KaTie: For parton-level event generation with [formula omitted]-dependent initial states

Abstract

KaTie is a parton-level event generator for hadron scattering processes that can deal with partonic initial-state momenta with an explicit transverse momentum dependence causing them to be space-like. Provided with the necessary transverse momentum dependent parton density functions, it calculates the tree-level off-shell matrix elements and performs the phase space importance sampling to produce weighted events, for example in the Les Houches Event File format. It can deal with arbitrary processes within the Standard Model, for up to at least four final-state particles. Furthermore, it can produce events for single-parton scattering as well as for multi-parton scattering. Program summaryProgram Title:KaTieProgram Files doi:http://dx.doi.org/10.17632/yrtgg8w9k8.1Licensing provisions: GPLv3Programming language: Fortran 2003 (implemented at least as far as in for example gfortran-4.6), Python (2.x with x≥6 or 3.x), BashExternal routines/libraries: Requires avhlib [1] and LHAPDF-6.x [2]Nature of problem: Factorization prescriptions for the cross section calculation of hadron scattering processes that allow for non-vanishing transverse momentum components for the initial-state partons require matrix elements with off-shell initial-state partons. Furthermore, the calculation of such cross sections requires the integration over these initial-state degrees of freedom, besides the components along the colliding hadrons and the final-state phase space degrees of freedom.Solution method: The Monte Carlo method is applied to create event files with which distributions for arbitrary observables can be evaluated. Tree-level off-shell matrix elements are defined as proposed in [3] and evaluated using Dyson–Schwinger recursion [4]. The whole procedure is automated for any process within the Standard Model, including the full particle content with all mass and coupling dependencies except the CKM matrix, but including the Higgs–gluon and Higgs–photon effective interactions.Restrictions: The matrix elements are tree-level matrix elements, and the maximal number of final-state particles is 9. The maximal number (initial plus final) of color pairs (gluons and/or quark–antiquark-pairs) for reasonable execution time is 6. Processes are restricted to the Standard Model, including the Higgs–gluon and Higgs–photon effective interactions.[1] M. Bury and A. van Hameren, Numerical evaluation of multi-gluon amplitudes for High Energy Factorization, Comput. Phys. Commun196 (2015) 592. http://bitbucket.org/hameren/avhlib[2] A. Buckley, J. Ferrando, S. Lloyd, K. Nordström, B. Page, M. Rüfenacht, M. Schönherr and G. Watt, LHAPDF6: parton density access in the LHC precision era, Eur. Phys. J. C75 (2015) 132. http://lhapdf.hepforge.org/[3] A. van Hameren, P. Kotko, and K. Kutak, Helicity amplitudes for high-energy scattering, JHEP01 (2013) 078.[4] F. Caravaglios and M. Moretti, An algorithm to compute Born scattering amplitudes without Feynman graphs, Phys. Lett. B358 (1995) 332. A. Kanaki, C.G. Papadopoulos, HELAC: A Package to compute electroweak helicity amplitudes, Comput. Phys. Commun.132 (2000) 306.