M. Worek

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

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Publications (40)122.6 Total impact

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    ABSTRACT: We present an MC@NLO-like matching of next-to-leading order QCD calculations with the Nagy-Soper parton shower. An implementation of the algorithm within the HELAC-DIPOLES Monte Carlo generator is used to address the uncertainties and ambiguities of the matching scheme. First results obtained using the Nagy-Soper parton shower implementation in DEDUCTOR in conjunction with the HELAC-NLO framework are given for the pp -> top anti-top j + X process at the LHC with sqrt(s)=8 TeV. Effects of resummation are discussed for various observables.
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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). DOI:10.1007/JHEP07(2014)135 · 6.22 Impact Factor
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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). DOI:10.1007/JHEP10(2013)204 · 6.22 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). DOI:10.1007/JHEP07(2013)095 · 6.22 Impact Factor
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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). DOI:10.1007/JHEP07(2012)111 · 6.22 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.
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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. DOI:10.1016/j.nuclphysbps.2012.02.061 · 0.88 Impact Factor
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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.
    Computer Physics Communications 10/2011; 184(3). DOI:10.1016/j.cpc.2012.10.033 · 2.41 Impact Factor
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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). DOI:10.1103/PhysRevD.84.114017 · 4.86 Impact Factor
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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.
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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). DOI:10.1007/JHEP07(2011)126 · 6.22 Impact Factor
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    ABSTRACT: Results for next-to-leading order QCD corrections to the pp( p[`(p)] ) ® t[`(t)] ® W+ W- b[`(b)] ® e+ nem- [`(n)]m b[`(b)] + X pp\left( {p\bar{p}} \right) \to t\bar{t} \to {W^{+} }{W^{-} }b\bar{b} \to {e^{+} }{\nu_e}{\mu^{-} }{\bar{\nu }_\mu }b\bar{b} + X processes with complete off-shell effects are presented for the first time. Double-, single-and non-resonant top contributions of the order O( as3a4 ) \mathcal{O}\left( {\alpha_s^3{\alpha^4}} \right) are consistently taken into account, which requires the introduction of a complex-mass scheme for unstable top quarks. Moreover, the intermediate W bosons are treated off-shell. Comparison to the narrow width approximation for top quarks, where non-factorizable corrections are not accounted for is performed. Besides the total cross section and its scale dependence, several differential distributions at the TeVatron run II and the LHC are given. In case of the TeVatron the forward-backward asymmetry of the top is recalculated afresh. With inclusive selection cuts, the forward-backward asymmetry amounts to AFBt = 0.051±0.0013 A_{FB}^t = 0.051\pm 0.0013 . Furthermore, the corrections with respect to leading order are positive and of the order 2.3% for the TeVatron and 47% for the LHC. A study of the scale dependence of our NLO predictions indicates that the residual theoretical uncertainty due to higher order corrections is 8% for the TeVatron and 9% for the LHC. KeywordsJets–NLO Computations–Hadronic Colliders–QCD
    Journal of High Energy Physics 02/2011; 2011(2):1-30. DOI:10.1007/JHEP02(2011)083 · 6.22 Impact Factor
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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; 205-206. DOI:10.1016/j.nuclphysbps.2010.08.045 · 0.88 Impact Factor
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    ABSTRACT: We report the results of a next-to-leading order simulation of top quark pair production in association with two jets. With our inclusive cuts, we show that the corrections with respect to leading order are negative and small, reaching 11%. The error obtained by scale variation is of the same order. Additionally, we reproduce the result of a previous study of top quark pair production in association with a single jet.
    Physical Review Letters 04/2010; 104(16):162002. DOI:10.1103/PHYSREVLETT.104.162002 · 7.73 Impact Factor
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    ABSTRACT: This report summarizes the activities of the SM and NLO Multileg Working Group of the Workshop "Physics at TeV Colliders", Les Houches, France 8-26 June, 2009.
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    ABSTRACT: The VBFNLO program package is a collection of Monte Carlo programs for the calculation of NLO QCD corrections to vector boson fusion cross sections, double and triple vector boson production, or the production of two electroweak bosons in association with an additional jet. An overview is given of the processes and features implemented in VBFNLO. WWgamma and Wgamma jet production are discussed as examples.
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    ABSTRACT: Weak boson scattering processes provide particularly promising means for gaining insight into the mechanism of electroweak symmetry breaking at hadron colliders. Being very sensitive to interactions in the weak gauge boson sector, they will help to distinguish the Standard Model from various new physics scenarios such as extra-dimensional Higgsless models. To unambiguously identify signatures of new physics, precise predictions for experimentally accessible observables within realistic selection cuts are crucial, including next-to-leading order QCD corrections. Here, we review how flexible Monte-Carlo methods can be employed for precision analyses of weak boson scattering reactions within the Standard Model and beyond.
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    ABSTRACT: We present the achievements of the last years of the experimental and theoretical groups working on hadronic cross section measurements at the low energy e+e- colliders in Beijing, Frascati, Ithaca, Novosibirsk, Stanford and Tsukuba and on tau decays. We sketch the prospects in these fields for the years to come. We emphasise the status and the precision of the Monte Carlo generators used to analyse the hadronic cross section measurements obtained as well with energy scans as with radiative return, to determine luminosities and tau decays. The radiative corrections fully or approximately implemented in the various codes and the contribution of the vacuum polarisation are discussed. Comment: Report of the "Working Group on Radiative Corrections and Monte Carlo Generators for Low Energies"; 99 pages, submitted to EPJC
    European Physical Journal C 12/2009; DOI:10.1140/epjc/s10052-010-1251-4 · 5.44 Impact Factor
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    ABSTRACT: Vbfnlo is a fully flexible parton level Monte Carlo program for the simulation of vector boson fusion, double and triple vector boson production in hadronic collisions at next-to-leading order in the strong coupling constant. Vbfnlo includes Higgs and vector boson decays with full spin correlations and all off-shell effects. In addition, Vbfnlo implements -even and -odd Higgs boson via gluon fusion, associated with two jets, at the leading-order one-loop level with the full top- and bottom-quark mass dependence in a generic two-Higgs-doublet model.
    Computer Physics Communications 09/2009; 180(9-180):1661-1670. DOI:10.1016/j.cpc.2009.03.006 · 2.41 Impact Factor
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    ABSTRACT: We present the results of a next-to-leading order calculation of QCD corrections to the production of an on-shell top-anti-top quark pair in association with two flavored b-jets. Besides studying the total cross section and its scale dependence, we give several differential distributions. Where comparable, our results agree with a previous analysis. While the process under scrutiny is of major relevance for Higgs boson searches at the LHC, we use it to demonstrate the ability of our system built around Helac-Phegas to tackle complete calculations at the frontier of current studies for the LHC. On the technical side, we show how the virtual corrections are efficiently computed with Helac-1Loop, based on the OPP method and the reduction code CutTools, using reweighting and Monte Carlo over color configurations and polarizations. As far as the real corrections are concerned, we use the recently published Helac-Dipoles package. In connection with improvements of the latter, we give the last missing integrated dipole formulae necessary for a complete implementation of phase space restriction dependence in the massive dipole subtraction formalism.
    Journal of High Energy Physics 09/2009; 9(09). DOI:10.1088/1126-6708/2009/09/109 · 6.22 Impact Factor

Publication Stats

1k Citations
122.60 Total Impact Points

Institutions

  • 2013–2015
    • 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
  • 2008–2009
    • Silesian University of Technology
      • Institute of Physics
      Gleiwitz, Silesian Voivodeship, Poland
  • 2002–2009
    • University of Silesia in Katowice
      • Institute of Physics
      Catowice, Silesian Voivodeship, Poland
  • 2006
    • Polish Academy of Sciences
      • Institute of Nuclear Physics
      Warsaw, Masovian Voivodeship, Poland
    • National Center for Scientific Research Demokritos
      • Institute of Nuclear and Particle Physics
      Athínai, Attica, Greece
  • 2005–2006
    • Institute of Nuclear Physics
      Cracovia, Lesser Poland Voivodeship, Poland