Ben D. Pecjak

Renormalization-group improved predictions for top-quark pair production at hadron colliders

Precision predictions for phenomenologically interesting observables such as the

Factorization and Momentum-Space Resummation in Deep-Inelastic Scattering

t\bar{t}

Two-loop divergences of massive scattering amplitudes in non-abelian gauge theories

invariant mass distribution and forward-backward asymmetry in top-quark pair production at hadron colliders require control over the differential cross section in perturbative QCD. In this paper we improve existing calculations of the doubly differential cross section in the invariant mass and scattering angle by using techniques from soft-collinear effective theory to perform an NNLL resummation of threshold logarithms, which become large when the invariant mass M of the top-quark pair approaches the partonic center-of-mass energy

Two-loop divergences of QCD scattering amplitudes with massive partons.

\sqrt {{\hat{s}}}

RG-improved single-particle inclusive cross sections and forward-backward asymmetry in

. We also derive an approximate formula for the differential cross section at NNLO in fixed-order perturbation theory, which completely determines the coefficients multiplying the singular plus distributions in the variable

t\bar t

\left( {1 - {{{{M^2}}} \left/ {{\hat{s}}} \right.}} \right)

production at hadron colliders

. We then match our results in the threshold region with the exact results at NLO in fixed-order perturbation theory, and perform a numerical analysis of the invariant mass distribution, the total cross section, and the forward-backward asymmetry. We argue that these are the most accurate predictions available for these observables at present. Using MSTW2008NNLO parton distribution functions (PDFs) along with αs(MZ) = 0.117 and mt = 173.1 GeV, we obtain for the inclusive production cross sections at the Tevatron and LHC the values

The top-pair forward-backward asymmetry beyond NLO

{{{\sigma }}_{\text{Tevatron}}} = \left( {6.30\pm 0.19_{ - 0.23}^{ + 0.31}} \right){\text{pb}}

Precision predictions for the tt¯ production cross section at hadron colliders

and σLHC = (149 ± 7 ± 8) pb, where the first error results from scale variations while the second reflects PDF uncertainties.

Top-quark production and QCD

Renormalization-group methods in soft-collinear effective theory are used to perform the resummation of large perturbative logarithms for deep-inelastic scattering in the threshold region x {yields} 1. The factorization theorem for the structure function F{sub 2}(x,Q{sup 2}) for x {yields} 1 is rederived in the effective theory, whereby contributions from the hard scale Q{sup 2} and the jet scale Q{sup 2}(1 - x) are encoded in Wilson coefficients of effective-theory operators. Resummation is achieved by solving the evolution equations for these operators. Simple analytic results for the resummed expressions are obtained directly in momentum space, and are free of the Landau-pole singularities inherent to the traditional moment-space results. We show analytically that the two methods are nonetheless equivalent order by order in the perturbative expansion, and perform a numerical comparison up to next-to-next-to-leading order in renormalization-group improved perturbation theory.