A framework to include triple collinear splitting functions into parton showers is presented, and the implementation of flavor-changing next-to-leading-order (NLO) splitting kernels is discussed as a ...first application. The correspondence between the Monte Carlo integration and the analytic computation of NLO DGLAP evolution kernels is made explicit for both timelike and spacelike parton evolution. Numerical simulation results are obtained with two independent implementations of the new algorithm, using the two independent event generation frameworks PYTHIA and SHERPA.
A
bstract
We present a parton shower which implements the DGLAP evolution of parton densities and fragmentation functions at next-to-leading order precision up to effects stemming from local ...four-momentum conservation. The Monte-Carlo simulation is based on including next-to-leading order collinear splitting functions in an existing parton shower and combining their soft enhanced contributions with the corresponding terms at leading order. Soft double counting is avoided by matching to the soft eikonal. Example results from two independent realizations of the algorithm, implemented in the two event generation frameworks P
ythia
and S
herpa
, illustrate the improved precision of the new formalism.
We present a novel event-generation framework for the efficient simulation of vector boson plus multijet backgrounds at the high-luminosity LHC and at possible future hadron colliders. Message ...passing interface parallelization of parton-level and particle-level event generation and storage of parton-level event information using the HDF5 data format allow us to obtain leading-order merged Monte Carlo predictions with up to nine jets in the final state. The parton-level event samples generated in this manner correspond to an integrated luminosity of 3 ab−1 and are made publicly available for future phenomenological studies.
We present a new parton-shower algorithm. Borrowing from the basic ideas of dipole cascades, the evolution variable is judiciously chosen as the transverse momentum in the soft limit. This leads to a ...very simple analytic structure of the evolution. A weighting algorithm is implemented that allows one to consistently treat potentially negative values of the splitting functions and the parton distributions. We provide two independent, publicly available implementations for the two event generators P
ythia
and S
herpa
.
We present a Monte Carlo approach to soft-gluon resummation at subleading color which can be used to improve existing parton shower algorithms. At the single-emission level, soft-collinear ...enhancements of the splitting functions are explicitly linked to quadratic Casimir operators, while wide angle single-soft enhancements are connected to nontrivial color correlators. We focus on a numerically stable implementation of color matrix element corrections to all orders and approximate the virtual corrections by requiring unitarity at the single-emission level. We provide a proof-of-concept implementation to compute nonglobal event shapes at lepton colliders.
We compute the next-to-leading-order corrections to soft-gluon radiation differentially in the oneemission phase space. We show that their contribution to the evolution of color dipoles can be ...obtained in a modified subtraction scheme, such that both one- and two-emission terms are amenable to Monte Carlo integration. The two-loop cusp anomalous dimension is recovered naturally upon integration over the full phase space. We present two independent implementations of the new algorithm in the two event generators Pythia and Sherpa, and we compare the resulting fully differential simulation to the Catani–Marchesini– Webber (CMW) scheme.
We present a simple approach to combine NNLO QCD calculations and parten showers, based on the UNLOPS technique. We apply the method to the computation of Drell-Yan lepton-pair production at the ...Large Hadron Collider. We comment on possible improvements and intrinsic uncertainties.
We present a novel integrator based on normalizing flows which can be used to improve the unweighting efficiency of Monte Carlo event generators for collider physics simulations. In contrast to ...machine learning approaches based on surrogate models, our method generates the correct result even if the underlying neural networks are not optimally trained. We exemplify the new strategy using the example of Drell-Yan type processes at the LHC, both at leading and partially at next-to-leading order QCD.
A
bstract
In this publication, uncertainties in and differences between the M
C@NLO
and P
OWHEG
methods for matching next-to-leading order QCD calculations with parton showers are discussed. ...Implementations of both algorithms within the event generator S
HERPA
and based on Catani-Seymour subtraction are employed to assess the impact on a representative selection of observables. In the case of M
C@NLO
a substantial simplification is achieved by using dipole subtraction terms to generate the first emission. A phase space restriction is employed, which allows to vary in a transparent way the amount of non-singular radiative corrections that are exponentiated. Effects on various observables are investigated, using the production of a Higgs boson in gluon fusion, with or without an associated jet, as a benchmark process. The case of
H
+jet production is presented for the first time in an NLO+PS matched simulation. Uncertainties due to scale choices and non-perturbative effects are explored in the production of
W
±
and
Z
bosons in association with a jet. Corresponding results are compared to data from the Tevatron and LHC experiments.
PDF
