Abstract
In this article, we report on the computation of the NLO QCD corrections to ${\rm p}{\rm p} \to \mu^-\bar\nu_{\mu}{\rm e}^+\nu_{\rm e}\bar{\rm b}{\rm b}\bar{\rm b}{\rm b}$ at the LHC, which is an irreducible background to ${\rm p}{\rm p}\to{\rm t}\bar{\rm t}{\rm H}\bigl(\to{\rm b}\bar{\rm b}\bigr)$. This is the first time that a full NLO computation for a $2\to8$ process with 6 external strongly-interacting partons is made public. No approximations are used, and all off-shell and interference effects are taken into account. Cross sections and differential distributions from the full computation are compared to results obtained by using a double-pole approximation for the top quarks. The difference between the full calculation and the one using the double-pole approximation is in general below 5\% but can reach 10\% in some regions of phase space.
Highlights
The physics program of the Large Hadron Collider (LHC) is driven by the measurement of fundamental parameters of the Standard Model (SM) of particle physics
We report on the computation of the next-to-leading order (NLO) QCD corrections to pp → μ−νμeþνebbbb at the LHC, which is an irreducible background to pp → ttHð→ bb Þ
The LO and NLO cross sections obtained from the full computation read σLO 1⁄4 5.203ð4Þþ−3650%% fb and σNLO 1⁄4 10.31ð8Þþ−2118%% fb; ð3:1Þ
Summary
The physics program of the Large Hadron Collider (LHC) is driven by the measurement of fundamental parameters of the Standard Model (SM) of particle physics. Taking into account the top-quark decay products, the complete signal process reads pp → μ−νμeþνebbbb at order Oðα2sα6Þ. The same process receives contributions at order Oðα4sα4Þ, where the bottom–antibottom pair results from a strong interaction. It has been found that theoretical predictions for the background can vary substantially depending on the exact matching and/or parton shower used and tend to overestimate the experimental measurement by 30–50% [30–32] In such predictions, the process is computed with on-shell top quarks, i.e., pp → ttbb , which are subsequently decayed by a parton-shower program. The reason why studies have so far focused on an on-shell description of the top quark is the complexity of the above process [33] It is a 2 → 8 process with 6 external strongly interacting particles and multiple intermediate resonances.
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