P. Uwer

Humboldt-Universität zu Berlin, Berlín, Berlin, Germany

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Publications (104)214.06 Total impact

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    Till Martini · Peter Uwer
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    ABSTRACT: The Matrix Element Method (MEM) has proven beneficial to make maximal use of the information available in experimental data. However, so far it has mostly been used in Born approximation only. In this paper we discuss an extension to NLO accuracy. As a prerequisite we present an efficient method to calculate event weights for jet events at NLO accuracy. As illustration and proof of concept we apply the method to the extraction of the top-quark mass in e+e- annihilation. We observe significant differences when moving from LO to NLO which may be relevant for the interpretation of top-quark mass measurements at hadron colliders relying on the MEM.
    Preview · Article · Nov 2015 · Acta Physica Polonica Series B
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    ABSTRACT: We investigate the production of heavy, neutral Higgs boson resonances and their decays to top-quark top-antiquark ($t\bar{t}$) 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 $m_t$ limit with an effective K-factor rescaling. The non-resonant $t\bar{t}$ 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 $t\bar{t}$ threshold and unsuppressed Yukawa couplings to top quarks. For these three scenarios we compute, for the LHC operating at 13 TeV, the $t\bar{t}$ cross section and the distributions of the $t\bar{t}$ 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 $M_{t\bar{t}}$ bins we estimate the significances for detecting a heavy Higgs signal in the $t\bar{t}$ dileptonic and lepton plus jets decay channels.
    Preview · Article · Nov 2015
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    Till Martini · Peter Uwer
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    ABSTRACT: In this article we illustrate how event weights for jet events can be calculated efficiently at next-to-leading order (NLO) accuracy in QCD. This is a crucial prerequisite for the application of the Matrix Element Method in NLO. We modify the recombination procedure used in jet algorithms, to allow a factorisation of the phase space for the real corrections into resolved and unresolved regions. Using an appropriate infrared regulator the latter can be integrated numerically. As illustration, we reproduce differential distributions at NLO for two sample processes. As further application and proof of concept, we apply the Matrix Element Method in NLO accuracy to the mass determination of top quarks produced in e +e − annihilation. This analysis is relevant for a future Linear Collider. We observe a significant shift in the extracted mass depending on whether the Matrix Element Method is used in leading or next-to-leading order.
    Preview · Article · Jun 2015 · Journal of High Energy Physics
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    ABSTRACT: The top quark is the heaviest of all known elementary particles. It was discovered in 1995 by the CDF and DØ experiments at the Tevatron. With the start of the LHC in 2009, an unprecedented wealth of measurements of the top-quark’s production mechanisms and properties have been performed by the ATLAS and CMS collaborations, most of these resulting in smaller uncertainties than those achieved previously. At the same time, huge progress was made on the theoretical side yielding significantly improved predictions up to next-to-next-to-leading order in perturbative QCD. Due to the vast amount of events containing top quarks, a variety of new measurements became feasible and opened a new window to precisions tests of the Standard Model and to new-physics contributions.
    No preview · Article · Jun 2015
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    ABSTRACT: A comprehensive review of physics at an e+e- Linear Collider in the energy range of sqrt{s}=92 GeV--3 TeV is presented in view of recent and expected LHC results, experiments from low energy as well as astroparticle physics.The report focuses in particular on Higgs boson, Top quark and electroweak precision physics, but also discusses several models of beyond the Standard Model physics such as Supersymmetry, little Higgs models and extra gauge bosons. The connection to cosmology has been analyzed as well.
    Full-text · Article · Apr 2015 · European Physical Journal C
  • Werner Bernreuther · Peter Uwer
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    ABSTRACT: Results are reviewed which were obtained within the project Top-quark physics at colliders. These include QCD and weak-interaction corrections to hadronic production, determinations of the the top-quark mass, predictions of the charge asymmetry and spin correlations, NLO QCD corrections to hadronic -jet production, and partial results for hadronic t-channel single-top production at NNLO QCD. In addition, some methodical developments made in this project are outlined, which are relevant for NLO and NNLO QCD calculations.
    No preview · Article · Apr 2015
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    M. Assadsolimani · P. Kant · B. Tausk · P. Uwer
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    ABSTRACT: In this article we discuss the calculation of single top-quark production in the t-channel at two-loop order in QCD. In particular we present the decomposition of the amplitude according to its spin and colour structure and present complete results for the two-loop amplitudes in terms of master integrals. For the vertex corrections compact analytic expressions are given. The box contributions are implemented in a publicly available C program.
    Full-text · Article · Sep 2014 · Physical Review D
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    ABSTRACT: 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. For future applications we present in addition all scale dependent terms at NNLO accuracy. 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 briefly describe how to use the program and provide all required tools to repeat the aforementioned analysis.
    Full-text · Article · Jun 2014 · Computer Physics Communications
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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.
    Full-text · Article · May 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.
    Preview · Article · Dec 2013 · Journal of Physics Conference Series
  • P. Uwer
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    ABSTRACT: In this talk I discuss the importance of precise top-quark mass determinations. Some conceptual aspects of top-quark mass measurements as well as methods used/proposed in the past are presented. In addition an entirely new method, which has been proposed very recently by S. Alioli et al., is reviewed.
    No preview · Article · Nov 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.
    No preview · Article · Nov 2013 · The European Physical Journal Conferences
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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.
    Preview · Article · Sep 2013 · Physical Review D
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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.
    Full-text · Article · Aug 2013 · Computer Physics Communications
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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.
    No preview · Article · Jul 2013 · Journal of Physics Conference Series
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    J. H. Kühn · A. Scharf · P. Uwer
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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.
    Full-text · Article · May 2013 · Physical Review D
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    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 \ttbaronejet cross section with respect to its invariant mass $\sqrt{\sttj}$. 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.
    Full-text · Article · Mar 2013 · European Journal of Physics
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    ABSTRACT: The $t\bar{t}+\mbox{1-jet} + X$ differential cross-section in proton–proton collisions at 7 TeV centre of mass energy is investigated with respect to its sensitivity to the top quark mass. The analysis includes higher order QCD corrections at NLO. The impact of the renormalization scale (μ R), the factorization (μ F) scale and of the choice of different proton’s PDF (parton distribution function) has been evaluated. In this study it is concluded that differential jet rates offer a promising option for alternative mass measurements of the top quark, with theoretical uncertainties below 1 GeV.
    No preview · Article · Oct 2012 · Pramana
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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.
    Preview · Article · Sep 2012 · Computer Physics Communications
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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.
    Preview · Article · Sep 2012 · Physics Letters B

Publication Stats

3k Citations
214.06 Total Impact Points

Institutions

  • 2009-2015
    • Humboldt-Universität zu Berlin
      • Department of Physics
      Berlín, Berlin, Germany
  • 2008
    • Karlsruhe Institute of Technology
      Carlsruhe, Baden-Württemberg, Germany
  • 2004-2007
    • CERN
      • Physics Department (PH)
      Genève, Geneva, Switzerland
    • Durham University
      • Institute for Particle Physics Phenomenology "IPPP"
      Durham, England, United Kingdom
  • 1996
    • RWTH Aachen University
      • Institut für Theorie der statistischen Physik A
      Aachen, North Rhine-Westphalia, Germany