Kaleu is an independent, true phase space generator. After providing it with some information about the field theory and the particular multi-particle scattering process under consideration, it returns importance sampled random phase space points. Providing it also with the total weight of each generated phase space point, it further adapts to the integration problem on the fly. It is written in Fortran, such that it can independently deal with several scattering processes in parallel.
We develop a novel Monte Carlo parton branching algorithm based on the Gribov-Levin-Ryskin (GLR) equation. The formulations of both forward evolution and backward evolution for the GLR equation are presented. The results from the Monte Carlo implementation of the GLR equation are in full agreement with its numerical solutions. Our work thus paves the way for developing an event generator that embodies the saturation effect.
This article provides an introduction to the principles of particle physics event generators that are based on the Monte Carlo method. Following some preliminaries, instructions on how to build a basic parton-level Monte Carlo event generator for the hard interaction are given through exercises. Indications on how to proceed to full event simulations are given.
Evaluating parton density systematic uncertainties in Monte~Carlo event generator predictions has long been achieved by reweighting between the original and systematic PDFs for the initial state configurations of the individual simulated events. This weighting is now pre-emptively performed in many generators, providing convenient weight factors for PDF and scale systematics -- including for NLO calculations where counterterms make the weight calculation complex. This note attempts a pedagogical discussion and empirical study of the consequences of neglecting the effects of PDF variations on t…
We present the EpIC Monte Carlo event generator for exclusive processes sensitive to generalised parton distributions. EpIC utilises the PARTONS framework, which provides a flexible software architecture and a variety of modelling options for the partonic description of the nucleon. The generator offers a comprehensive set of features, including multi-channel capabilities and radiative corrections. It may be used both in analyses of experimental data, as well as in impact studies, especially for future electron-ion colliders.
We discuss prospects for Monte Carlo event generators incorporating the dynamics of transverse momentum dependent (TMD) parton distribution functions. We illustrate TMD evolution in the parton branching formalism, and present Monte Carlo applications of the method.
NNLOJET: a parton-level event generator for jet cross sections at NNLO QCD accuracy
CERN（欧洲核子研究组织）；Universität Zürich（苏黎世大学）；University of Durham（杜伦大学）；ETH（苏黎世联邦理工学院）；Shandong University（山东大学）；Max-Planck-Institut für Physik, Werner-Heisenberg-Institut（马克斯·普朗克物理研究所）；KIT（卡尔斯鲁厄理工学院）；TU Dresden（德累斯顿工业大学）；LIP（葡萄牙粒子与核物理研究所）；Universidade de Lisboa（里斯本大学）；University of Wuppertal（伍珀塔尔大学）；Georg-August-Universität Göttingen（哥廷根大学）
Parton shower event generators typically approximate evolution of QCD color so that only contributions that are leading in the limit of an infinite number of colors are retained. Our parton shower generator, Deductor, has used an "LC+" approximation that is better, but still quite limited. In this paper, we introduce a new scheme for color in which the approximations can be systematically improved. That is, one can choose the theoretical accuracy level, but the accuracy level that is practical is limited by the computer resources available.
The CASCADE3 Monte Carlo event generator based on Transverse Momentum Dependent (TMD) parton densities is described. Hard processes which are generated in collinear factorization with LO multileg or NLO parton level generators are extended by adding transverse momenta to the initial partons according to TMD densities and applying dedicated TMD parton showers and hadronization. Processes with off-shell kinematics within $k_t$-factorization, either internally implemented or from external packages via LHE files, can be processed for parton showering and hadronization. The initial state parton sho…
Transverse Momentum Dependent (TMD) parton distributions are a very powerful concept for the description of low and high transverse momentum effects in high energy collisions. The Parton Branching (PB) method provides TMD distributions which can be used in parton shower simulations, as already implemented in \cascade\ Monte Carlo event generator. This report gives a description of the work done during the DESY summer student program 2021, young scientists from very different time zones connecting from remote twice a day for 8 weeks, to develop a method, PS2TMD, that allows to determine effecti…
Parton branching methods underlie the Monte Carlo (MC) generators, being therefore of key importance for obtaining high energy physics predictions. We construct a new parton branching algorithm which for the first time incorporates the off-shell, transverse-momentum dependent (TMD) splitting functions, defined from the high-energy limit of partonic decay amplitudes. Based on these TMD splitting functions we construct a new TMD Sudakov form factor. We present the first MC implementation of the algorithm for the evolution of the TMD and integrated parton distribution functions (PDFs). We use thi…
Detailed and precise background predictions are the backbone of large parts of high-energy collider phenomenology. This requires to embed precision QCD calculations into detailed event generators, to produce comprehensive software simulations. Only continued progress in this direction will allow us to exploit the full potential of measurements at the Large Hadron Collider, or at a future Electron-Ion Collider. This work presents a method to combine third-order QCD calculations for hadronic scattering processes with Monte-Carlo event generators, thus enabling a new generation of precision predi…
PEGASUS is a parton-level Monte-Carlo event generator designed to calculate cross sections for a wide range of hard QCD processes at high energy $pp$ and $p\bar p$ collisions, which incorporates the dynamics of transverse momentum dependent (TMD) parton distributions in a proton. Being supplemented with off-shell production amplitudes for a number of partonic subprocesses and provided with necessary TMD gluon density functions, it produces weighted or unweighted event records which can be saved as a plain data file or a file in a commonly used Les Houches Event format. A distinctive feature of…
We consider idealized parton shower event generators that treat parton spin and color exactly, leaving aside the choice of practical approximations for spin and color. We investigate how the structure of such a parton shower generator is related to the structure of QCD. We argue that a parton shower with splitting functions proportional to $α_s$ can be viewed not just as a model, but as the lowest order approximation to a shower that is defined at any perturbative order. To support this argument, we present a formulation for a parton shower at order $α_s ^k$ for any $k$. Since some of the inpu…
In the present paper, we check and study the validity of the \textsc{KaTie} parton level event generator, by calculating the inclusive electron-proton (ep) dijet and the Proton-proton (p-p) Drell-Yan electron-pair productions differential cross sections in the $k_t$- and collinear factorization frameworks. The Martin-Ryskin-Watt (MRW) unintegrated parton distribution functions (UPDFs) are used as the input UPDFs. The results are compared with those of ZEUS ep inclusive dijet and ATLAS p-p Drell-Yan electron-pair productions, experimental data. The \textsc{KaTie} parton level event generator ca…
The search for new interactions and particles in high-energy collider physics relies on precise background predictions. This has led to many advances in combining precise fixed-order cross-section calculations with detailed event generator simulations. In recent years, fixed-order QCD calculations of inclusive cross sections at N3LO precision have emerged, followed by an impressive progress at producing differential results. Once differential results become publicly available, it would be prudent to embed these into event generators to allow the community to leverage these advances. This note …
We describe a Monte Carlo event generator for the production and decay of first and second string resonances through 2 $\rightarrow$ 2 partonic and also 2-parton $\rightarrow$ $γ$-parton scatterings in proton-proton collisions - STRINGS version 1.00. This generator is also capable of producing QCD diparton processes. STRINGS is written in Python 2 and can be interfaced to common hadronization programs using the Les Houches Accord.
