M. Worek

RWTH Aachen University, Aachen, North Rhine-Westphalia, Germany

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Publications (57)104.28 Total impact

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    G. Bevilacqua, M. Worek
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    ABSTRACT: Triggered by ongoing experimental analyses, we report on a study of the cross section ratio sigma(pp -> ttbb)/sigma(pp -> ttjj) at the next-to-leading order in QCD, focusing on both present and future collider energies: sqrt{s}= 7, 8, 13 TeV. In particular, we provide a comparison between our predictions and the currently available CMS data for the 8 TeV run. We further analyse the kinematics and scale uncertainties of the two processes for a single set of parton distribution functions, with the goal of assessing possible correlations that might help to reduce the theoretical error of the ratio and thus enhance the predictive power of this observable. We argue that the different jet kinematics makes the ttbb and ttjj processes uncorrelated in several observables, and show that the scale uncertainty is not significantly reduced when taking the ratio of the cross sections.
    Journal of High Energy Physics 03/2014; 2014(7). · 5.62 Impact Factor
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    Malgorzata Worek
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    ABSTRACT: The calculation of NLO QCD corrections to the production cross section of two bottom pairs at the LHC is briefly summarized. We describe the pp -> b anti-b b anti-b+X process both in the 4-flavor and 5-flavor scheme and investigate the effect of the finite bottom quark mass. The results for the total cross section and a few differential distributions are presented. They have been obtained with the Nagy-Soper subtraction formalism for real radiation at NLO. A comparison with results based on the traditional Catani-Seymour subtraction is also included.
    11/2013;
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    ABSTRACT: We extend the Helac-Dipoles package with the implementation of a new subtraction formalism, first introduced by Nagy and Soper in the formulation of an improved parton shower. We discuss a systematic, semi-numerical approach for the evaluation of the integrated subtraction terms for both massless and massive partons, which provides the missing ingredient for a complete implementation. In consequence, the new scheme can now be used as part of a complete NLO QCD calculation for processes with arbitrary parton masses and multiplicities. We assess its overall performance through a detailed comparison with results based on Catani-Seymour subtraction. The importance of random polarization and color sampling of the external partons is also examined.
    Journal of High Energy Physics 08/2013; 2013(10). · 5.62 Impact Factor
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    ABSTRACT: The production of four bottom quarks is an important benchmark channel for Higgs analyses and searches for new physics at the LHC. We report on the calculation of the next-to-leading order QCD corrections to the process $ pp\ \to\ b\overline{b}b\overline{b}+X $ with the Helac-NLO automated framework, and present results for inclusive cross sections and differential distributions. We discuss the impact of the higher-order corrections and, in particular, the effect of the bottom quark mass. In addition, we provide an estimate of the theoretical uncertainty from the variation of the renormalisation and factorisation scales and the parton distribution functions. The results are obtained with a new subtraction formalism for real radiation at next-to-leading order, implemented in the Helac-Dipoles package.
    Journal of High Energy Physics 07/2013; 2013(7). · 5.62 Impact Factor
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    ABSTRACT: The production of four bottom quarks is an important benchmark channel for Higgs analyses and searches for new physics at the LHC. We report on the calculation of the next-to-leading order QCD corrections to the process pp -> b anti-b b anti-b + X with the HELAC-NLO automated framework, and present results for inclusive cross sections and differential distributions. We discuss the impact of the higher-order corrections and, in particular, the effect of the bottom quark mass. In addition, we provide an estimate of the theoretical uncertainty from the variation of the renormalisation and factorisation scales and the parton distribution functions. The results are obtained with a new subtraction formalism for real radiation at next-to-leading order, implemented in the HELAC-DIPOLES package.
    04/2013;
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    Malgorzata Worek
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    ABSTRACT: A brief summary of the current status of the next-to-leading order QCD corrections to top quark pair production and the associated production of top anti-top with jet(s) in different configurations, i.e. with one jet, two jets and another top anti-top pair, is presented.
    Journal of Physics Conference Series 02/2013; 452(1).
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    G. Bevilacqua, M. Worek
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    ABSTRACT: Many theories, from Supersymmetry to models of Strong Electroweak Symmetry Breaking, look at the production of four top quarks as an interesting channel to evidentiate signals of new physics beyond the Standard Model. The production of four-top final states requires large partonic energies, above the 4mt threshold, that are available at the CERN Large Hadron Collider and will become more and more accessible with increasing energy and luminosity of the proton beams. A good theoretical control on the Standard Model background is a fundamental prerequisite for a correct interpretation of the possible signals of new physics that may arise in this channel. In this paper we report on the calculation of the next-to-leading order QCD corrections to the Standard Model process pp -> tttt + X. As it is customary for such studies, we present results for both integrated and differential cross sections. A judicious choice of a dynamical scale allows us to obtain nearly constant K-factors in most distributions.
    Journal of High Energy Physics 06/2012; 2012(7). · 5.62 Impact Factor
  • Malgorzata Worek
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    ABSTRACT: Motivated by ongoing experimental analyses, we report on the calculation of next-to-leading order QCD corrections to the production of $ t\overline t $ pairs in association with two hard b-jets at the Fermilab TeVatron. Besides the total cross section and its scale dependence, a few differential distributions applicable for Higgs boson searches at the TeVaron are given. The QCD corrections with respect to leading order are negative and small. For our main setup they amount to 2%, and remain reasonably stable against changes of cuts. This proves that an integrated next-to-leading order $ \mathcal{K} $ -factor does not necessarily need to be applied in the background estimation for the $ t\overline t H \to t\overline t b\overline b $ signal process. The distributions show similarly small corrections. The shape of kinematic distributions is distorted at most by about 20% in some corners of the phase space. Even though it is not the main purpose of this paper, we also evaluated the forward-backward asymmetry of the top quark at next-to-leading order.
    Journal of High Energy Physics 02/2012; 2012(2). · 5.62 Impact Factor
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    ABSTRACT: A comparison of theoretical results on NNLO leptonic and hadronic corrections to Bhabha scattering with the Monte Carlo generator BabaYaga@NLO used at meson factories is given. Complete NLO virtual corrections to the $e^+e^- \to \mu^+ \mu^- \gamma$ process are discussed.
    01/2012;
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    Malgorzata Worek
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    ABSTRACT: Motivated by ongoing experimental analyses, we report on the calculation of next-to-leading order QCD corrections to the production of top anti-top pairs in association with two hard b-jets at the Fermilab TeVatron. Besides the total cross section and its scale dependence, a few differential distributions applicable for Higgs boson searches at the TeVaron are given. The QCD corrections with respect to leading order are negative and small. For our main setup they amount to 2%, and remain reasonably stable against changes of cuts. This proves that an integrated next-to-leading order K-factor does not necessarily need to be applied in the background estimation for the top anti-top H -> top anti-top bottom anti-bottom signal process. The distributions show similarly small corrections. The shape of kinematic distributions is distorted at most by about 20% in some corners of the phase space. Even though it is not the main purpose of this paper, we also evaluated the forward-backward asymmetry of the top quark at next-to-leading order.
    12/2011;
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    ABSTRACT: We provide an exact calculation of next-to-next-to-leading order (NNLO) massive corrections to Bhabha scattering in QED, relevant for precision luminosity monitoring at meson factories. Using realistic reference event selections, exact numerical results for leptonic and hadronic corrections are given and compared with the corresponding approximate predictions of the event generator BabaYaga@NLO. It is shown that the NNLO massive corrections are necessary for luminosity measurements with per mille precision. At the same time they are found to be well accounted for in the generator at an accuracy level below the one per mille. An update of the total theoretical precision of BabaYaga@NLO is presented and possible directions for a further error reduction are sketched.
    Nuclear Physics B - Proceedings Supplements 12/2011; s 225–227. · 0.88 Impact Factor
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    Malgorzata Worek
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    ABSTRACT: The calculation of NLO QCD corrections to the $t\bar{t}\to W^{+}W^{-}b\bar{b}\to e^{+}\nu_e \mu^{-}\bar{\nu}_{\mu}b\bar{b}$ process with complete off-shell effects, is briefly summarized. Besides the total cross section and its scale dependence, a few differential distributions at the TeVatron run II and LHC are given. All results presented in this contribution have been obtained with the help of the HELAC-NLO Monte Carlo framework.
    10/2011;
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    Article: Helac-nlo
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    ABSTRACT: Based on the OPP technique and the HELAC framework, HELAC-1LOOP is a program that is capable of numerically evaluating QCD virtual corrections to scattering amplitudes. A detailed presentation of the algorithm is given, along with instructions to run the code and benchmark results. The program is part of the HELAC-NLO framework that allows for a complete evaluation of QCD NLO corrections.
    10/2011;
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    ABSTRACT: We report on the calculation of the next-to-leading order QCD corrections to the production of ttbar pairs in association with two hard jets at the Fermilab TeVatron and CERN Large Hadron Collider. Results for the integrated and differential cross sections are given. The corrections with respect to leading order are negative and moderate. A study of the scale dependence of our NLO predictions indicates that the residual theoretical uncertainty, due to higher order corrections, is 21% for the TeVatron and 15% for the LHC. In case of the TeVatron, the forward-backward asymmetry of the top quark is calculated for the first time at next-to-leading order. With the inclusive selection of cuts, this asymmetry amounts to A_FB = -10.3% at leading order and A_FB = -4.6% at next-to-leading order. All results presented in this paper have been obtained with the help of the HELAC-NLO package.
    Physical review D: Particles and fields 08/2011; 84(11).
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    ABSTRACT: Vbfnlo is a flexible parton level Monte Carlo program for the simulation of vector boson fusion (VBF), double and triple vector boson production (plus jet) in hadronic collisions at next-to-leading order (NLO) in the strong coupling constant, as well as Higgs boson plus two jet production via gluon fusion at the one-loop level. In the new release -- Version 2.6.0 -- several new processes have been added at NLO QCD: diboson production W\gamma, WZ, ZZ, Z\gamma and \gamma\gamma), same-sign W pair production via vector boson fusion and the triboson plus jet process W\gamma\gamma j. In addition, gluon induced diboson production has been implemented at the leading order (one-loop) level. The diboson processes WW, WZ and W\gamma can be run with anomalous gauge boson couplings, and anomalous couplings between a Higgs and a pair of gauge bosons is included in WW, ZZ, Z\gamma and \gamma\gamma diboson production. The code has also been extended to include anomalous couplings for single vector boson production via VBF, and a spin-2 model has been implemented for diboson pair production via vector boson fusion.
    07/2011;
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    ABSTRACT: Virtual fermionic N_f = 1 and N_f = 2 contributions to Bhabha scattering are combined with realistic real corrections at next-to-next-to-leading order in QED. The virtual corrections are determined by the package bha_nnlo_hf, and real corrections with the Monte Carlo generators Bhagen-1Ph, Helac-Phegas and Ekhara. Numerical results are discussed at the energies of and with realistic cuts used at the Phi factory DAFNE, at the B factories PEP-II and KEK, and at the charm/tau factory BEPC II. We compare these complete calculations with the approximate ones realized in the generator BabaYaga@NLO used at meson factories to evaluate their luminosities. For realistic reference event selections we find agreement for the NNLO leptonic and hadronic corrections within 0.07% or better and conclude that they are well accounted for in the generator by comparison with the present experimental accuracy.
    Journal of High Energy Physics 06/2011; 2011(7). · 5.62 Impact Factor
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    Malgorzata Worek
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    ABSTRACT: A very brief status of next-to-leading order QCD calculations is given. As an example the next-to-leading order QCD calculations to the pp -> ttjj processes at the CERN Large Hardon Collider are presented. Results for integrated and differential cross sections are shown. They have been obtained in the framework of the HELAC-NLO system. Comment: 6 pages, 4 figures. Presented at the XL International Symposium on Multiparticle Dynamics, ISMD 2010, 21-25 September 2010, Antwerp, Belgium
    12/2010;
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    ABSTRACT: Achieving a precise description of multi-parton final states is crucial for many analyses at LHC. In this contribution we review the main features of the HELAC-NLO system for NLO QCD calculations. As a case study, NLO QCD corrections for tt + 2 jet production at LHC are illustrated and discussed. Comment: 7 pages, 4 figures. Presented at 10th DESY Workshop on Elementary Particle Theory: Loops and Legs in Quantum Field Theory, Worlitz, Germany, April 25-30, 2010
    Nuclear Physics B - Proceedings Supplements 07/2010; · 0.88 Impact Factor
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    Malgorzata Worek
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    ABSTRACT: A report on the recent next-to-leading order QCD calculations to ttbb and ttjj at the CERN Large Hardon Collider is given. The elements of the calculation are briefly summarized and results for integrated and differential cross sections are presented.
    07/2010;
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    Malgorzata Worek
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    ABSTRACT: A report on the recent next-to-leading order QCD calculations to t anti-t b anti-b and t anti-t + 2j processes at the CERN Large Hardon Collider is presented. Results for integrated and differential cross sections are given. A significant reduction of the scale dependence is observed in both cases, which indicates that the perturbative expansion is well under control. The results are obtained in the framework of the HELAC-NLO system.
    05/2010;

Publication Stats

1k Citations
104.28 Total Impact Points

Institutions

  • 2013
    • RWTH Aachen University
      • Institut für Theoretische Teilchenphysik und Kosmologie (Theorie E)
      Aachen, North Rhine-Westphalia, Germany
  • 2010–2012
    • Bergische Universität Wuppertal
      • Physical and Theoretical Chemistry
      Wuppertal, North Rhine-Westphalia, Germany
  • 2002–2009
    • University of Silesia in Katowice
      • Institute of Physics
      Catowice, Silesian Voivodeship, Poland
  • 2008
    • Karlsruhe Institute of Technology
      • Institute of Theoretical Physics
      Karlsruhe, Baden-Wuerttemberg, Germany
  • 2006
    • Polish Academy of Sciences
      • Institute of Nuclear Physics
      Warsaw, Masovian Voivodeship, Poland
    • Institute of Nuclear Physics
      Cracovia, Lesser Poland Voivodeship, Poland
  • 2002–2003
    • CERN
      Genève, Geneva, Switzerland