Phenomenological studies of top-pair production + jet at NLO
In this talk we discuss top-quark pair production in association with an additional jet. We present numerical results based on a next-to-leading order QCD calculation.
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arXiv subjects
P. Uwer
Publications and source records attributed to P. Uwer.
Top-quark pair production near threshold at LHC
The next-to-leading order analysis for the cross section for hadroproduction of top quark pairs close to threshold is presented. Within the framework of non-relativistic QCD a significant enhancement compared to fixed order perturbation theory is observed which originates from the characteristic remnant of the 1S peak below production threshold of top quark pairs. The analysis includes all color singlet and color octet configurations of top quark pairs in S-wave states and, for the dominant configurations, it employs all-order soft gluon resummation for the hard parton cross section. Numerical results for the Large Hadron Collider at $\sqrt{s} = 14 $TeV and $\sqrt{s} = 10 $TeV and also for the Tevatron are presented. The possibility of a top quark mass measurement from the invariant mass distribution of top quark pairs is discussed.
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Hadronic top-quark pair production in association with a hard jet at next-to-leading order QCD: Phenomenological studies for the Tevatron and the LHC
We report on the calculation of the next-to-leading order QCD corrections to the production of top--antitop-quark pairs in association with a hard jet at the Tevatron and at the LHC. Results for integrated and differential cross sections are presented. We find a significant reduction of the scale dependence. In most cases the corrections are below 20% indicating that the perturbative expansion is well under control. Moreover, the forward--backward charge asymmetry of the top-quark, which is analyzed at the Tevatron, is studied at next-to-leading order. We find large corrections suggesting that the definition of the observable has to be refined.
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Automating dipole subtraction
We report on automating the Catani-Seymour dipole subtraction which is a general procedure to treat infrared divergences in real emission processes at next-to-leading order in QCD. The automatization rests on three essential steps: the creation of the dipole terms, the calculation of the color linked squared Born matrix elements, and the evaluation of different helicity amplitudes. The routines have been tested for a number of complex processes, such as the real emission process gg --> t anti-t ggg.
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Heavy-quark pair production at two loops in QCD
We present updated predictions for the total cross section of top-quark pair production at Tevatron and LHC. For the LHC we also provide results at sqrt(s) = 10 TeV, in view of the anticipated run in 2008 and quote numbers for the production of new heavy-quark pairs with mass in the range 0.5 - 2 TeV. Our two-loop results incorporate all logarithmically enhanced terms near threshold including Coulomb corrections as well as the exact dependence on the renormalization and factorization scale through next-to-next-to-leading order in QCD.
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Top-quark pair + 1-jet production at next-to-leading order QCD
Top-quark pair production with an additional jet is an important signal and background process at the LHC. We present the next-to-leading order QCD calculation for this process and show results for integrated as well as differential cross sections.
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The NLO multileg working group: summary report
This report summarizes the activities of the NLM working group of the Workshop "Physics at TeV Colliders", Les Houches, France, 11-29 June, 2007.
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NLO QCD corrections to WW+jet production at hadron colliders
We report on the calculation of the next-to-leading order QCD corrections to the production of W-boson pairs in association with a hard jet at the Tevatron and the LHC, which is an important source of background for Higgs and new-physics searches. The corrections stabilize the leading-order prediction for the cross section considerably, in particular if a veto against the emission of a second hard jet is applied.
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NLO QCD corrections to t tbar + jet production at hadron colliders
We report on the calculation of the next-to-leading order QCD corrections to the production of top--anti-top quark pairs in association with a hard jet at the Tevatron and at the LHC. We present results for the t tbar + jet cross section and the forward--backward charge asymmetry. The corrections stabilize the leading-order prediction for the cross section. The charge asymmetry receives large corrections.
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Electroweak effects in top-quark pair production at Hadron Colliders
Top-quark physics plays an important role at hadron colliders such as the Tevatron collider at Fermilab or the upcoming Large Hadron Collider (LHC) at CERN. Given the planned experimental precision, detailed theoretical predictions are mandatory. In this article we present analytic results for the complete electroweak corrections to gluon induced top-quark pair production, completing our earlier results for the quark-induced reaction. As an application we discuss top-quark pair production at Tevatron and at LHC. In particular we show that, although small for inclusive quantities, weak corrections can be sizeable for differential distribution.
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Revisiting Bremsstrahlung emission associated with Light Dark Matter annihilations
We compute the single bremsstrahlung emission associated with the pair annihilation of spin-0 particles into electrons and positrons, via the t-channel exchange of a heavy fermion. We compare our result with the work of Beacom et al. . Unlike what is stated in the literature, we show that the Bremsstrahlung cross section is not necessarily given by the tree-level annihilation cross section (for a generalized kinematics) times a factor related to the emission of a soft photon. Such a factorization appears only in the soft photon limit or in the approximation where the masses of the particles in the initial and final states are negligible with respect to the mass of the internal particle. However, in the latter case, we do not recover the same factor as for e^+ e- --> mu^+ mu^- gamma. Numerically the difference, in the hard photon limit, is as large as a factor 3.6. However the effect on the upper limit of the dark matter mass is not significant. Using gamma ray observations, we obtain an upper limit on the dark matter mass of 30 or 100 MeV (depending on the region that is considered for the 511 keV analysis) while Beacom et al. found 20 MeV.
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Electroweak corrections to top-quark pair production in quark--antiquark annihilation
Top-quark physics plays an important role at hadron colliders such as the Tevatron at Fermilab or the LHC at CERN. Given the planned precision at these colliders, precise theoretical predictions are required. In this paper we present the complete electroweak corrections to QCD-induced top-quark pair production in quark--antiquark annihilation. In particular we provide compact analytic expressions for the differential partonic cross section, which will be useful for further theoretical investigations.
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- XSummer - Transcendental Functions and Symbolic Summation in Form
Harmonic sums and their generalizations are extremely useful in the evaluation of higher-order perturbative corrections in quantum field theory. Of particular interest have been the so-called nested sums,where the harmonic sums and their generalizations appear as building blocks, originating for example from the expansion of generalized hypergeometric functions around integer values of the parameters. In this Letter we discuss the implementation of several algorithms to solve these sums by algebraic means, using the computer algebra system Form.
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Investigation of Top quark spin correlations at hadron collider
We report on our results about hadronic $t\bar t$ production at NLO QCD including $t, \bar t$ spin effects, especially on $t\bar t$ spin correlations.
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Top Quark Physics at Colliders
We review some recent developments in top quark production and decay at current and future colliders.
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Top quark pair + jet production at next-to-leading order: NLO QCD corrections to gg -> t tbar g
The reaction pp/pbar p -> t tbar jet+X is an important background process for Higgs boson searches in the mass range below 200 GeV. Apart from that it is also an ideal laboratory for precision measurements in the top quark sector. Both applications require a solid theoretical prediction, which can be achieved only through a full next-to-leading order (NLO) calculation. In this work we describe the NLO computation of the subprocess gg -> t tbar g.
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Les Houches 'Physics at Tev Colliders 2003' QCD/SM Working Group: Summary Report
This report documents the results obtained by the Working Group on Quantum Chromodynamics and the Standard Model for the Workshop `Physics at TeV Colliders'', Les Houches, France, 26 May - 6 June 2003. After a Monte Guide description, the first contributions report on progress in describing multiple interactions, important for the LHC, and underlying events. An announcement of a Monte Carlo database, under construction, is then followed by a number of contributions improving parton shower descriptions. Subsequently, a large number of contributions address resummations in various forms, after which follow studies of QCD effects in pion pair, top quark pair and photon pair plus jet production. After a study of electroweak corrections to hadronic precision observables, the report ends by presenting recent progress in methods to compute finite order corrections at one-loop with many legs, and at two-loop.
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Top quark pair production and decay at hadron colliders
In ongoing and upcoming hadron collider experiments, top quark physics will play an important role in testing the Standard Model and its possible extensions. In this work we present analytic results for the differential cross sections of top quark pair production in hadronic collisions at next-to-leading order in the QCD coupling, keeping the full dependence on the spins of the top quarks. These results are combined with the corresponding next-to-leading order results for the decay of polarized top quarks into dilepton, lepton plus jets, and all jets final states. As an application we predict double differential angular distributions which are due to the QCD-induced top quark spin correlations in the intermediate state. In addition to the analytic results, we give numerical results in terms of fit functions that can easily be used in an experimental analysis.
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