8 Search Results

For more than a decade the current generation of CPU-based matrix element generators has provided hard scattering events with excellent flexibility and good efficiency.However, they are a bottleneck of current Monte Carlo event generator toolchains, and with the advent of the HL-LHC and more demanding precision requirements, faster matrix elements are needed, especially at intermediate to large jet multiplicities.We present first results of the new BlockGen family of matrix element algorithms, featuring GPU support and novel color treatments, and discuss the best choice to deliver the performance needed for the next generation of accelerated matrix element generators.

In this paper we use our previously developed projective phase space generator for the calculation of the hadronic production of a vector boson with one additional jet at Next-to-Leading Order. The projective phase space generator allows us to make physical predictions in novel ways, speeding up both evaluation time and attainable accuracy. For the numerical evaluation we explore a computational model which combines the use of both multi-threading and distributed resources through the use of grid or cloud computing without depending on local institutional computer availability. The projective phase space method is well suited for this approach and gives throughmore » the use of cloud computing instant access to a large pool of resources.« less

Here, we present the first complete calculation of Z-boson production in association with a jet in hadronic collisions through next-to-next-to-leading order in perturbative QCD. Our computation uses the recently proposed N-jettiness subtraction scheme to regulate the infrared divergences that appear in the real-emission contributions. We present phenomenological results for 13 TeV proton-proton collisions with fully realistic fiducial cuts on the final-state particles. The remaining theoretical uncertainties after the inclusion of our calculations are at the percent level, making the Z+jet channel ready for precision studies at the LHC run II.

We develop a forward branching phase-space generator for use in next-to-leading order parton level event generators. By performing 2 -> 3 branchings from a fixed jet phase-space point, all bremsstrahlung events contributing to the given jet configuration are generated. The resulting phase-space integration is three-dimensional irrespective of the considered jet multiplicity. In this first study, we use the forward branching phase-space generator to calculate in the leading-color approximation next-to-leading order corrections to fully differential gluonic jet configurations.

A leading-order, leading-color parton-level event generator is developed for use on a multi-threaded GPU. Speed-up factors between 150 and 300 are obtained compared to an unoptimized CPU-based implementation of the event generator. In this first paper we study the feasibility of a GPU-based event generator with an emphasis on the constraints imposed by the hardware. Some studies of Monte Carlo convergence and accuracy are presented for PP -> 2,...,10 jet observables using of the order of 1e11 events.

Conventional cone jet algorithms arose from heuristic considerations of LO hard scattering coupled to independent showering. These algorithms implicitly assume that the final states of individual events can be mapped onto a unique set of jets that are in turn associated with a unique set of underlying hard scattering partons. Thus each final state hadron is assigned to a unique underlying parton. The Jet Energy Flow (JEF) analysis described here does not make such assumptions. The final states of individual events are instead described in terms of flow distributions of hadronic energy. Quantities of physical interest are constructed from themore » energy flow distribution summed over all events. The resulting analysis is less sensitive to higher order perturbative corrections and the impact of showering and hadronization than the standard cone algorithms.« less

In this paper the evaluation of matrix elements for a vector boson decaying into n partons (n ≤ 6) is presented. For this purpose recursive techniques and Weyl-van der Waerden spinor calculus are used. By appropriately crossing partons the amplitudes can be used to describe the production of a W and jets. The four-jet case is of particular interest as background to interesting physics signals. Numerical results are given for present and future accelerator energies. Also the signal versus background question for top quark search is briefly discussed.