QCD corrections to top quark pair production in association with a photon at hadron colliders

Abstract

We compute QCD corrections to the production of a tt pair in association with a hard photon at the Tevatron and the LHC. This process allows a direct measurement of the top quark electromagnetic couplings that, at the moment, are only loosely constrained. We include top quark decays, treating them in the narrow width approximation, and retain spin correlations of final-state particles. Photon radiation off top quark decay products is included in our calculation and yields a significant contribution to the cross-section. We study next-to-leading order QCD corrections to the pp → ttγ process at the Tevatron for the selection criteria used in a recent measurement by the CDF collaboration. We also discuss the impact of QCD corrections to the pp → ttγ process on the measurement of the top quark electric charge at the 14 TeV LHC.2

One-loop calculations in quantum field theory: From Feynman diagrams to unitarity cuts

“…This implies that the two vertices are 103) or consequently that both l 0 3 = 0 and l 0 4 = 0 which cannot simultaneously be satisfied for generic external momenta p 3 and p 4 . This helicity amplitude thus has a vanishing contribution to the coefficient of this box integral.…”

“…[24]; we also note that all aspects of the following discussion have been checked in realistic computations of NLO QCD corrections to top quark pair production reported in Refs. [71,72,103]. Analytic computations of one-loop helicity amplitudes for tt production within generalized unitarity framework can be found in [106].…”

Search for top squarks in final states with one isolated lepton, jets, and missing transverse momentum ins=13 TeVppAaboud1, Bergeås2, Brenner3 et al. 2016Phys. Rev. D540320View full textAdd to dashboardCite

“…Both of these differences are mitigated if the boson p T is larger than the Z boson mass. In this limit, the impact of the mass difference on the available phase space is reduced and the rate of photon radiation from bremsstrahlung is suppressed [87]. This small fraction of photons is fully accounted for in the simulation and any uncertainty in their modeling is subdominant compared to the uncertainties described in Sec.…”

“…The tt þ Z sample uses the default P m T scale and is generated with up to two partons. The top decay is performed in MG5_AMC for tt þ γ to account for hard photon radiation from the top decay products, which is an ∼15% effect for p γ T ∼ 120 GeV [87].…”

Search for Supersymmetry in pp Collisions at √s = 8 TeV with a Photon, Lepton, and Missing Transverse Energy

“…The cross section is taken from literature [97,98] when available. For the ttγ sample, a kfactor of 2.0 [99] is applied to the cross section calculated by the generator. For WW and WZ samples, NLO cross sections calculated by mcfm are used.…”