimate both s-channel and t-channel single-top-quark production, and propose a scheme to match the relevant samples to the next-to-leading-order predictions.

Figures (35)

• Figure 1: Representative leading-order Feynman diagrams for (a) $t$-channel, (b) $s$-channel, and (c) $Wt$-associated production of a single top quark. The CKM matrix element $V_{tb}$ appears directly in the production diagrams.
• Figure 2: Transverse momentum $p_{Td}$ of the "$d$"-jet in $t$-channel production at leading and next-to-leading order for the phase space slicing (PSS) and massive dipole formalism (MDF) calculations, and two scales, $m_t$ and the double deep-inelastic-scattering scales ($Q^2$ and $Q^2+m_t^2$). Leading order includes a $K$-factor of $1.09$.
• Figure 3: Transverse momentum $p_{Tj_1}$ of the highest-$p_T$ jet in $t$-channel production at leading and next-to-leading order for different scales.
• Figure 4: Representative leading-order Feynman diagrams for (a) $t$-channel production ($qb\to tq^\prime$), and (b) $W$-gluon fusion ($qg\to t\bar{b}q^\prime$).
• Figure 5: Transverse momentum of the top quark $p_{Tt}$ at LO, NLO, and from the diagram $tbj$, all normalized to the $t$-channel NLO cross section.