Isolating Wt production at the LHC

TL;DR

Isolating Wt production at the LHC is challenging due to interference with tt̄. The paper assesses whether Wt can be treated as a separate production channel using MC@NLO with DR and DS definitions, demonstrating that with realistic signal-isolation cuts the interference is small and the Wt signal stands above tt̄ uncertainties. It also examines Wt as a background to Higgs → WW and demonstrates DR/DS agreement, supporting separate background treatment. A cross-check with a fixed-order WWbb tree-level approach shows that simple rescalings fail to capture NLO effects, underscoring the advantages of MC@NLO for accurate background modeling. The work provides practical guidance for modeling top-quark backgrounds in LHC analyses and for applying DR/DS as systematic checks across related processes.

Abstract

We address the issue of single top production in association with a W boson at the Large Hadron Collider, in particular how to obtain an accurate description in the face of the top pair production background given that the two processes interfere with each other. We stress the advantages of an MC@NLO description, and find that for cuts used to isolate the signal, it makes sense to consider Wt as a well-defined production process in that the interference with top pair production is small, and the cross-section of the former is above the scale variation uncertainty associated with the latter. We also consider the case where both Wt and top pair production are backgrounds to a third process (Higgs boson production followed by decay to a W boson pair), and find in this context that interference issues can also be neglected. We discuss the generalization of our results to other situations, aided by a comparison between the MC@NLO approach and a calculation of the WWbb final state matched to a parton shower.

Figures (17)

• Figure 1: The three SM single top production modes, shown at LO: (1) $s$-channel production; (2) $t$-channel production; (3) $Wt$ production. Double lines represent the top quark.
• Figure 2: A subset of diagrams contributing to $Wt$ production at NLO, consisting of top pair production, with weak decay of one of the final state top particles.
• Figure 3: The transverse momentum (a) and pseudo-rapidity (b) distributions of the light jets in $Wt$ production (subject to the cuts outlined in the text), shown for both diagram removal (DR) and diagram subtraction (DS). The $b$-tagging efficiency and light jet rejection rate are given by $e_b=0.6$ and $r_{lj}$=30 respectively. Uncertainties are statistical, and the vertical axis has arbitrary normalization.
• Figure 4: The transverse momentum (a) and pseudo-rapidity (b) distributions of the hard $b$ jet in $Wt$ production (subject to the cuts outlined in the text), shown for both diagram removal (DR) and diagram subtraction (DS). The $b$-tagging efficiency and light jet rejection rate are given by $e_b=0.6$ and $r_{lj}$=30 respectively. Uncertainties are statistical, and the vertical axis has arbitrary normalization.
• Figure 5: The transverse momentum (a) and pseudo-rapidity (b) distributions of the isolated lepton in $Wt$ production (subject to the cuts outlined in the text), shown for both diagram removal (DR) and diagram subtraction (DS). The $b$-tagging efficiency and light jet rejection rate are given by $e_b=0.6$ and $r_{lj}$=30 respectively. Uncertainties are statistical, and the vertical axis has arbitrary normalization.