Top Quark Pairs In Association Research Articles

Irreducible background and interference effects for Higgs-boson production in association with a top-quark pair

We present an analysis of Higgs-boson production in association with a top-quark pair at the LHC investigating in particular the final state consisting of four b jets, two jets, one identified charged lepton and missing energy. We consider the Standard Model prediction in three scenarios, the resonant Higgs-boson plus top-quark-pair production, the resonant production of a top-quark pair in association with a b-jet pair and the full process including all non-resonant and interference contributions. By comparing these scenarios we examine the irreducible background for the production rate and several kinematical distributions. With standard selection criteria the irreducible background turns out to be three times as large as the signal. For most observables we find a uniform deviation of eight percent between the scenario requiring two resonant top quarks and the full process. In particular phase-space regions the non-resonant contributions cause larger effects, and we observe shape changes for some distributions. Furthermore we investigate interference effects and find that neglecting interference contributions results in an over-estimate of the total cross-section of five percent.

Top-quark mass measurements at LHC: a new approach

We present a new method to measure the top-quark mass in high energetic hadron collisions at the LHC. We study the mass dependence of the production of top-quark pairs in association with an additional jet. The cross section of tt+1Jet production is sensitive to the top-quark mass since gluon radiation depends on the top-quark mass through threshold and cone effects. In particular we study the normalised tt +1Jet cross section differential in the invariant mass of the final state jets. We have investigated the sensitivity of the method together with the impact of various theoretical and experimental uncertainties. We find that the method has the potential to be competitive with existing methods. We emphasize that in the proposed method the mass parameter can be uniquely defined through one-loop renormalization.

Measurements of the Top Quark Pair-Production Cross Section

Measurements of the inclusive and differential cross section for the production of top quark pairs in proton-(anti)proton collision at center-of-mass energies of 1.96, 7.0 and 8.0 TeV are presented and compared with the latest theory predictions and Monte-Carlo models. In addition, first measurements of the production of top quark pairs in association with additional jets or with a boson are highlighted. All measurements are in good agreement with the Standard Model.

Antenna subtraction for the production of heavy particles at hadron colliders

The antenna subtraction method developed originally for the computation of higher order corrections to jet observables from a colourless initial state is extended for hadron collider processes involving a pair of massive particles and jets in the final state at the next-to-leading order (NLO) level. Due to the presence of coloured initial states, the subtraction terms need to be divided into three categories (final-final, initial-final and initial-initial). In this paper, we outline their construction and derive the necessary ingredients: phase space factorisation, antenna functions and also integrated antennae, including the effects of massive final states in all of those building parts. As a first application, we explicitly construct the colour-ordered real radiation and the corresponding antenna subtraction terms required at NLO for the production of a top quark pair and for the production of a top quark pair in association with a hard jet. The latter constitutes an essential ingredient for the computation of the hadronic production of a top-antitop pair at NNLO.

Production of top quark pairs in association with a hard gluon to order $\alpha_s^2$

The production of top quark pairs accompanied by a hard gluon in $e^+e^-$ annihilation is studied including next-to-leading order corrections in the strong coupling. At leading order, the fraction r of $t\bar{t}g$ events with respect to all $t\bar{t}$ events is computed analytically as a function of the minimal gluon energy. Next-to-leading order results for r are given for center-of-mass energies of 0.5 and 1 TeV. We further calculate the differential distribution of r with respect to several variables, including the top quark energy and the $t\bar{t}$ invariant mass. We then investigate how our results depend on the choice of the renormalization scheme for the top quark mass by comparing results expressed in terms of either the pole mass or the $\msbar$ mass. Finally we estimate the sensitivity of the fraction r on the value of the running top quark mass at a scale of 1 TeV.

Production of top quark pairs in association with a hard gluon to order

Production of top quark pairs in association with a hard gluon to order