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Top Pair Production Beyond Double-Pole Approximation: pp, pp~ --> 6 Fermions and 0, 1 or 2 Additional Partons

N. Kauer

TL;DR

The work addresses the accuracy of predicting ttbar production with up to two additional jets at hadron colliders by computing complete LO matrix elements and comparing them with NWA and DPA; it evaluates three finite-width schemes (FWS, CMS, OFS) and demonstrates that sub- and non-resonant amplitudes can boost cross sections by 5–8% at the LHC and VLHC while leaving DPA/NWA differences at about 1% or less. The study quantifies how these effects propagate to backgrounds for SM Higgs searches and Beyond-SM scenarios, finding substantial background enhancements (up to ~1.8×) under certain cuts and channels, with OFS sometimes underestimating the cross sections. The results highlight the need for full amplitude calculations in precision background modeling, suggest that LO uncertainties remain large but ratios are robust, and point toward future NLO extensions and standard interfaces to parton showers and detector simulations. The authors also provide a framework, OmniComp, for distributed Monte Carlo integration and plan to release the complete LO ttbar+jets program to the community.

Abstract

Hadron collider cross sections for tt~ production and di-lepton, single-lepton and all-jet decays with up to 2 additional jets are calculated using complete LO matrix elements with 6-, 7- and 8-particle final states. The fixed-width, complex-mass and overall-factor schemes (FWS, CMS & OFS) are employed and the quality of narrow-width and double-pole approximations (NWA & DPA) is investigated for inclusive production and suppressed backgrounds to new particle searches. NWA and DPA cross sections differ by 1% or less. The inclusion of sub- and non-resonant amplitudes effects a cross section increase of 5-8% at pp supercolliders, but only minor changes at the Tevatron. On-shell tt~/Wtb backgrounds for the H --> WW decay in weak boson fusion, the hadronic τdecay of a heavy H^\pm and the φ--> hh --> ττbb~ radion decay at the LHC are updated, with corrections ranging from 3% to 30%. FWS and CMS cross sections are uniformly consistent, but OFS cross sections are up to 6% smaller for some backgrounds.

Top Pair Production Beyond Double-Pole Approximation: pp, pp~ --> 6 Fermions and 0, 1 or 2 Additional Partons

TL;DR

The work addresses the accuracy of predicting ttbar production with up to two additional jets at hadron colliders by computing complete LO matrix elements and comparing them with NWA and DPA; it evaluates three finite-width schemes (FWS, CMS, OFS) and demonstrates that sub- and non-resonant amplitudes can boost cross sections by 5–8% at the LHC and VLHC while leaving DPA/NWA differences at about 1% or less. The study quantifies how these effects propagate to backgrounds for SM Higgs searches and Beyond-SM scenarios, finding substantial background enhancements (up to ~1.8×) under certain cuts and channels, with OFS sometimes underestimating the cross sections. The results highlight the need for full amplitude calculations in precision background modeling, suggest that LO uncertainties remain large but ratios are robust, and point toward future NLO extensions and standard interfaces to parton showers and detector simulations. The authors also provide a framework, OmniComp, for distributed Monte Carlo integration and plan to release the complete LO ttbar+jets program to the community.

Abstract

Hadron collider cross sections for tt~ production and di-lepton, single-lepton and all-jet decays with up to 2 additional jets are calculated using complete LO matrix elements with 6-, 7- and 8-particle final states. The fixed-width, complex-mass and overall-factor schemes (FWS, CMS & OFS) are employed and the quality of narrow-width and double-pole approximations (NWA & DPA) is investigated for inclusive production and suppressed backgrounds to new particle searches. NWA and DPA cross sections differ by 1% or less. The inclusion of sub- and non-resonant amplitudes effects a cross section increase of 5-8% at pp supercolliders, but only minor changes at the Tevatron. On-shell tt~/Wtb backgrounds for the H --> WW decay in weak boson fusion, the hadronic τdecay of a heavy H^\pm and the φ--> hh --> ττbb~ radion decay at the LHC are updated, with corrections ranging from 3% to 30%. FWS and CMS cross sections are uniformly consistent, but OFS cross sections are up to 6% smaller for some backgrounds.

Paper Structure

This paper contains 7 sections, 9 equations, 1 figure, 6 tables.

Table of Contents

  1. Introduction
  2. Program Description
  3. Numerical Results
  4. Inclusive Production
  5. Backgrounds to SM Higgs Searches
  6. Backgrounds to Beyond-SM Physics Searches
  7. Summary and Outlook

Figures (1)

  • Figure 1: Charged lepton separation in $\eta$-$\phi$ space and transverse mass distributions for suppressed $t\bar{t}$ production and di-lepton decay ($b\bar{b}\: e^+ \nu_e\:\mu^- \bar{\nu}_\mu$) at the LHC. The applied central jet veto ($p_T > 15$ GeV and $|\eta| < 3.2$) reduces the $t\bar{t}$ acceptance to $4\times10^{-3}$. Differential cross sections with complete matrix elements (solid lines) and in NWA and DPA (dashed lines) are shown. Sub- and non-resonant amplitude contributions enhance the total cross section by a factor 1.8. Off-shell top effects (DPA v. NWA) and deviations between finite-width schemes (FWS, CMS, OFS) are negligible. The transverse mass is defined as $m_T = \sqrt{2p_T^{\ell\ell}=\hbox{$E$}E \hbox{/} _T[1-\cos\Delta\theta(\ell\ell,=\hbox{$E$}E \hbox{/} _T)]}$.