We present a program to calculate the total cross section for top-quark pair production in hadronic collisions. The program takes into account recent theoretical developments such as approximate ...next-to-next-to-leading order perturbative QCD corrections and it allows for studies of the theoretical uncertainty by separate variations of the factorization and renormalization scales. In addition it offers the possibility to obtain the cross section as a function of the running top-quark mass. The program can also be applied to a hypothetical fourth quark family provided the QCD couplings are standard.
Program title: Hathor
Catalogue identifier: AEID_v1_0
Program summary URL:
http://cpc.cs.qub.ac.uk/summaries/AEID_v1_0.html
Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland
Licensing provisions: GNU GPL 3
No. of lines in distributed program, including test data, etc.: 5405
No. of bytes in distributed program, including test data, etc.: 327 718
Distribution format: tar.gz
Programming language: C++, Fortran, Java
Computer: Standard PCs (x86, x86_64 processors)
Operating system: Linux
RAM: 256 MB
Classification: 11.1
External routines: Interface to LHAPDF for the user's choice of parton distribution functions, see
http://projects.hepforge.org/lhapdf/
Nature of problem: Computation of total cross section in perturbative QCD.
Solution method: Numerical integration of hard parton cross section convoluted with parton distribution functions.
Running time: A few seconds to a few minutes on standard desktop PCs or notebooks, depending on the chosen options.
Weak corrections for top-quark pair production at hadron colliders are revisited. Predictions for collider energies of 8 TeV, adopted to the recent LHC run, and for 13 as well as 14 TeV, presumably ...relevant for the next round of LHC experiments, are presented. Kinematic regions with large momentum transfer are identified, where the corrections become large and may lead to strong distortions of differential distributions, thus mimicking anomalous top-quark couplings. As a complementary case we investigate the threshold region, corresponding to configurations with small relative velocity between top and antitop quarks, which is particularly sensitive to the top-quark Yukawa coupling. We demonstrate, that nontrivial upper limits on this coupling, complementary to those recently derived by the CMS and the ATLAS collaborations, are well within reach of ongoing experiments. We, furthermore, suggest a prescription that allows the implementation of these corrections in current Monte Carlo generators. Furthermore, the weak corrections have been included in the publicly available hathor library. The numerical results presented in this article use the same setup as the recently calculated next-to-next-to-leading-order QCD corrections. The results can thus be combined to give the most precise theoretical predictions.
We present updated predictions for single top-quark production in hadronic collisions. The analysis is based on next-to-leading order QCD calculations. The input parameters are fixed to recent ...measurements. We compare different PDF sets and investigate the related uncertainties. The impact of uncalculated higher orders is estimated using an independent variation of the renormalisation and factorisation scale. The theoretical predictions are compared with recent measurements from Tevatron and LHC. Furthermore, the cross section measurements are used to estimate the top-quark mass. To perform the analysis we extended the publicly available HatHor program to single top-quark production. We thus provide a unified framework for the fast numerical evaluation of total cross sections for top-quark production, which may be used for example in Standard Model fits. For future extensions towards NNLO accuracy, we include already all scale dependent terms at NNLO. We briefly describe how to use the program and provide all required tools to repeat the aforementioned analysis.
We present a computer library for the numerical evaluation of colour-ordered n-gluon amplitudes at one-loop order in pure Yang–Mills theory. The library uses the recently developed technique of ...generalised unitarity. Running in double precision the library yields reliable results for up to 14 gluons with only a small fraction of events requiring a re-evaluation using extended floating point arithmetic. We believe that the library presented here provides an important contribution to future LHC phenomenology. The program may also prove useful in cross checking results obtained by other methods. In addition, the code provides a sample implementation which may serve as a starting point for further developments.
Program title:NGluon
Catalogue identifier: AEIZ_v1_0
Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEIZ_v1_0.html
Program obtainable from: CPC Program Library, Queenʼs University, Belfast, N. Ireland
Licensing provisions: GNU Public License
No. of lines in distributed program, including test data, etc.: 30 677
No. of bytes in distributed program, including test data, etc.: 334 896
Distribution format: tar.gz
Programming language: C++
Computer: Any computer platform supported by the GNU compiler suite.
Operating system: No specific requirements – tested on Scientific Linux 5.2.
RAM: Depending on the complexity, for realistic applications like 10 gluon production in double precision below 10 MB.
Classification: 11.5
External routines: QCDLoop (http://qcdloop.fnal.gov/), qd (http://crd.lbl.gov/~dhbailey/mpdist/)
Nature of problem: Evaluation of next-to-leading order corrections for gluon scattering amplitudes in pure gauge theory.
Solution method: Purely numerical approach based on tree amplitudes obtained via Berends–Giele recursion combined with unitarity method.
Restrictions: Running in double precision the number of gluons should not exceed 14.
Running time: Depending on the number of external gluons between less than a millisecond (4 gluons) up to a 1 s (14 gluons) per phase space point.
► We present a c++ code computing one-loop multi-gluon amplitudes in Yang–Mills. ► We use newly developed generalised unitarity methods for a fast implementation. ► An arbitrary number of gluons can be computed using multiple precision. ► Results are numerically stable in double precision for <14 gluons.
A new method to measure the top-quark mass in high energetic hadron collisions is presented. We use theoretical predictions calculated at next-to-leading order accuracy in quantum chromodynamics to ...study the (normalized) differential distribution of the
cross section with respect to its invariant mass
. The sensitivity of the method to the top-quark mass together with the impact of various theoretical and experimental uncertainties has been investigated and quantified. The new method allows for a complementary measurement of the top-quark mass parameter and has a high potential to become competitive in precision with respect to established approaches. Furthermore we emphasize that in the proposed method the mass parameter is uniquely defined through one-loop renormalization.
We report on the calculation of the next-to-leading-order QCD corrections to the production of top-quark-top-antiquark pairs in association with a hard jet at the Fermilab Tevatron and the CERN Large ...Hadron Collider. We present results for the ttover +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.
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 paper we discuss the implementation of several algorithms to solve these sums by algebraic means, using the computer algebra system
Form.
Title of program:
XSummer
Catalogue identifier:ADXQ_v1_0
Program summary URL:
http://cpc.cs.qub.ac.uk/summaries/ADXQ_v1_0
Program obtainable from:CPC Program Library, Queen's University of Belfast, N. Ireland
License:GNU Public License and
Form License
Computers:all
Operating system:all
Program language:
Form
Memory required to execute:Depending on the complexity of the problem, recommended at least 64 MB RAM
No. of lines in distributed program, including test data, etc.:9854
No. of bytes in distributed program, including test data, etc.:126 551
Distribution format:tar.gz
Other programs called:none
External files needed:none
Nature of the physical problem:Systematic expansion of higher transcendental functions in a small parameter. The expansions arise in the calculation of loop integrals in perturbative quantum field theory.
Method of solution:Algebraic manipulations of nested sums.
Restrictions on complexity of the problem:Usually limited only by the available disk space.
Typical running time:Dependent on the complexity of the problem.
We investigate the production of heavy, neutral Higgs boson resonances and their decays to top-quark top-antiquark (tt) pairs at the Large Hadron Collider (LHC) at next-to-leading order (NLO) in the ...strong coupling of quantum chromodynamics (QCD). The NLO corrections to heavy Higgs boson production and the Higgs-QCD interference are calculated in the large m sub(t)limit with an effective K-factor rescaling. The nonresonant tt background is taken into account at NLO QCD including weak-interaction corrections. In order to consistently determine the total decay widths of the heavy Higgs bosons, we consider for definiteness the type-II two-Higgs-doublet extension of the standard model and choose three parameter scenarios that entail two heavy neutral Higgs bosons with masses above the tt threshold and unsuppressed Yukawa couplings to top quarks. For these three scenarios we compute, for the LHC operating at 13 TeV, the tt cross section and the distributions of the tt invariant mass, of the transverse top-quark momentum and rapidity, and of the cosine of the Collins-Soper angle with and without the two heavy Higgs resonances. For selected M sub(t)tbins we estimate the significances for detecting a heavy Higgs signal in the tt dileptonic and lepton plus jets decay channels.
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.
We study the QCD corrections at next-to-next-to-leading order (NNLO) to the cross section for the hadronic pair-production of top quarks. We present new results in the high-energy limit using the ...well-known framework of kt-factorization. We combine these findings with the known threshold corrections and present improved approximate NNLO results over the full kinematic range. This approach is employed to quantify the residual theoretical uncertainty of the approximate NNLO results which amounts to about 4% for the Tevatron and 5% for the LHC cross section predictions. Our analytic results in the high-energy limit will provide an important check on future computations of the complete NNLO cross sections.
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