Event Generation Framework Research Articles

Generalized angular-order parton showers in Herwig 7

This paper presents the inaugural investigation of beyond the Standard Model (BSM) radiation processes, framed as a generalized, process- and model-independent parton shower algorithm within Herwig 7, based on direct translations of Universal FeynRules Output (UFO) constructed via Herwig’s ufo2herwig module. Leveraging the fact that shower kinematics are dictated by the spins of involved particles, we calculate comprehensive helicity-dependent branching kernels for all feasible splittings of scalars, fermions, and vector bosons, tailored to Herwig 7’s angular-ordering (AO) parton shower algorithm. Utilizing these kernels, we derive BSM splitting functions in the quasi-collinear limit, ensuring compatibility with the Standard Model (SM) and supersymmetry (SUSY) splitting functions when analogous parameter conditions are applied. These newly derived functions have been integrated into the Herwig 7 event generator framework. Comparative analyses with fixed-order matrix element calculations show good agreement for single radiation events. Moreover, the results showcase the influence of BSM radiation at the Large Hadron Collider (LHC) and envisage its implications for future collider endeavours. This research augments our comprehension of BSM radiation effects, with significant bearings on present and prospective collider-based inquiries.

Design of a pollution ontology-based event generation framework for the dynamic application of traffic restrictions.

The environmental damage caused by air pollution has recently become the focus of city council policies. The concept of the green city has emerged as an urban solution by which to confront environmental challenges worldwide and is founded on air pollution levels that have increased meaningfully as a result of traffic in urban areas. Local governments are attempting to meet environmental challenges by developing public traffic policies such as air pollution protocols. However, several problems must still be solved, such as the need to link smart cars to these pollution protocols in order to find more optimal routes. We have, therefore, attempted to address this problem by conducting a study of local policies in the city of Madrid (Spain) with the aim of determining the importance of the vehicle routing problem (VRP), and the need to optimise a set of routes for a fleet. The results of this study have allowed us to propose a framework with which to dynamically implement traffic constraints. This framework consists of three main layers: the data layer, the prediction layer and the event generation layer. With regard to the data layer, a dataset has been generated from traffic data concerning the city of Madrid, and deep learning techniques have then been applied to this data. The results obtained show that there are interdependencies between several factors, such as weather conditions, air quality and the local event calendar, which have an impact on drivers' behaviour. These interdependencies have allowed the development of an ontological model, together with an event generation system that can anticipate changes and dynamically restructure traffic restrictions in order to obtain a more efficient traffic system. This system has been validated using real data from the city of Madrid.

Machine learning efforts in Sherpa

Modern machine learning methods offer great potential for increasing the efficiency of Monte Carlo event generators. We present the latest developments in the context of the SHERPA event generation framework. These include phase space sampling amended by normalizing flows and a new unweighting procedure based on neural-network surrogates for the full matrix elements. We discuss corresponding general construction criteria and show examples of efficiency gains for selected LHC production processes.

Novel event generator for the automated simulation of neutrino scattering

An event generation framework is presented that enables the automatic simulation of events for next-generation neutrino experiments in the Standard Model or extensions thereof. The new generator combines the calculation of the leptonic current based on an automated matrix element generator and the computation of the hadronic current based on a state-of-the-art nuclear physics model. The approach is validated in Standard Model simulations for electron scattering and neutrino scattering. Furthermore, the first fully differential neutrino trident production results are shown in the quasielastic region.

Soft-drop grooming for hadronic event shapes

Soft-drop grooming of hadron-collision final states has the potential to significantly reduce the impact of non-perturbative corrections, and in particular the underlying-event contribution. This eventually will enable a more direct comparison of accurate perturbative predictions with experimental measurements. In this study we consider soft-drop groomed dijet event shapes. We derive general results needed to perform the resummation of suitable event-shape variables to next-to-leading logarithmic (NLL) accuracy matched to exact next-to-leading order (NLO) QCD matrix elements. We compile predictions for the transverse-thrust shape accurate to NLO + NLL′ using the implementation of the Caesar formalism in the Sherpa event generator framework. We complement this by state-of-the-art parton- and hadron-level predictions based on NLO QCD matrix elements matched with parton showers. We explore the potential to mitigate non-perturbative corrections for particle-level and track-based measurements of transverse thrust by considering a wide range of soft-drop parameters. We find that soft-drop grooming indeed is very efficient in removing the underlying event. This motivates future experimental measurements to be compared to precise QCD predictions and employed to constrain non-perturbative models in Monte-Carlo simulations.

Automated evaluation of electroweak Sudakov logarithms in SHERPA

We present an automated implementation for the calculation of one-loop double and single Sudakov logarithms stemming from electroweak radiative corrections within the SHERPA event generation framework, based on the derivation in Denner and Pozzorini (Eur Phys J C 18:461–480, 2001). At high energies, these logarithms constitute the leading contributions to the full NLO electroweak corrections. As examples, we show applications for relevant processes at both the LHC and future hadron colliders, namely on-shell W boson pair production, EW-induced dijet production and electron–positron production in association with four jets, providing the first estimate of EW corrections at this multiplicity.

Simulation of vector boson plus many jet final states at the high luminosity LHC

We present a novel event generation framework for the efficient simulation of vector boson plus multi-jet backgrounds at the high-luminosity LHC and at possible future hadron colliders. MPI 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 3ab-1 and are made publicly available for future phenomenological studies.

Hadronic final states in DIS at NNLO QCD with parton showers

We present a parton-shower matched NNLO QCD calculation for hadronic final state production in Deep Inelastic Scattering. The computation is based on the UNLOPS method and is implemented in the publicly available event generation framework SHERPA. Results are compared to measurements performed by the H1 collaboration.

A practical guide to event generation for prompt photon production with Sherpa

The production of prompt photons is one of the most relevant scattering processes studied at hadron–hadron colliders in recent years. This article will give an overview of the different approaches used to simulate prompt photon production in the Sherpa event generator framework. Special emphasis is placed on a complete simulation of this process including fragmentation configurations. As a novel application a merged simulation of and jet production at NLO accuracy is presented and compared to measurements from the ATLAS experiment.

The STAR "plug and play" event generator framework

The STAR experiment pursues a broad range of physics topics in pp,pA and AA collisions produced by the Relativistic Heavy Ion Collider (RHIC). Such a diverse experimental program demands a simulation framework capable of supporting an equally diverse set of event generators, and a flexible event record capable of storing the (common) particle-wise and (varied) event-wise information provided by the external generators. With planning underway for the next round of upgrades to exploit ep and eA collisions from the electron-ion collider (or eRHIC), these demands on the simulation infrastructure will only increase and requires a versatile framework. STAR has developed a new event-generator framework based on the best practices in the community (a survey of existing approach had been made and the "best of all worlds" kept in mind in our design). It provides a common set of base classes which establish the interface between event generators and the simulation and handles most of the bookkeeping associated with a simulation run. This streamlines the process of integrating and configuring an event generator within our software chain. Developers implement two classes: the interface for their event generator, and their event record. They only need to loop over all particles in their event and push them out into the event record. The framework is responsible for vertex assignment, stacking the particles out for simulation, and event persistency. Events from multiple generators can be merged together seamlessly, with an event record which is capable of tracing each particle back to its parent generator. We present our work and approach in detail and illustrate its usefulness by providing examples of event generators implemented within the STAR framework covering for very diverse physics topics. We will also discuss support for event filtering, allowing users to prune the event record of particles which are outside of our acceptance, and/or abort events prior to the more computationally expensive digitization and reconstruction phases. Event filtering has been supported in the previous framework and showed to save enormous amount of resources – the approach within the new framework is a generalization of filtering.

Soft photon radiation in particle decays in SHERPA

In this paper the Yennie–Frautschi–Suura approach is used to simulate real and virtual QED corrections in particle decays. It makes use of the universal structure of soft photon corrections to resum the leading logarithmic QED corrections to all orders, and it allows a systematic correction of this approximate result to exact fixed order results from perturbation theory. The approach has been implemented as a Monte Carlo algorithm, which a posteriori modifies decay matrix elements through the emission of varying numbers of photons. The corresponding computer code is incorporated into the SHERPA event generator framework.

APACIC++ 2.0. A PArton Cascade In C++

The new version of the parton shower module APACIC++ for the SHERPA event generator framework is presented. It incorporates some features, that are specific for the consistent merging with multi-particle matrix elements at tree-level. This publication also includes some example results and a short description of the upgraded class structure of APACIC++, version 2.0. Program summary Title of program: APACIC++, version 2.0 Catalogue identifier:ADNE_v2_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/ADNE_v2_0 Program obtainable from: CPC Program Library, Queen's University of Belfast, N. Ireland Catalogue identifier of previous version: ADNE Authors of previous version: R. Kuhn, F. Krauss, B. Iványi, G. Soff Journal reference of previous version: Comput. Phys. Commun. 134 (2001) 223 Licensing provisions: none Operating system under which the program has been tested: Linux, Unix, Darwin Programming language: C++ No. of lines in distributed program, including test data, etc.: 78 352 No. of bytes in distributed program, including test data, etc.: 2 561 276 External routines/libraries used: The makeinstall requires the autotools package Distribution format: tar gzip file Nature of the physical problem: Modern collider-based experiments in particle physics are characterized by increasing energies that are released and, thus, by a growing number of particles that are produced. The large numbers of involved particles renders it impossible to derive fully analytical predictions for a detailed description of the final state. In addition, the transformation of the partons of perturbative quantum field theory into the experimentally observable hadrons is until now not understood on a quantitative level. These obstacles prevent a direct comparison of analytical predictions with experimental data, and simulation tools need to be employed to bridge this gap. Method of solution: The event generator SHERPA with a new version of the parton shower module APACIC++ is able to simulate e + e − -annihilation experiments as well as hadron–hadron collision. The generated events are suitable for direct comparison with experiment. This is achieved by dividing the simulation into well-separated steps. First, the signal process is selected by employing multi-particle matrix elements at tree-level. Then the strong interacting particles experience additional radiation of soft or collinear partons described by means of the parton shower. Finally, the partons are translated into observable hadrons using phenomenological models. The module APACIC++ concentrates on the parton shower evolution of jets, both in the initial and in the final state of the signal process. Suitable interfaces to other modules of the event generator SHERPA are provided. Reasons for the new version: This new version is able to perform not only final state shower but also initial state shower evolutions. Thus the program gives now also a realistic description of proton–proton and proton–anti-proton collisions. It is particularly designed to simulate events at the Tevatron or the LHC. Summary of revisions: The package has been extended by a number of classes for the description of the initial state shower. In order to give optimal support for these new routines, all existing classes of the final state shower have been revised, but the basic structure and concept of the program has been maintained. In addition a new dicing strategy has been introduced in the time-like evolution routine, which substantially improved the performance of the final state shower. Additional comments: The package APACIC++ is used as the parton shower module of the general purpose event generator SHERPA. There it takes full advantage of its capabilities to merge multi-jet matrix element and parton shower evolution. Running time: The example programs take a matter of seconds to run.

Event generator for the LHC

In this contribution the new event generation framework S herpa will be presented. It aims at the full simulation of events at current and future high-energy experiments, in particular the LHC. Some results related to the production of jets at the Tevatron will be discussed.