Innovative Network for Monte Carlo Event Generators for LHC Physics

Project Information

MCnetITN3

Grant agreement ID: 722104

DOI

10.3030/722104

Project closed

EC signature date 31 August 2016

Start date 1 April 2017

End date 31 December 2021

Funded under

• EXCELLENT SCIENCE - Marie Skłodowska-Curie Actions

Total cost

€ 3 929 950,71

EU contribution

€ 3 929 950,71

Coordinated by

THE UNIVERSITY OF MANCHESTER
United Kingdom

Periodic Reporting for period 2 - MCnetITN3 (Innovative Network for Monte Carlo Event Generators for LHC Physics)

Reporting period: 2019-04-01 to 2021-12-31

Summary of the context and overall objectives of the project

MCnetITN3 is an Innovative Training Network dedicated to developing and supporting general-purpose Monte Carlo event generators throughout the LHC era and beyond, training the next generation of event generator developers and providing training of a wide selection of its user base, particularly through funded short-term 'residencies' and Annual Schools.

Monte Carlo event generators are computer programs that simulate the final states of high energy particle collisions, and are central to particle physics. They are used by almost all experimental collaborations to plan their experiments and analyze their data, and by theorists to simulate the complex final states of the fundamental interactions that may signal new physics.

The network consists of the Universities of Manchester, Durham, Glasgow, Göttingen, Louvain and Lund, University College London and the Karlsruhe Institute of Technology, joined by academic partners CERN, Fermilab, Heidelberg, Monash (Australia) and Vienna and non-academic partners B12, Blue Yonder, d-fine and Ion Beam Applications.

Our training programme was implemented through the recruitment of 11 long-term Early Stage Researchers to complete PhDs in Monte Carlo event generator physics, techniques and related disciplines, and of 144 ESR-months of short-term positions, whereby students registered for a PhD elsewhere could receive complementary training by working in one of our groups for three to six months, and through Annual Schools in Europe both for our own ESRs and for the external community, as well as two schools outside Europe, annual training events for our ESRs and bi-annual network meetings. The long-term ESRs have all been offered non-academic secondments in one of our partners, as well as academic secondments as part of their ongoing research.

Our research programme is divided into six sub-projects, three of which develop fully-fledged general purpose event generators (Pythia, Herwig and Sherpa) capable of simulating all the stages of a high-energy particle collision, two of which develop more specialised simulations of specific event generator steps (Madgraph and Plugin, which includes sub-projects Ariadne/DIPSY and HEJ) and one of which (CEDAR) develops a suite of programs related to the deployment and optimisation of these generators for particle physics experiments and analysis.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

9 of our 11 long-term ESRs have completed their PhD theses - the other two are close to completion. 30 short-term students completed projects in our groups. We held 4 Annual Schools in Europe, 1 in Vietnam and 1 in China, 4 employability training events, 2 scientific computing schools and 9 Network Meetings. ESRs have undertaken secondments with our academic and non-academic Partners.

All of our event generator development projects have released versions with significant new features, improving the precision and scope of simulation for collider physics experiments, particularly the LHC.

The Pythia sub-project has extended its successful simulation of proton-proton collisions to the collisions of nuclei ("heavy ions") either with protons or with each other. It has also made important improvements in the accuracy of the parton shower process and the non-perturbative processes that convert partons into the hadrons seen in experiments. An earlier Pythia paper has reached the outstanding milestone of 12,000 citations.

The Herwig sub-project has implemented an automated algorithm for merging higher order matrix elements with its parton shower algorithms, as well as key improvements to these shower algorithms. It has also experimented with a simple model to extend its simulation to heavy ion collisions, and made non-perturbative, perturbative and electroweak improvements.

The Sherpa sub-project was the first to demonstrate next-to-next-to-leading order accuracy and generalisations of this are ongoing. It has generalised its QCD machinery to electroweak corrections, and improved its treatment of mass effects in matrix elements and parton showers.

The Madgraph sub-project has made important progress in the simulation of physics Beyond the Standard Model, particularly in parametrising such physics through effective field theories, and also in the simulation of Dark Matter. Modules have been developed to simulate future experiments that search for new physics in high intensity "beam dump" collisions, and multi-TeV lepton colliders.

The Plugin sub-project consists of several projects. In Ariadne/DIPSY, a new model has been developed to account for collective phenomena in heavy ion and proton collisions. HEJ is aimed at describing processes in LHC collisions where many jets are produced well separated from each other with similar momentum scales. Its formal accuracy has been extended to next-to-leading order and it has been merged consistently with a parton shower.

The CEDAR sub-project is an umbrella for an array of projects focussed on optimal use of event generators for particle physics experiments. Most active have been Rivet (which provides tools to validate event generators against existing data) and Contur (which similarly evaluates new physics models against existing data), with progress also on LHAPDF (providing parton distribution functions), YODA and HepMC. Important developments have also been made here for heavy ion collisions.

Important inter-project collaboration has also taken place on electroweak corrections, loop-induced processes, heavy ion collisions, parton shower improvements and high-performance computing implementations.

Covid forced many of our activities online and required an extension to the network period, but in the end all of our research and training was completed as planned.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

All of the event generator projects already represented the state of the art in the simulation of high energy particle collisions. They have now extended their revolutionary progress to higher precision, particularly in the merging of the parton shower approach with matrix element calculations performed at ever higher accuracy. They are also the only tools to simulate non-perturbative transitions between partonic and hadronic degrees of freedom in particle collisions and progress here has included the further extension of current treatments to heavy ion collisions and high-multiplicity proton collisions, in which collective phenomena appear to play a role.

The primary impacts are through the better understanding and exploitation of LHC data, and through the deeper training of ESRs, many of whom are going on to careers outside our immediate field. The LHC is one of the highest-profile scientific experiments in history, and highly influential in the public's perception of science, and in attracting young people to study science, many of whom go on to careers that apply their scientific knowledge and approach to societal problems (three of our non-academic partners were founded by particle physics PhDs, and all four recruit heavily from our field). The LHC's headline achievements would have been impossible without the simulations provided by MCnetITN3's projects and as such we have a major impact. The accuracy of many LHC analyses has outstripped the theory predictions with which they are compared and MCnetITN3 has addressed this balance by a significant upgrade to the accuracy of the simulations. This leaves a legacy of impact beyond our field and well beyond the funding period.

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