A Positive-Weight Next-to-Leading-Order Monte Carlo for Z Pair Hadroproduction

We present a first application of a previously published method for the computation of QCD processes that is accurate at next-to-leading order, and that can be interfaced consistently to standard shower Monte Carlo programs. We have considered Z pair production in hadron-hadron collisions, a process whose complexity is sufficient to test the general applicability of the method. We have interfaced our result to the HERWIG and PYTHIA shower Monte Carlo programs. Previous work on next-to-leading order corrections in a shower Monte Carlo (the MC@NLO program) may involve the generation of events with negative weights, that are avoided with the present method. We have compared our results with those obtained with MC@NLO, and found remarkable consistency. Our method can also be used as a standalone, alternative implementation of QCD corrections, with the advantage of positivity, improved convergence, and next-to-leading logarithmic accuracy in the region of small transverse momentum of the radiated parton.

[1]  J. Kanzaki,et al.  Generic User Process Interface for Event Generators , 2001 .

[2]  G. Ridolfi,et al.  Problems in the resummation of soft-gluon effects in the transverse-momentum distributions of massive vector bosons in hadronic collisions , 1998, hep-ph/9809367.

[3]  P. Nason.  A new method for combining NLO QCD with shower Monte Carlo algorithms , 2004, hep-ph/0409146.

[4]  L. Lönnblad.  Ariadne version 4 — A program for simulation of QDC cascades implementing the colour dipole model , 1992 .

[5]  Z. Kunszt,et al.  Vector boson pair production in hadronic collisions at O ( α s ) : Lepton correlations and anomalous couplings , 1999, hep-ph/9907305.

[6]  S. Moretti,et al.  HERWIG 6: an event generator for hadron emission reactions with interfering gluons (including supersymmetric processes) , 2001 .

[7]  P. Nason,et al.  Matching NLO QCD and parton showers in heavy flavour production , 2003, hep-ph/0305252.

[8]  Y. Dokshitzer,et al.  Hard Processes in Quantum Chromodynamics , 1980 .

[9]  R. Ellis,et al.  An update on vector boson pair production at hadron colliders , 1999, hep-ph/9905386.

[10]  S. Kawabata,et al.  A new version of the multi-dimensional integration and event generation package BASES/SPRING , 1995 .

[11]  M. A. Dobbs,et al.  Les Houches guidebook to Monte Carlo generators for hadron collider physics - eScholarship , 2003 .

[12]  S. Mrenna,et al.  Pythia 6.3 physics and manual , 2003, hep-ph/0308153.

[13]  S. Frixione,et al.  Matching NLO QCD computations and parton shower simulations , 2002, hep-ph/0204244.

[14]  S. Frixione,et al.  The MC@NLO event generator , 2002, hep-ph/0207182.

[15]  Davison E. Soper,et al.  Matching parton showers to NLO computations , 2005 .

[16]  B. Webber,et al.  QCD coherent branching and semi-inclusive processes at large χ , 1991 .

[17]  L. Suter,et al.  Herwig++ 2.5 Release Note , 2002, 1102.1672.

[18]  G. Gustafson,et al.  Dipole formulation of QCD cascades , 1988 .

[19]  J. Huston,et al.  Parton distributions and the strong coupling: CTEQ6AB PDFs , 2005, hep-ph/0512167.

[20]  P. Motylinski,et al.  Preprint typeset in JHEP style.- PAPER VERSION Cavendish–HEP–05/24 , 2005 .

[21]  W and Z transverse momentum distributions: resummation in qT-space , 1997, hep-ph/9706526.

[22]  B. Mele,et al.  QCD radiative corrections to Z boson pair production in hadronic collisions , 1991 .