Publications (43) View all
-
Article: Higher-Order Corrections to Timelike Jets
[show abstract] [hide abstract]
ABSTRACT: We present a simple formalism for the evolution of timelike jets in which tree-level matrix element corrections can be systematically incorporated, up to arbitrary parton multiplicities and over all of phase space, in a way that exponentiates the matching corrections. The scheme is cast as a shower Markov chain which generates one single unweighted event sample, that can be passed to standard hadronization models. Remaining perturbative uncertainties are estimated by providing several alternative weight sets for the same events, at a relatively modest additional overhead. As an explicit example, we consider Z -> q qbar evolution with unpolarized, massless quarks and include several formally subleading improvements as well as matching to tree-level matrix elements through alpha_s^4. The resulting algorithm is implemented in the publicly available VINCIA plugin to the PYTHIA 8 event generator.02/2011; -
Article: One-loop amplitudes for W+3 jet production in hadron collisions
[show abstract] [hide abstract]
ABSTRACT: We employ the recently developed method of generalized $D$-dimensional unitarity to compute one-loop virtual corrections to all scattering amplitudes relevant for the production of a $W$ boson in association with three jets in hadronic collisions, treating all quarks as massless.11/2008; -
Article: A simple shower and matching algorithm
[show abstract] [hide abstract]
ABSTRACT: We present a simple formalism for parton-shower Markov chains. As a first step towards more complete “uncertainty bands,” we incorporate a comprehensive exploration of the ambiguities inherent in such calculations. To reduce this uncertainty, we then introduce a matching formalism which allows a generated event sample to simultaneously reproduce any infrared-safe distribution calculated at leading or next-to-leading order in perturbation theory, up to subleading corrections. To enable a more universal definition of perturbative calculations, we also propose a more general definition of the hadronization cutoff. Finally, we present an implementation of some of these ideas for final-state gluon showers, in a code dubbed Vincia.Phys. Rev. D. 07/2008; 78(1). -
Article: Masses, fermions and generalized D-dimensional unitarity
[show abstract] [hide abstract]
ABSTRACT: We extend the generalized D-dimensional unitarity method for numerical evaluation of one-loop amplitudes by incorporating massive particles. The issues related to extending the spinor algebra to higher dimensions, treatment of external self-energy diagrams and mass renormalization are discussed within the context of the D-dimensional unitarity method. To validate our approach, we calculate in QCD the one-loop scattering amplitudes of a massive quark pair with up to three additional gluons for arbitrary spin states of the external quarks and gluons. Comment: 18 pages, 2 figures06/2008; -
Article: On the Numerical Evaluation of One-Loop Amplitudes: the Gluonic Case
[show abstract] [hide abstract]
ABSTRACT: We develop an algorithm of polynomial complexity for evaluating one-loop amplitudes with an arbitrary number of external particles. The algorithm is implemented in the Rocket program. Starting from particle vertices given by Feynman rules, tree amplitudes are constructed using recursive relations. The tree amplitudes are then used to build one-loop amplitudes using an integer dimension on-shell cut method. As a first application we considered only three and four gluon vertices calculating the pure gluonic one-loop amplitudes for arbitrary external helicity or polarization states. We compare our numerical results to analytical results in the literature, analyze the time behavior of the algorithm and the accuracy of the results, and give explicit results for fixed phase space points for up to twenty external gluons. Comment: 22 pages, 9 figures; v2: references added, version accepted for publication05/2008;
