Related papers: Unitarising Matrix Element + Parton Shower merging
We consider the probability for a colour-singlet qqbar pair to emit a gluon, in strongly and smoothly ordered antenna showers. We expand to second order in alphaS and compare to the second-order QCD matrix elements for Z -> 3 jets,…
We extend the lowest-order matching of tree-level matrix elements with parton showers to give a complete description at the next higher perturbative accuracy in alpha_s at both small and large jet resolutions, which has not been achieved so…
We introduce an improvement to the FxFx matrix element merging procedure for $pp\to t \bar t W$ production at NLO in QCD with one and/or two additional jets. The main modification is an improved treatment of jets that are not…
The evolution of shower parton distributions in a jet is investigated in the framework of quark recombination model. The distributions are parameterized and the $Q^2$ dependence of the parameters is given by polynomials of $\ln Q^2$ for a…
We describe how to disentangle the singly- and doubly-unresolved (soft and/or collinear) limits of tree-level QCD squared matrix elements. Using the factorization formulae presented in this paper, we outline a viable general subtraction…
We present a general method to match fully differential next-to-next-to-leading (NNLO) calculations to parton shower programs. We discuss in detail the perturbative accuracy criteria a complete NNLO+PS matching has to satisfy. Our method is…
We present a Monte-Carlo approach to prompt-photon production, where photons and QCD partons are treated democratically. The photon fragmentation function is modelled by an interleaved QCD+QED parton shower. This known technique is improved…
We present a method of merging the exclusive LO-matched high energy resummation of High Energy Jets (HEJ) with the parton shower of Pythia which preserves the accuracy of the LO cross sections and the logarithmic accuracy of both…
One can use more than one scale variable to define the family of surfaces in the space of parton splitting parameters that define the evolution of a parton shower. In an earlier paper, we developed this idea for electron-positron…
QCD jets are considered important probes for quark gluon plasma created in collisions of nuclei at high energies. Their parton showers are significantly altered if they develop inside of a deconfined medium. Hadronization of jets is also…
We have previously described a mathematical formulation for a parton shower based on the approximation of strongly ordered virtualities of successive parton splittings. Quantum interference, including interference among different color and…
Jet substructure is typically studied using clustering algorithms, such as kT, which arrange the jets' constituents into trees. Instead of considering a single tree per jet, we propose that multiple trees should be considered, weighted by…
We present an algorithm to evaluate the exact, tree-level matrix elements for multi-parton processes in QCD. We tested this technique, based on the recursive evaluation of the S-matrix, on processes such as gg -> n gluons and q qbar -> n…
We present an antenna-shower formalism that includes helicity dependence for massless partons. The formalism applies to both traditional (global) showers and to sector-based variants. We combine the shower with VINCIA's multiplicative…
We present the implementation and validation of the techniques used to efficiently evaluate parametric and perturbative theoretical uncertainties in matrix-element plus parton-shower simulations within the Sherpa event-generator framework.…
The Parton-Shower algorithm implement in the Pythia generator is applied multiple times to the same parton-level configuration to estimate the systematic uncertainty affecting large-radius jet substructure variables associated with the…
We discuss an alternative subtraction scheme for NLO QCD calculations, which is based on the splitting kernels of an improved parton shower. As an example, we show results for the C parameter of the process e+ e- to 3 jets at NLO used for…
We propose a new way to impose four-momentum conservation on timelike parton-shower branchings, allowing for recoil to be imparted not only to individual partons but also to groups of partons, "jets". In this work we present an explicit…
We present a method to match the multi-parton states generated by the High Energy Jets Monte Carlo with parton showers generated by the Ariadne program using the colour dipole model. The High Energy Jets program already includes a full…
We illustrate a study based on a veto technique to match parton showers and matrix elements in the Cascade Monte Carlo event generator, and present a numerical application to gluon matrix elements for jet production.