Top-pair production and decay at NLO matched with parton showers

  • John M. Campbell
  • R. Keith Ellis
  • Paolo Nason
  • Emanuele Re
Open Access
Regular Article - Theoretical Physics

Abstract

We present a next-to-leading order (NLO) calculation of \( t\overline{t} \) production in hadronic collisions interfaced to shower generators according to the POWHEG method. We start from an NLO result from previous work, obtained in the zero width limit, where radiative corrections to both production and decays are included. The POWHEG interface required an extension of the POWHEG BOX framework, in order to deal with radiation from the decay of resonances. This extension is fully general (i.e. it can be applied in principle to any process considered in the zero width limit), and is here applied for the first time. In order to perform a realistic simulation, we introduce finite width effects using different approximations, that we validated by comparing with published exact NLO results. We have interfaced our POWHEG code to the PYTHIA8 shower Monte Carlo generator. At this stage, we dealt with novel issues related to the treatment of resonances, especially with regard to the initial scale for the shower that needs to be set appropriately. This procedure affects, for example, the fragmentation function of the b quark, that we have studied with particular attention. We believe that the tool presented here improves over previous generators for all aspects that have to do with top decays, and especially for the study of issues related to top mass measurements that involve B hadrons or b jets. The work presented here also constitutes a first step towards a fully consistent matching of NLO calculations involving intermediate resonances decaying into coloured particles, with parton showers.

Keywords

Monte Carlo Simulations NLO Computations 

Notes

Open Access

This article is distributed under the terms of the Creative Commons Attribution License (CC-BY 4.0), which permits any use, distribution and reproduction in any medium, provided the original author(s) and source are credited.

References

  1. [1]
    CMS collaboration, Measurement of the \( t\overline{t} \) production cross section in the all-jet final state in pp collisions at \( \sqrt{s}=7 \) TeV, JHEP 05 (2013) 065 [arXiv:1302.0508] [INSPIRE].ADSGoogle Scholar
  2. [2]
    CMS collaboration, Measurement of the \( t\overline{t} \) production cross section in pp collisions at \( \sqrt{s}=7 \) TeV with lepton + jets final states, Phys. Lett. B 720 (2013) 83 [arXiv:1212.6682] [INSPIRE].ADSGoogle Scholar
  3. [3]
    CMS collaboration, Measurement of the \( t\overline{t} \) production cross section in the dilepton channel in pp collisions at \( \sqrt{s}=8 \) TeV, JHEP 02 (2014) 024 [Erratum ibid. 1402 (2014) 102] [arXiv:1312.7582] [INSPIRE].
  4. [4]
    ATLAS collaboration, Measurement of the \( t\overline{t} \) production cross-section as a function of jet multiplicity and jet transverse momentum in 7 TeV proton-proton collisions with the ATLAS detector, JHEP 01 (2015) 020 [arXiv:1407.0891] [INSPIRE].ADSGoogle Scholar
  5. [5]
    ATLAS collaboration, Measurement of the \( t\overline{t} \) production cross-section using eμ events with b-tagged jets in pp collisions at \( \sqrt{s}=7 \) and 8 TeV with the ATLAS detector, Eur. Phys. J. C 74 (2014) 3109 [arXiv:1406.5375] [INSPIRE].ADSGoogle Scholar
  6. [6]
    ATLAS collaboration, Measurement of the ttbar production cross section in the tau+jets channel using the ATLAS detector, Eur. Phys. J. C 73 (2013) 2328 [arXiv:1211.7205] [INSPIRE].ADSGoogle Scholar
  7. [7]
    CMS collaboration, Measurement of the top-quark mass in all-jets \( t\overline{t} \) events in pp collisions at \( \sqrt{s}=7 \) TeV, Eur. Phys. J. C 74 (2014) 2758 [arXiv:1307.4617] [INSPIRE].ADSGoogle Scholar
  8. [8]
    CMS collaboration, Determination of the top-quark pole mass and strong coupling constant from the t t-bar production cross section in pp collisions at \( \sqrt{s}=7 \) TeV, Phys. Lett. B 728 (2014) 496 [Erratum ibid. B 728 (2014) 526] [arXiv:1307.1907] [INSPIRE].
  9. [9]
    CMS collaboration, Measurement of masses in the \( t\overline{t} \) system by kinematic endpoints in pp collisions at \( \sqrt{s}=7 \) TeV, Eur. Phys. J. C 73 (2013) 2494 [arXiv:1304.5783] [INSPIRE].ADSGoogle Scholar
  10. [10]
    CMS collaboration, Measurements of \( t\overline{t} \) spin correlations and top-quark polarization using dilepton final states in pp collisions at \( \sqrt{s}=7 \) TeV, Phys. Rev. Lett. 112 (2014) 182001 [arXiv:1311.3924] [INSPIRE].ADSCrossRefGoogle Scholar
  11. [11]
    CMS collaboration, Measurement of differential top-quark pair production cross sections in pp colisions at \( \sqrt{s}=7 \) TeV, Eur. Phys. J. C 73 (2013) 2339 [arXiv:1211.2220] [INSPIRE].ADSGoogle Scholar
  12. [12]
    ATLAS collaboration, Measurements of normalized differential cross sections for \( t\overline{t} \) production in pp collisions at \( \sqrt{s}=7 \) TeV using the ATLAS detector, Phys. Rev. D 90 (2014) 072004 [arXiv:1407.0371] [INSPIRE].ADSGoogle Scholar
  13. [13]
    ATLAS collaboration, Measurements of top quark pair relative differential cross-sections with ATLAS in pp collisions at \( \sqrt{s}=7 \) TeV, Eur. Phys. J. C 73 (2013) 2261 [arXiv:1207.5644] [INSPIRE].ADSGoogle Scholar
  14. [14]
    M. Czakon, P. Fiedler and A. Mitov, Total Top-Quark Pair-Production Cross Section at Hadron Colliders Through O(α S4), Phys. Rev. Lett. 110 (2013) 252004 [arXiv:1303.6254] [INSPIRE].ADSCrossRefGoogle Scholar
  15. [15]
    G. Abelof, A. Gehrmann-De Ridder, P. Maierhofer and S. Pozzorini, NNLO QCD subtraction for top-antitop production in the \( q\overline{q} \) channel, JHEP 08 (2014) 035 [arXiv:1404.6493] [INSPIRE].ADSCrossRefGoogle Scholar
  16. [16]
    M. Czakon, P. Fiedler and A. Mitov, Resolving the Tevatron top quark forward-backward asymmetry puzzle, arXiv:1411.3007 [INSPIRE].
  17. [17]
    M. Brucherseifer, F. Caola and K. Melnikov, \( \mathcal{O}\left({\alpha}_s^2\right) \) corrections to fully-differential top quark decays, JHEP 04 (2013) 059 [arXiv:1301.7133] [INSPIRE].ADSCrossRefGoogle Scholar
  18. [18]
    M.L. Mangano, P. Nason and G. Ridolfi, Heavy quark correlations in hadron collisions at next-to-leading order, Nucl. Phys. B 373 (1992) 295 [INSPIRE].ADSCrossRefGoogle Scholar
  19. [19]
    S. Frixione, P. Nason and B.R. Webber, Matching NLO QCD and parton showers in heavy flavor production, JHEP 08 (2003) 007 [hep-ph/0305252] [INSPIRE].ADSCrossRefGoogle Scholar
  20. [20]
    S. Frixione, P. Nason and G. Ridolfi, A Positive-weight next-to-leading-order Monte Carlo for heavy flavour hadroproduction, JHEP 09 (2007) 126 [arXiv:0707.3088] [INSPIRE].ADSCrossRefGoogle Scholar
  21. [21]
    S. Frixione, E. Laenen, P. Motylinski and B.R. Webber, Angular correlations of lepton pairs from vector boson and top quark decays in Monte Carlo simulations, JHEP 04 (2007) 081 [hep-ph/0702198] [INSPIRE].ADSCrossRefGoogle Scholar
  22. [22]
    W. Bernreuther, A. Brandenburg, Z.G. Si and P. Uwer, Top quark pair production and decay at hadron colliders, Nucl. Phys. B 690 (2004) 81 [hep-ph/0403035] [INSPIRE].ADSCrossRefGoogle Scholar
  23. [23]
    K. Melnikov and M. Schulze, NLO QCD corrections to top quark pair production and decay at hadron colliders, JHEP 08 (2009) 049 [arXiv:0907.3090] [INSPIRE].ADSCrossRefGoogle Scholar
  24. [24]
    J.M. Campbell and R.K. Ellis, Top-quark processes at NLO in production and decay, J. Phys. G 42 (2015) 015005 [arXiv:1204.1513] [INSPIRE].ADSCrossRefGoogle Scholar
  25. [25]
    A. Denner, S. Dittmaier, S. Kallweit and S. Pozzorini, NLO QCD corrections to WWbb production at hadron colliders, Phys. Rev. Lett. 106 (2011) 052001 [arXiv:1012.3975] [INSPIRE].ADSCrossRefGoogle Scholar
  26. [26]
    A. Denner, S. Dittmaier, S. Kallweit and S. Pozzorini, NLO QCD corrections to off-shell top-antitop production with leptonic decays at hadron colliders, JHEP 10 (2012) 110 [arXiv:1207.5018] [INSPIRE].ADSCrossRefGoogle Scholar
  27. [27]
    G. Bevilacqua, M. Czakon, A. van Hameren, C.G. Papadopoulos and M. Worek, Complete off-shell effects in top quark pair hadroproduction with leptonic decay at next-to-leading order, JHEP 02 (2011) 083 [arXiv:1012.4230] [INSPIRE].ADSCrossRefGoogle Scholar
  28. [28]
    G. Heinrich, A. Maier, R. Nisius, J. Schlenk and J. Winter, NLO QCD corrections to \( {W}^{+}{W}^{-}b\overline{b} \) production with leptonic decays in the light of top quark mass and asymmetry measurements, JHEP 06 (2014) 158 [arXiv:1312.6659] [INSPIRE].ADSCrossRefGoogle Scholar
  29. [29]
    R. Frederix, Top Quark Induced Backgrounds to Higgs Production in the W W (∗)llνν Decay Channel at Next-to-Leading-Order in QCD, Phys. Rev. Lett. 112 (2014) 082002 [arXiv:1311.4893] [INSPIRE].ADSCrossRefGoogle Scholar
  30. [30]
    F. Cascioli, S. Kallweit, P. Maierhöfer and S. Pozzorini, A unified NLO description of top-pair and associated Wt production, Eur. Phys. J. C 74 (2014) 2783 [arXiv:1312.0546] [INSPIRE].ADSCrossRefGoogle Scholar
  31. [31]
    M.V. Garzelli, A. Kardos and Z. Trócsanyi, Hadroproduction of \( {W}^{+}{W}^{-}b\overline{b} \) at NLO accuracy matched with shower Monte Carlo programs, JHEP 08 (2014) 069 [arXiv:1405.5859] [INSPIRE].ADSCrossRefGoogle Scholar
  32. [32]
    P. Nason, A New method for combining NLO QCD with shower Monte Carlo algorithms, JHEP 11 (2004) 040 [hep-ph/0409146] [INSPIRE].ADSCrossRefGoogle Scholar
  33. [33]
    S. Frixione and B.R. Webber, Matching NLO QCD computations and parton shower simulations, JHEP 06 (2002) 029 [hep-ph/0204244] [INSPIRE].ADSCrossRefGoogle Scholar
  34. [34]
    S. Badger, R. Sattler and V. Yundin, One-Loop Helicity Amplitudes for \( t\overline{t} \) Production at Hadron Colliders, Phys. Rev. D 83 (2011) 074020 [arXiv:1101.5947] [INSPIRE].ADSGoogle Scholar
  35. [35]
    S. Alioli, P. Nason, C. Oleari and E. Re, A general framework for implementing NLO calculations in shower Monte Carlo programs: the POWHEG BOX, JHEP 06 (2010) 043 [arXiv:1002.2581] [INSPIRE].ADSCrossRefMATHGoogle Scholar
  36. [36]
    J. Alwall, M. Herquet, F. Maltoni, O. Mattelaer and T. Stelzer, MadGraph 5: Going Beyond, JHEP 06 (2011) 128 [arXiv:1106.0522] [INSPIRE].ADSCrossRefMATHGoogle Scholar
  37. [37]
    E. Boos et al., Generic user process interface for event generators, hep-ph/0109068 [INSPIRE].
  38. [38]
    S. Alioli, P. Nason, C. Oleari and E. Re, Vector boson plus one jet production in POWHEG, JHEP 01 (2011) 095 [arXiv:1009.5594] [INSPIRE].ADSCrossRefMATHGoogle Scholar
  39. [39]
    A. Kardos, P. Nason and C. Oleari, Three-jet production in POWHEG, JHEP 04 (2014) 043 [arXiv:1402.4001] [INSPIRE].ADSCrossRefGoogle Scholar
  40. [40]
    A.D. Martin, W.J. Stirling, R.S. Thorne and G. Watt, Parton distributions for the LHC, Eur. Phys. J. C 63 (2009) 189 [arXiv:0901.0002] [INSPIRE].ADSCrossRefMATHGoogle Scholar
  41. [41]
    H.-L. Lai et al., New parton distributions for collider physics, Phys. Rev. D 82 (2010) 074024 [arXiv:1007.2241] [INSPIRE].ADSGoogle Scholar
  42. [42]
    R.D. Ball et al., A first unbiased global NLO determination of parton distributions and their uncertainties, Nucl. Phys. B 838 (2010) 136 [arXiv:1002.4407] [INSPIRE].ADSCrossRefMATHGoogle Scholar
  43. [43]
    M. Cacciari, G.P. Salam and G. Soyez, The Anti-k(t) jet clustering algorithm, JHEP 04 (2008) 063 [arXiv:0802.1189] [INSPIRE].ADSCrossRefMATHGoogle Scholar
  44. [44]
    M. Cacciari, G.P. Salam and G. Soyez, FastJet User Manual, Eur. Phys. J. C 72 (2012) 1896 [arXiv:1111.6097] [INSPIRE].ADSCrossRefGoogle Scholar
  45. [45]
    W. Bernreuther and Z.-G. Si, Top quark spin correlations and polarization at the LHC: standard model predictions and effects of anomalous top chromo moments, Phys. Lett. B 725 (2013) 115 [arXiv:1305.2066] [INSPIRE].ADSCrossRefGoogle Scholar

Copyright information

© The Author(s) 2015

Authors and Affiliations

  • John M. Campbell
    • 1
  • R. Keith Ellis
    • 1
  • Paolo Nason
    • 2
  • Emanuele Re
    • 3
  1. 1.FermilabBataviaUnited States
  2. 2.INFN, Sezione di Milano BicoccaMilanoItaly
  3. 3.Rudolf Peierls Centre for Theoretical PhysicsUniversity of OxfordOxfordUnited Kingdom

Personalised recommendations