P. Uwer

Humboldt-Universität zu Berlin, Berlín, Berlin, Germany

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Publications (102)161.25 Total impact

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    ABSTRACT: This report summarizes the proceedings of the 2014 Mainz Institute for Theoretical Physics (MITP) scientific program on "High precision fundamental constants at the TeV scale". The two outstanding parameters in the Standard Model dealt with during the MITP scientific program are the strong coupling constant $\alpha_s$ and the top-quark mass $m_t$. Lacking knowledge on the value of those fundamental constants is often the limiting factor in the accuracy of theoretical predictions. The current status on $\alpha_s$ and $m_t$ has been reviewed and directions for future research have been identified.
    05/2014;
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    ABSTRACT: In these proceedings we report our progress in the development of the publicly available C++ library NJet for accurate calculations of high-multiplicity one-loop amplitudes. As a phenomenological application we present the first complete next-to-leading order (NLO) calculation of five jet cross section at hadron colliders.
    12/2013;
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    ABSTRACT: This work presents a new method to measure the top-quark mass in hadronic collisions[1]. The method uses the sensitivity of the tbar t + 1-jet production on the top-quark mass. In detail we study the ℛ distribution defined as the tbar t + 1-jet normalized cross section differential in the invariant mass of the total system and calculated at NLO accuracy. We prove that the ℛ distribution has a high sensitivity to the top-quark mass. Furthermore we investigate and quantify the impact of the dominant theoretical and experimental uncertainties. The results obtained show, that the method has the potential to be competitive in precision with established approaches and allows a complementary measurement of the top-quark mass at hadron colliders. We emphasize that in the proposed method the mass parameter is uniquely defined through one-loop renormalization.
    11/2013;
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    ABSTRACT: We present theoretical predictions for five jet production in proton-proton collisions at next-to-leading order accuracy in QCD. Inclusive as well as differential observables are studied for collision energies of 7 and 8 TeV. In general the next-to-leading order corrections stabilize the theoretical predictions with respect to scale variations. In case of the inclusive jet cross sections, we compare with experimental data where possible and find reasonable agreement. We observe that the four-to-three and five-to-four jet ratios show better perturbative convergence than the known three-to-two ratio and are promising candidates for future alpha_s measurements. Furthermore, we present a detailed analysis of uncertainties related to parton distribution functions. The full colour virtual matrix elements used in the computation were obtained with the NJet package, a publicly available library for the evaluation of one-loop amplitudes in massless QCD.
    09/2013; 89(3).
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    ABSTRACT: We present an update of the Binoth Les Houches Accord (BLHA) to standardise the interface between Monte Carlo programs and codes providing one-loop matrix elements.
    08/2013;
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    ABSTRACT: 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.
    Journal of Physics Conference Series 07/2013; 452(1):2050-.
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    ABSTRACT: Weak corrections for top-quark pair production at hadron colliders are revisited. Predictions for collider energies of 8 TeV, adopted to the present LHC run, and for 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 quark, which is particularly sensitive to the top-quark Yukawa coupling. We demonstrate, that nontrivial upper limits on this coupling are well within reach of ongoing experiments.
    05/2013;
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    ABSTRACT: Abstract: 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.
    European Journal of Physics 03/2013; c(73). · 0.64 Impact Factor
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    ABSTRACT: We study three and four jet production in hadronic collisions at next-to-leading order accuracy in massless QCD. We cross check results previously obtained by the BlackHat collaboration for the LHC with a centre-of-mass energy of sqrt(s)=7 TeV and present new results for the LHC operating at 8 TeV. We find large negative NLO corrections reducing the leading-order cross sections by about 40-50%. Furthermore we observe an important reduction of the scale uncertainty. In addition to the cross sections we also present results for differential distributions. The dynamical renormalization/factorization scale used in the calculation leads to a remarkably stable K-factor. The results presented here were obtained with the NJet package, a publicly available library for the evaluation of one-loop amplitudes in massless QCD.
    Physics Letters B 09/2012; 718(3). · 4.57 Impact Factor
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    ABSTRACT: We present a C++ library for the numerical evaluation of one-loop virtual corrections to multi-jet production in massless QCD. The pure gluon primitive amplitudes are evaluated using NGluon. A generalized unitarity reduction algorithm is used to construct arbitrary multiplicity fermion-gluon primitive amplitudes. From these basic building blocks the one-loop contribution to the squared matrix element, summed over colour and helicities, is calculated. No approximation in colour is performed. While the primitive amplitudes are given for arbitrary multiplicities we provide the squared matrix elements only for up to 7 external partons allowing the evaluation of the five jet cross section at next-to-leading order accuracy. The library has been recently successfully applied to four jet production at next-to-leading order in QCD.
    Computer Physics Communications 09/2012; 184(8). · 2.41 Impact Factor
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    ABSTRACT: Recent advances in our understanding of tree-level QCD amplitudes in the massless limit exploiting an effective (maximal) supersymmetry have led to the complete analytic construction of tree-amplitudes with up to four external quark-anti-quark pairs. In this work we compare the numerical efficiency of evaluating these closed analytic formulae to a numerically efficient implementation of the Berends-Giele recursion. We compare calculation times for tree-amplitudes with parton numbers ranging from 4 to 25 with no, one, two and three external quark lines. We find that the exact results are generally faster in the case of MHV and NMHV amplitudes. Starting with the NNMHV amplitudes the Berends-Giele recursion becomes more efficient. In addition to the runtime we also compared the numerical accuracy. The analytic formulae are on average more accurate than the off-shell recursion relations though both are well suited for complicated phenomenological applications. In both cases we observe a reduction in the average accuracy when phase space configurations close to singular regions are evaluated. We believe that the above findings provide valuable information to select the right method for phenomenological applications.
    Physical review D: Particles and fields 06/2012;
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    ABSTRACT: We present heavy-flavor production in association with one jet in hadronic collisions matched to parton shower Monte Carlo predictions at next-to-leading order QCD with account of top-quark decays and spin correlations. We use the POWHEGBOX for the interface to the parton shower programs PYTHIA or HERWIG. Phenomenological studies for the LHC and the Tevatron are presented with particular emphasis on the inclusion of spin-correlation effects in top decay and the impact of the parton shower on the top-quark charge asymmetries. As a novel application of the present calculation the measurement of the top-quark mass is discussed.
    06/2012;
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    S. Moch, P. Uwer, A. Vogt
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    ABSTRACT: 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 k_t-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.
    Physics Letters B 03/2012; 714(1). · 4.57 Impact Factor
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    ABSTRACT: We present a numerical implementation for virtual corrections to multi-jet production at Next-to-Leading order. Using the algorithm of generalised unitarity we compute primitive amplitudes from tree-level input. These basic ingredients are then used to compute full colour and helicity summed corrections.
    01/2012;
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    ABSTRACT: We present the publicly available program NGluon allowing the numerical evaluation of primitive amplitudes at one-loop order in massless QCD. The program allows the computation of one-loop amplitudes for an arbitrary number of gluons. The focus of the present article is the extension to one-loop amplitudes including an arbitrary number of massless quark pairs. We discuss in detail the algorithmic differences to the pure gluonic case and present cross checks to validate our implementation. The numerical accuracy is investigated in detail.
    Journal of Physics Conference Series 12/2011; 368(1).
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    ABSTRACT: We present a calculation of heavy-flavor production in hadronic collisions in association with one jet matched to parton shower Monte Carlo programs at next-to-leading order in perturbative QCD. Top-quark decays are included and spin correlations in the decay products are taken into account. The calculation builds on existing results for the radiative corrections to heavy-quark plus one jet production and uses the POWHEG BOX for the interface to the parton shower programs PYTHIA or HERWIG. A broad phenomenological study for the Large Hadron Collider and the Tevatron is presented. In particular we study---as one important sample application---the impact of the parton shower on the top-quark charge asymmetry.
    Journal of High Energy Physics 10/2011; · 5.62 Impact Factor
  • 01/2011;
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    ABSTRACT: 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.
    Computer Physics Communications 11/2010; 182(8). · 2.41 Impact Factor
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    ABSTRACT: 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.
    Computer Physics Communications 07/2010; 182(4). · 2.41 Impact Factor
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    ABSTRACT: Internal report | Preprint
    Red Report (2010),. 06/2010;

Publication Stats

2k Citations
161.25 Total Impact Points

Institutions

  • 2009–2013
    • Humboldt-Universität zu Berlin
      • Department of Physics
      Berlín, Berlin, Germany
  • 2001–2009
    • Karlsruhe Institute of Technology
      • Institute of Theoretical Particle Physics
      Karlsruhe, Baden-Wuerttemberg, Germany
  • 2008
    • Johannes Gutenberg-Universität Mainz
      • Institute of Physics
      Mayence, Rheinland-Pfalz, Germany
  • 2007–2008
    • Max Planck Institute of Physics
      München, Bavaria, Germany
  • 2004–2007
    • CERN
      • Physics Department (PH)
      Genève, Geneva, Switzerland
  • 1996
    • RWTH Aachen University
      • Institut für Theorie der statistischen Physik A
      Aachen, North Rhine-Westphalia, Germany