ALPGEN , a generator for hard multiparton processes in hadronic collisions 1

This paper presents a new event generator, ALPGEN, dedicated to the study of multiparton hard processes in hadronic collisions. The code performs, at the leading order in QCD and EW interactions, the calculation of the exact matrix elements for a large set of parton-level processes of interest in the study of the Tevatron and LHC data. The current version of the code describes the following final states: (W → lν)QQ+N jets and (Z/γ → ll̄)QQ+N jets (Q being a heavy quark), with N ≤ 4; (W → lν)+N jets and (Z/γ → ll̄) +N jets (N ≤ 6); nW +mZ + lH +N jets, with n+m+ l +N ≤ 8 and N ≤ 3; QQ+N jets (N ≤ 6); QQQ′Q′ +N jets, with Q and Q heavy quarks (possibly equal) and N ≤ 4; HQQ + N jets (N ≤ 4). Parton-level events are generated, providing full information on their colour and flavour structure, enabling the evolution of the partons into fully hadronised final states. CERN-TH/2002-129 April 27, 2002 The work of MLM and FP is supported in part by the EU Fourth Framework Programme “Training and Mobility of Researchers”, Network “Quantum Chromodynamics and the Deep Structure of Elementary Particles”, contract FMRX–CT98–0194 (DG 12 – MIHT). MM and RP acknowledge the finantial support of the European Union under contract HPRN-CT-2000-00149. ADP is supported by a M.Curie fellowship, contract HPMF-CT-2001-01178. On leave of absence from INFN Sezione di Pavia, Italy.