Showing 1–50 of 122 results for author: Richardson, P

Polarized Deep-Inelastic Scattering with Spin Correlations in Herwig 7

Authors: M. R. Masouminia, A. Papaefstathiou, P. Richardson

Abstract: We investigate polarized deep-inelastic scattering (DIS) in the context of fully exclusive Monte Carlo simulations for the Electron-Ion Collider (EIC). We present a next-to-leading-order (NLO) treatment of polarized DIS in HERWIG 7 using the POWHEG matching scheme, including neutral-current $γ/Z$ exchange and charged-current scattering. We also construct a spin-correlation treatment for NLO-matche… ▽ More We investigate polarized deep-inelastic scattering (DIS) in the context of fully exclusive Monte Carlo simulations for the Electron-Ion Collider (EIC). We present a next-to-leading-order (NLO) treatment of polarized DIS in HERWIG 7 using the POWHEG matching scheme, including neutral-current $γ/Z$ exchange and charged-current scattering. We also construct a spin-correlation treatment for NLO-matched events, first by initializing the shower from the spin-density matrix of the polarized DIS Born process and then by propagating the spin-density matrix of the accepted real-emission configuration without changing the POWHEG event weight or hardest-emission choice. We validate the integrated cross sections against fixed-order calculations, use parton-level comparisons without subsequent shower evolution to isolate the accepted POWHEG real-emission kinematics, and employ shower-level observables to test the numerical importance of the Born-level and real-emission spin information. We find that the Born-level spin-density initialization can have a visible impact on shower-sensitive observables, while the additional spin information from the accepted real-emission configuration is not resolved as a robust separate effect within the independent-sample Monte Carlo precision for the longitudinally polarized observables considered here. △ Less

Submitted 12 August, 2026; v1 submitted 22 June, 2026; originally announced June 2026.

Comments: 55 pages, 17 figures, 6 tables. Updated shower-spin study using independent physical-helicity samples and covariance-aware uncertainties; replaced the spin-correlation figures and clarified the associated conclusions. Corrected the report number and NNLO references

Report number: IPPP-26-47, MCnet-26-17

Reproducible Synthetic Clinical Letters for Seizure Frequency Information Extraction

Authors: Yujian Gan, Stephen H. Barlow, Ben Holgate, Joe Davies, James T. Teo, Joel S. Winston, Mark P. Richardson

Abstract: Seizure-frequency information is important for epilepsy research and clinical care, but it is usually recorded in variable free-text clinic letters that are hard to annotate and share. We developed a reproducible, privacy-preserving framework for extracting seizure frequency using fully synthetic yet task-faithful epilepsy letters. We defined a structured label scheme covering common descriptions… ▽ More Seizure-frequency information is important for epilepsy research and clinical care, but it is usually recorded in variable free-text clinic letters that are hard to annotate and share. We developed a reproducible, privacy-preserving framework for extracting seizure frequency using fully synthetic yet task-faithful epilepsy letters. We defined a structured label scheme covering common descriptions of seizure burden, including explicit rates, ranges, clusters, seizure-free intervals, unknown frequency, and explicit no-seizure statements. A teacher language model generated NHS-style synthetic letters paired with normalized labels, rationales, and evidence spans. We fine-tuned several open-weight language models (4B-14B parameters) on these synthetic letters to extract seizure frequency from full documents, comparing direct numeric prediction with structured label prediction and testing evidence-grounded outputs. On a clinician-checked held-out set of real clinic letters, models trained only on synthetic data generalized well, and structured labels consistently outperformed direct numeric regression. With 15,000 synthetic training letters, models achieved micro-F1 scores up to 0.788 for fine-grained categories and 0.847 for pragmatic categories; a medically oriented 4B model achieved 0.787 and 0.858, respectively. Evidence-grounded outputs also supported rapid clinical verification and error analysis. These results show that synthetic, structured, evidence-grounded supervision can enable robust seizure-frequency extraction without sharing sensitive patient text and may generalize to other temporally complex clinical information extraction tasks. △ Less

Submitted 11 March, 2026; originally announced March 2026.

Gauge-Invariant Longitudinal Modes in the Herwig 7 Electroweak Parton Shower

Authors: M. R. Masouminia, P. Richardson

Abstract: Longitudinal electroweak gauge bosons are the most technically delicate ingredient of electroweak parton showers: in the broken Standard Model, the gauge component of a longitudinal polarisation does not cancel diagram by diagram, but is related by Ward identities to amplitudes with an insertion of the associated would-be Goldstone field. Building on the default Herwig 7 treatment based on a subtr… ▽ More Longitudinal electroweak gauge bosons are the most technically delicate ingredient of electroweak parton showers: in the broken Standard Model, the gauge component of a longitudinal polarisation does not cancel diagram by diagram, but is related by Ward identities to amplitudes with an insertion of the associated would-be Goldstone field. Building on the default Herwig 7 treatment based on a subtraction-defined longitudinal current, we construct a gauge-invariant scheme in which the subtraction remainder is retained as a well-defined contribution and completed by a Ward-identity-fixed Goldstone-matching term. We derive helicity-resolved building blocks and compact quasi-collinear splitting kernels for $q\to q'V$ and $V\to V'V''$ branchings, and implement the scheme in Herwig 7 as a switchable alternative to the default basis. The completion leaves the transverse sector unchanged and modifies only longitudinal entries through controlled symmetry-breaking terms, including Yukawa-sensitive contributions in massive-fermion channels. In shower-level studies, we find that the default and gauge-invariant prescriptions coincide at high evolution scales, while differing at lower scales precisely in channels where symmetry breaking is active. Exclusive single-emission observables can moreover display non-monotonic scheme dependence once Sudakov suppression and kinematic constraints are accounted for. A first multi-emission LHC-like study confirms numerical stability and yields controlled, interpretable shifts in observables that probe propagating electroweak shower currents, whereas quantities dominated by promptly contracted, near on-shell vector-boson matrix elements remain largely unchanged. △ Less

Submitted 18 March, 2026; v1 submitted 23 February, 2026; originally announced February 2026.

Comments: 24 pages, 8 figures and 2 tables

Report number: IPPP/25/91

The Physics of Herwig 7

Authors: J. Bellm, G. Bewick, S. Ferrario Ravasio, S. Gieseke, D. Grellscheid, S. Kiebacher, P. Kirchgaeßer, F. Loshaj, M. R. Masouminia, G. Nail, A. Papaefstathiou, S. Plätzer, M. Rauch, P. Reimitz, C. Reuschle, P. Richardson, D. Samitz, P. Sarmah, P. Schichtel, M. H. Seymour, A. Siódmok, D. Stafford, C. B. Strange, S. Sule, S. Webster , et al. (1 additional authors not shown)

Abstract: We present the physics foundations and recent developments of Herwig 7, the modern successor of the original HERWIG and Herwig++ series. Herwig 7 provides a flexible and systematically improvable framework for the simulation of high-energy lepton and hadron collisions, with particular emphasis on QCD and EW effects. Hard scattering processes are generated within the automated Matchbox framework, w… ▽ More We present the physics foundations and recent developments of Herwig 7, the modern successor of the original HERWIG and Herwig++ series. Herwig 7 provides a flexible and systematically improvable framework for the simulation of high-energy lepton and hadron collisions, with particular emphasis on QCD and EW effects. Hard scattering processes are generated within the automated Matchbox framework, which integrates external amplitude providers, supports tree-level, next-to-leading-order (NLO) and loop-induced matrix elements, and implements subtraction schemes, multi-channel phase-space sampling, dynamic scale choices and both POWHEG- and MC@NLO-type matching algorithms. Consistent multijet merging at LO and NLO is provided, enabling precise predictions across a wide range of SM processes. Parton radiation is simulated using two complementary showers: an angular-ordered shower incorporating QCD coherence and the heavy-quark dead-cone effect, and a dipole shower optimised for NLO matching and multijet merging. Higher-order corrections are included through matrix-element corrections and dedicated reweighting techniques, while QED and EW radiation are treated using a YFS formalism and EW showering algorithms. The modelling of non-perturbative physics employs an advanced cluster hadronization framework with improved cluster formation, fission and decay, as well as colour reconnection models, heavy-quark effects and interfaces to alternative hadronization schemes. An extended eikonal multiple-partonic-scattering model, incorporating semi-hard and soft components together with diffractive interactions, enables realistic descriptions of minimum-bias and underlying-event data. Herwig 7 thus represents a versatile event generator, providing a coherent, modular and extensible platform for Standard Model and beyond-the-Standard-Model collider phenomenology at current and future facilities. △ Less

Submitted 18 December, 2025; originally announced December 2025.

Comments: 195 page, 476 references

Report number: CERN-TH-2025-252, IPPP-25-57, HERWIG-2025-01, KA-TP-36-2025, MCNET-25-31

Quarkonium Parton Shower in Herwig 7

Authors: M. R. Masouminia, P. Richardson

Abstract: We present the implementation of a fully automated quarkonium parton shower in Herwig 7, based on non-relativistic QCD (NRQCD) factorisation with spin-colour projections. The framework systematically incorporates colour-singlet and colour-octet production mechanisms, gluon fragmentation, and diquark production processes. Perturbative short-distance coefficients are combined with non-perturbative N… ▽ More We present the implementation of a fully automated quarkonium parton shower in Herwig 7, based on non-relativistic QCD (NRQCD) factorisation with spin-colour projections. The framework systematically incorporates colour-singlet and colour-octet production mechanisms, gluon fragmentation, and diquark production processes. Perturbative short-distance coefficients are combined with non-perturbative NRQCD matrix elements to simulate heavy-quark bound state formation. Splitting functions for $S$-, $P$- and $D$-wave states are explicitly derived and integrated into the angular-ordered shower evolution. The implementation preserves spin correlations and polarisation effects while accurately accounting for feed-down contributions. Results demonstrate improved agreement with the existing LHC data. This quarkonium parton shower will become publicly available with the release of Herwig-7.4.0. △ Less

Submitted 8 August, 2025; originally announced August 2025.

Comments: 39 pages, 12 figures and 5 tables

Report number: IPPP/25/06

Photoproduction in general-purpose event generators

Authors: Ilkka Helenius, Peter Meinzinger, Simon Plätzer, Peter Richardson

Abstract: We compare the three general-purpose Monte Carlo event generators, HERWIG, PYTHIA, and SHEPRA for jet photoproduction processes in $e^+e^-$ and $ep$ collisions. Due to the lower energy scales probed, photoproduction is particularly sensitive to non-perturbative corrections. In a systematic analysis we disentangle and quantify the differences between the generators in these processes, i.e. contribu… ▽ More We compare the three general-purpose Monte Carlo event generators, HERWIG, PYTHIA, and SHEPRA for jet photoproduction processes in $e^+e^-$ and $ep$ collisions. Due to the lower energy scales probed, photoproduction is particularly sensitive to non-perturbative corrections. In a systematic analysis we disentangle and quantify the differences between the generators in these processes, i.e. contributions from beam remnants, parton showers, multiparton interactions (MPIs), and hadronisation modelling. We outline the default inputs and implementation differences and compare the computations with experimental data from LEP and HERA. We find that all generators provide a decent description of the data within the uncertainties, with particularly good descriptions by the LO-accurate PYTHIA and the NLO-accurate SHERPA. Finally, we also present predictions for the upcoming EIC for jet observables and event shapes and conclude that a modern global refit of the photon parton distributions and dedicated experimental measurements ported to the RIVET framework to constrain non-perturbative parameters are the key prerequisites for precision photoproduction phenomenology at the EIC. △ Less

Submitted 9 April, 2026; v1 submitted 12 June, 2024; originally announced June 2024.

Comments: 21 pages, 15 figures; accepted version

Report number: IPPP/24/30

Journal ref: SciPost Phys. Comm. Rep. 23 (2026)

Robust Independent Validation of Experiment and Theory: Rivet version 4 release note

Authors: Christian Bierlich, Andy Buckley, Jonathan Butterworth, Christian Gutschow, Leif Lonnblad, Tomasz Procter, Peter Richardson, Yoran Yeh

Abstract: The Rivet toolkit is the primary mechanism for phenomenological preservation of collider-physics measurements, containing both a computational core and API for analysis implementation, and a large collection of more than a thousand preserved analyses. In this note we summarise the main changes in the new Rivet 4 major release series. These include a major generalisation and more semantically coher… ▽ More The Rivet toolkit is the primary mechanism for phenomenological preservation of collider-physics measurements, containing both a computational core and API for analysis implementation, and a large collection of more than a thousand preserved analyses. In this note we summarise the main changes in the new Rivet 4 major release series. These include a major generalisation and more semantically coherent model for histograms and related data objects, a thorough clean-up of inelegant and legacy observable-computation tools, and new systems for extended analysis-data, incorporation of preserved machine-learning models, and serialization for high-performance computing applications. Where these changes introduce backward-incompatible interface changes, existing analyses have been updated and indications are given on how to update new analysis routines and workflows. △ Less

Submitted 13 August, 2024; v1 submitted 24 April, 2024; originally announced April 2024.

Report number: MCNET-24-05

Multimodal wearable EEG, EMG and accelerometry measurements improve the accuracy of tonic-clonic seizure detection in-hospital

Authors: Jingwei Zhang, Lauren Swinnen, Christos Chatzichristos, Victoria Broux, Renee Proost, Katrien Jansen, Benno Mahler, Nicolas Zabler, Nino Epitashvilli, Matthias Dümpelmann, Andreas Schulze-Bonhage, Elisabeth Schriewer, Ummahan Ermis, Stefan Wolking, Florian Linke, Yvonne Weber, Mkael Symmonds, Arjune Sen, Andrea Biondi, Mark P. Richardson, Abuhaiba Sulaiman I, Ana Isabel Silva, Francisco Sales, Gergely Vértes, Wim Van Paesschen , et al. (1 additional authors not shown)

Abstract: Objective: Most current wearable tonic-clonic seizure (TCS) detection systems are based on extra-cerebral signals, such as electromyography (EMG) or accelerometry (ACC). Although many of these devices show good sensitivity in seizure detection, their false positive rates (FPR) are still relatively high. Wearable EEG may improve performance; however, studies investigating this remain scarce. This p… ▽ More Objective: Most current wearable tonic-clonic seizure (TCS) detection systems are based on extra-cerebral signals, such as electromyography (EMG) or accelerometry (ACC). Although many of these devices show good sensitivity in seizure detection, their false positive rates (FPR) are still relatively high. Wearable EEG may improve performance; however, studies investigating this remain scarce. This paper aims 1) to investigate the possibility of detecting TCSs with a behind-the-ear, two-channel wearable EEG, and 2) to evaluate the added value of wearable EEG to other non-EEG modalities in multimodal TCS detection. Method: We included 27 participants with a total of 44 TCSs from the European multicenter study SeizeIT2. The multimodal wearable detection system Sensor Dot (Byteflies) was used to measure two-channel, behind-the-ear EEG, EMG, electrocardiography (ECG), ACC and gyroscope (GYR). First, we evaluated automatic unimodal detection of TCSs, using performance metrics such as sensitivity, precision, FPR and F1-score. Secondly, we fused the different modalities and again assessed performance. Algorithm-labeled segments were then provided to a neurologist and a wearable data expert, who reviewed and annotated the true positive TCSs, and discarded false positives (FPs). Results: Wearable EEG outperformed the other modalities in unimodal TCS detection by achieving a sensitivity of 100.0% and a FPR of 10.3/24h (compared to 97.7% sensitivity and 30.9/24h FPR for EMG; 95.5% sensitivity and 13.9 FPR for ACC). The combination of wearable EEG and EMG achieved overall the most clinically useful performance in offline TCS detection with a sensitivity of 97.7%, a FPR of 0.4/24 h, a precision of 43.0%, and a F1-score of 59.7%. Subsequent visual review of the automated detections resulted in maximal sensitivity and zero FPs. △ Less

Submitted 19 March, 2024; originally announced March 2024.

Herwig 7.3 Release Note

Authors: Gavin Bewick, Silvia Ferrario Ravasio, Stefan Gieseke, Stefan Kiebacher, Mohammad R. Masouminia, Andreas Papaefstathiou, Simon Plätzer, Peter Richardson, Daniel Samitz, Michael H. Seymour, Andrzej Siódmok, James Whitehead

Abstract: A new release of the Monte Carlo event generator Herwig (version 7.3) has been launched. This iteration encompasses several enhancements over its predecessor, version 7.2. Noteworthy upgrades include: the implementation of a process-independent electroweak angular-ordered parton shower integrated with QCD and QED radiation; a new recoil scheme for initial-state radiation improving the behaviour of… ▽ More A new release of the Monte Carlo event generator Herwig (version 7.3) has been launched. This iteration encompasses several enhancements over its predecessor, version 7.2. Noteworthy upgrades include: the implementation of a process-independent electroweak angular-ordered parton shower integrated with QCD and QED radiation; a new recoil scheme for initial-state radiation improving the behaviour of the angular-ordered parton shower; the incorporation of the heavy quark effective theory to refine the hadronization and decay of excited heavy mesons and heavy baryons; a dynamic strategy to regulate the kinematic threshold of cluster splittings within the cluster hadronization model; several improvements to the structure of the cluster hadronization model allowing for refined models; the possibility to extract event-by-event hadronization corrections in a well-defined way; the possibility of using the string model, with a dedicated tune. Additionally, a new tuning of the parton shower and hadronization parameters has been executed. This article discusses the novel features introduced in version 7.3.0. △ Less

Submitted 11 July, 2024; v1 submitted 8 December, 2023; originally announced December 2023.

Comments: 10 pages, 3 figures. Herwig is available from https://herwig.hepforge.org

Report number: CERN-TH-2023-223, HERWIG-2023-01, KA-TP-28-2023, MCnet-23-19, IPPP/23/66

Hadronization and Decay of Excited Heavy Hadrons in Herwig 7

Authors: M. R. Masouminia, P. Richardson

Abstract: We revisit the hadronization and decay of excited heavy mesons and heavy baryons in Herwig 7 general-purpose event-generator, following four distinct steps: (i) Passing through the polarization of heavy hadrons at the end of parton shower through the application of heavy quark effective theory (HQET), where the emergence of a spin-flavour symmetry allows for the determination of the polarizations… ▽ More We revisit the hadronization and decay of excited heavy mesons and heavy baryons in Herwig 7 general-purpose event-generator, following four distinct steps: (i) Passing through the polarization of heavy hadrons at the end of parton shower through the application of heavy quark effective theory (HQET), where the emergence of a spin-flavour symmetry allows for the determination of the polarizations of the excited heavy mesons and heavy baryons from the helicity states of the light and heavy quarks. (ii) Improving the strong and radiative decay modes of the excited heavy mesons, where in the absence of conclusive experimental data on many of the decays, one needs to rely on HQET symmetries to determine the favoured decay modes, widths and branching ratios. (iii) Re-examination of the production rates of heavy hadrons using all available experimental data sources and (iv) performing a general tune for Herwig's free parameters to reflect the implemented changes. We compare our predictions against existing experimental data in the presence/absence of the newly implemented updates. These improvements will be available with Herwig-7.3.0 public release. △ Less

Submitted 3 August, 2024; v1 submitted 5 December, 2023; originally announced December 2023.

Comments: 24 pages, 6 plots and 13 tables

Report number: IPPP/23/52

Journal ref: JHEP 07 (2024) 278

UFO 2.0 -- The Universal Feynman Output format

Authors: Luc Darmé, Céline Degrande, Claude Duhr, Benjamin Fuks, Mark Goodsell, Gudrun Heinrich, Valentin Hirschi, Stefan Höche, Marius Höfer, Joshua Isaacson, Olivier Mattelaer, Thorsten Ohl, Davide Pagani, Jürgen Reuter, Peter Richardson, Steffen Schumann, Hua-Sheng Shao, Frank Siegert, Marco Zaro

Abstract: We present an update of the Universal FeynRules Output model format, commonly known as the UFO format, that is used by several automated matrix-element generators and high-energy physics software. We detail different features that have been proposed as extensions of the initial format during the last ten years, and collect them in the current second version of the model format that we coin the Uni… ▽ More We present an update of the Universal FeynRules Output model format, commonly known as the UFO format, that is used by several automated matrix-element generators and high-energy physics software. We detail different features that have been proposed as extensions of the initial format during the last ten years, and collect them in the current second version of the model format that we coin the Universal Feynman Output format. Following the initial philosophy of the UFO, they consist of flexible and modular additions to address particle decays, custom propagators, form factors, the renormalisation group running of parameters and masses, and higher-order quantum corrections. △ Less

Submitted 13 July, 2023; v1 submitted 19 April, 2023; originally announced April 2023.

Comments: 28 pages; version accepted by EPJC

Report number: BONN-TH-2023-03, DESY-23-051, FERMILAB-PUB-23-138-T, KA-TP-06-2023, MCNET-23-06, P3H-23-023, TIF-UNIMI-2023-11

Journal ref: Eur.Phys.J.C 83 (2023) 631

Synthetic control of structure and conduction properties in Na-Y-Zr-Cl solid electrolytes

Authors: Elias Sebti, Ji Qi, Peter M. Richardson, Phillip Ridley, Erik A. Wu, Swastika Banerjee, Raynald Giovine, Ashley Cronk, So-Yeon Ham, Ying Shirley Meng, Shyue Ping Ong, Raphaële J. Clément

Abstract: In the development of low cost, sustainable, and energy-dense batteries, chloride-based compounds are promising catholyte materials for solid-state batteries owing to their high Na-ion conductivities and oxidative stabilities. The ability to further improve Na-ion conduction, however, requires an understanding of the impact of long-range and local structural features on transport in these systems.… ▽ More In the development of low cost, sustainable, and energy-dense batteries, chloride-based compounds are promising catholyte materials for solid-state batteries owing to their high Na-ion conductivities and oxidative stabilities. The ability to further improve Na-ion conduction, however, requires an understanding of the impact of long-range and local structural features on transport in these systems. In this study, we leverage different synthesis methods to control polymorphism and cation disorder in Na-Y-Zr-Cl solid electrolytes and interrogate the impact on Na-ion conduction. We demonstrate the existence of a more conductive P2$_1$/n polymorph of Na$_2$ZrCl$_6$ formed upon ball milling. In Na$_3$YCl$_6$, the R$\bar{3}$ polymorph is shown to be more conductive than its P2$_1$/n counterpart owing to the presence of intrinsic vacancies and disorder on the Y sublattice. Transition metal ordering in the Na$_{2.25}$Y$_{0.25}$Zr$_{0.75}$Cl$_6$ composition strongly impacts Na-ion transport, where a greater mixing of Y$^{3+}$ and Zr$^{4+}$ on the transition metal sublattice facilitates ion migration through partial activation of Cl rotations at relevant temperatures. Overall, Na-ion transport sensitively depends on the phases and transition metal distributions stabilized during synthesis. These results are likely generalizable to other halide compositions and indicate that achieving control over the synthetic protocol and resultant structure is key in the pursuit of improved catholytes for high voltage solid-state sodium-ion batteries. △ Less

Submitted 16 August, 2022; originally announced August 2022.

Simultaneous recovery of attenuation and source density in SPECT

Authors: Sean Holman, Philip Richardson

Abstract: We show that under a certain non-cancellation condition the attenuated Radon transform uniquely determines piecewise constant attenuation $a$ and piecewise $C^2$ source density $f$ with jumps over real analytic boundaries possibly having corners. We also look at numerical examples in which the non-cancellation condition fails and show that unique reconstruction of multi-bang $a$ and $f$ is still a… ▽ More We show that under a certain non-cancellation condition the attenuated Radon transform uniquely determines piecewise constant attenuation $a$ and piecewise $C^2$ source density $f$ with jumps over real analytic boundaries possibly having corners. We also look at numerical examples in which the non-cancellation condition fails and show that unique reconstruction of multi-bang $a$ and $f$ is still appears to be possible although not yet explained by theoretical results. △ Less

Submitted 21 June, 2022; originally announced June 2022.

Comments: 28 pages, 6 figures

Event Generators for High-Energy Physics Experiments

Authors: J. M. Campbell, M. Diefenthaler, T. J. Hobbs, S. Höche, J. Isaacson, F. Kling, S. Mrenna, J. Reuter, S. Alioli, J. R. Andersen, C. Andreopoulos, A. M. Ankowski, E. C. Aschenauer, A. Ashkenazi, M. D. Baker, J. L. Barrow, M. van Beekveld, G. Bewick, S. Bhattacharya, N. Bhuiyan, C. Bierlich, E. Bothmann, P. Bredt, A. Broggio, A. Buckley , et al. (187 additional authors not shown)

Abstract: We provide an overview of the status of Monte-Carlo event generators for high-energy particle physics. Guided by the experimental needs and requirements, we highlight areas of active development, and opportunities for future improvements. Particular emphasis is given to physics models and algorithms that are employed across a variety of experiments. These common themes in event generator developme… ▽ More We provide an overview of the status of Monte-Carlo event generators for high-energy particle physics. Guided by the experimental needs and requirements, we highlight areas of active development, and opportunities for future improvements. Particular emphasis is given to physics models and algorithms that are employed across a variety of experiments. These common themes in event generator development lead to a more comprehensive understanding of physics at the highest energies and intensities, and allow models to be tested against a wealth of data that have been accumulated over the past decades. A cohesive approach to event generator development will allow these models to be further improved and systematic uncertainties to be reduced, directly contributing to future experimental success. Event generators are part of a much larger ecosystem of computational tools. They typically involve a number of unknown model parameters that must be tuned to experimental data, while maintaining the integrity of the underlying physics models. Making both these data, and the analyses with which they have been obtained accessible to future users is an essential aspect of open science and data preservation. It ensures the consistency of physics models across a variety of experiments. △ Less

Submitted 26 February, 2025; v1 submitted 21 March, 2022; originally announced March 2022.

Comments: 164 pages, 10 figures, contribution to Snowmass 2021

Report number: CP3-22-12, DESY-22-042, FERMILAB-PUB-22-116-SCD-T, IPPP/21/51, JLAB-PHY-22-3576, KA-TP-04-2022, LA-UR-22-22126, LU-TP-22-12, MCNET-22-04, OUTP-22-03P, P3H-22-024, PITT-PACC 2207, UCI-TR-2022-02

Journal ref: SciPost Phys. 16 (2024) 5, 130

Future prospects for parton showers

Authors: Neda Darvishi, Joshua Isaacson M. R. Masouminia, Zoltan Nagy, Peter Richardson, Davison E. Soper

Abstract: In this brief Snowmass White Paper for the Theory Frontier, we argue that there have been important recent developments in the algorithms used to generate a simulated parton shower and that further progress can be achieved in the coming decade. A much more detailed exposition can be found in a corresponding White Paper of the Energy Frontier. In this brief Snowmass White Paper for the Theory Frontier, we argue that there have been important recent developments in the algorithms used to generate a simulated parton shower and that further progress can be achieved in the coming decade. A much more detailed exposition can be found in a corresponding White Paper of the Energy Frontier. △ Less

Submitted 7 April, 2022; v1 submitted 13 March, 2022; originally announced March 2022.

Comments: Contribution to Snowmass 2021. Revised version has a revised author list, slightly revised text, and a few added references

The Forward Physics Facility at the High-Luminosity LHC

Authors: Jonathan L. Feng, Felix Kling, Mary Hall Reno, Juan Rojo, Dennis Soldin, Luis A. Anchordoqui, Jamie Boyd, Ahmed Ismail, Lucian Harland-Lang, Kevin J. Kelly, Vishvas Pandey, Sebastian Trojanowski, Yu-Dai Tsai, Jean-Marco Alameddine, Takeshi Araki, Akitaka Ariga, Tomoko Ariga, Kento Asai, Alessandro Bacchetta, Kincso Balazs, Alan J. Barr, Michele Battistin, Jianming Bian, Caterina Bertone, Weidong Bai , et al. (211 additional authors not shown)

Abstract: High energy collisions at the High-Luminosity Large Hadron Collider (LHC) produce a large number of particles along the beam collision axis, outside of the acceptance of existing LHC experiments. The proposed Forward Physics Facility (FPF), to be located several hundred meters from the ATLAS interaction point and shielded by concrete and rock, will host a suite of experiments to probe Standard Mod… ▽ More High energy collisions at the High-Luminosity Large Hadron Collider (LHC) produce a large number of particles along the beam collision axis, outside of the acceptance of existing LHC experiments. The proposed Forward Physics Facility (FPF), to be located several hundred meters from the ATLAS interaction point and shielded by concrete and rock, will host a suite of experiments to probe Standard Model (SM) processes and search for physics beyond the Standard Model (BSM). In this report, we review the status of the civil engineering plans and the experiments to explore the diverse physics signals that can be uniquely probed in the forward region. FPF experiments will be sensitive to a broad range of BSM physics through searches for new particle scattering or decay signatures and deviations from SM expectations in high statistics analyses with TeV neutrinos in this low-background environment. High statistics neutrino detection will also provide valuable data for fundamental topics in perturbative and non-perturbative QCD and in weak interactions. Experiments at the FPF will enable synergies between forward particle production at the LHC and astroparticle physics to be exploited. We report here on these physics topics, on infrastructure, detector, and simulation studies, and on future directions to realize the FPF's physics potential. △ Less

Submitted 9 March, 2022; originally announced March 2022.

Comments: 429 pages, contribution to Snowmass 2021

Report number: UCI-TR-2022-01, CERN-PBC-Notes-2022-001, FERMILAB-PUB-22-094-ND-SCD-T, INT-PUB-22-006, BONN-TH-2022-04

Stacking Faults Assist Lithium-Ion Conduction in a Halide-Based Superionic Conductor

Authors: Elias Sebti, Hayden A. Evans, Hengning Chen, Peter M. Richardson, Kelly M. White, Raynald Giovine, Krishna Prasad Koirala, Yaobin Xu, Eliovardo Gonzalez-Correa, Chongmin Wang, Craig M. Brown, Anthony K. Cheetham, Pieremanuele Canepa, Raphaële J. Clément

Abstract: In the pursuit of urgently-needed, energy dense solid-state batteries for electric vehicle and portable electronics applications, halide solid electrolytes offer a promising path forward with exceptional compatibility against high-voltage oxide electrodes, tunable ionic conductivities, and facile processing. For this family of compounds, synthesis protocols strongly affect cation site disorder and… ▽ More In the pursuit of urgently-needed, energy dense solid-state batteries for electric vehicle and portable electronics applications, halide solid electrolytes offer a promising path forward with exceptional compatibility against high-voltage oxide electrodes, tunable ionic conductivities, and facile processing. For this family of compounds, synthesis protocols strongly affect cation site disorder and modulate Li+ mobility. In this work, we reveal the presence of a high concentration of stacking faults in the superionic conductor Li3YCl6 and demonstrate a method of controlling its Li+ conductivity by tuning the defect concentration with synthesis and heat treatments at select temperatures. Leveraging complementary insights from variable temperature synchrotron X-ray diffraction, neutron diffraction, cryogenic transmission electron microscopy, solid-state nuclear magnetic resonance, density functional theory, and electrochemical impedance spectroscopy, we identify the nature of planar defects and the role of nonstoichiometry in lowering Li+ migration barriers and increasing Li site connectivity in mechanochemically-synthesized Li3YCl6. We harness paramagnetic relaxation enhancement to enable 89Y solid-state NMR, and directly contrast the Y cation site disorder resulting from different preparation methods, demonstrating a potent tool for other researchers studying Y-containing compositions. With heat treatments at temperatures as low as 333 K (60°C), we decrease the concentration of planar defects, demonstrating a simple method for tuning the Li+ conductivity. Findings from this work are expected to be generalizable to other halide solid electrolyte candidates and provide an improved understanding of defect-enabled Li+ conduction in this class of Li-ion conductors. △ Less

Submitted 1 March, 2022; originally announced March 2022.

Implementation of Angularly Ordered Electroweak Parton Shower in Herwig 7

Authors: M. R. Masouminia, P. Richardson

Abstract: We discuss the necessary steps for implementing an angularly ordered (AO) electroweak (EW) parton shower in Herwig 7 multi-purpose event generator. This includes calculating the helicity-dependent quasi-collinear EW branching functions that correspond to the full range of final-state EW parton shower, in addition to the initial-state EW gauge vector boson radiations. The results are successfully e… ▽ More We discuss the necessary steps for implementing an angularly ordered (AO) electroweak (EW) parton shower in Herwig 7 multi-purpose event generator. This includes calculating the helicity-dependent quasi-collinear EW branching functions that correspond to the full range of final-state EW parton shower, in addition to the initial-state EW gauge vector boson radiations. The results are successfully embedded in the AO Herwig 7 shower algorithm and have undergone a set of comprehensive and conclusive performance tests. Furthermore, we have used this EW parton shower algorithm, alongside the existing $QCD+QED$ AO shower, to predict the angular distributions of $W^{\pm}$ bosons in LHC events with high transverse momentum jets. These results are compared against the explicitly generated underlying events as well as the existing ATLAS data to show the effectiveness of the newly implemented $QCD+QED+EW$ AO parton shower scheme. △ Less

Submitted 24 August, 2021; originally announced August 2021.

Comments: 26 pages, 15 figures and 4 tables

Report number: IPPP/21/21

Journal ref: JHEP 04 (2022) 112

Initial State Radiation in the Herwig 7 Angular-Ordered Parton Shower

Authors: Gavin Bewick, Silvia Ferrario Ravasio, Peter Richardson, Michael H. Seymour

Abstract: We study the simulation of initial-state radiation in angular-ordered parton showers in order to investigate how different interpretations of the ordering variable affect the logarithmic accuracy of such showers. This also enables us to implement a recoil scheme which is consistent between final-state and initial-state radiation. We present optimal values of the strong coupling and intrinsic trans… ▽ More We study the simulation of initial-state radiation in angular-ordered parton showers in order to investigate how different interpretations of the ordering variable affect the logarithmic accuracy of such showers. This also enables us to implement a recoil scheme which is consistent between final-state and initial-state radiation. We present optimal values of the strong coupling and intrinsic transverse momentum to be used in each version of the parton shower, tuned using $Z^0$-boson production at the LHC at 7 TeV. With these tuned showers, we perform a phenomenological study of the Drell-Yan process at several centre-of-mass energies. △ Less

Submitted 14 December, 2021; v1 submitted 8 July, 2021; originally announced July 2021.

Comments: 26 pages, 7 figures, 2 tables

Report number: CERN-TH-2021-103, OUTP-21-18P, MCnet-21-13, IPPP/21/05

Multi-domain Clinical Natural Language Processing with MedCAT: the Medical Concept Annotation Toolkit

Authors: Zeljko Kraljevic, Thomas Searle, Anthony Shek, Lukasz Roguski, Kawsar Noor, Daniel Bean, Aurelie Mascio, Leilei Zhu, Amos A Folarin, Angus Roberts, Rebecca Bendayan, Mark P Richardson, Robert Stewart, Anoop D Shah, Wai Keong Wong, Zina Ibrahim, James T Teo, Richard JB Dobson

Abstract: Electronic health records (EHR) contain large volumes of unstructured text, requiring the application of Information Extraction (IE) technologies to enable clinical analysis. We present the open-source Medical Concept Annotation Toolkit (MedCAT) that provides: a) a novel self-supervised machine learning algorithm for extracting concepts using any concept vocabulary including UMLS/SNOMED-CT; b) a f… ▽ More Electronic health records (EHR) contain large volumes of unstructured text, requiring the application of Information Extraction (IE) technologies to enable clinical analysis. We present the open-source Medical Concept Annotation Toolkit (MedCAT) that provides: a) a novel self-supervised machine learning algorithm for extracting concepts using any concept vocabulary including UMLS/SNOMED-CT; b) a feature-rich annotation interface for customising and training IE models; and c) integrations to the broader CogStack ecosystem for vendor-agnostic health system deployment. We show improved performance in extracting UMLS concepts from open datasets (F1:0.448-0.738 vs 0.429-0.650). Further real-world validation demonstrates SNOMED-CT extraction at 3 large London hospitals with self-supervised training over ~8.8B words from ~17M clinical records and further fine-tuning with ~6K clinician annotated examples. We show strong transferability (F1 > 0.94) between hospitals, datasets, and concept types indicating cross-domain EHR-agnostic utility for accelerated clinical and research use cases. △ Less

Submitted 25 March, 2021; v1 submitted 2 October, 2020; originally announced October 2020.

Comments: Preprint: 27 Pages, 3 Figures

Defect behavior and radiation tolerance of MAB phases (MoAlB and Fe2AlB2) with comparison to MAX phases

Authors: Hongliang Zhang, JunYoung Kim, Ranran Su, Peter Richardson, Jianqi Xi, Erich Kisi, John O'Connor, Liqun Shi, Izabela Szlufarska

Abstract: MAB phases are a new class of layered ternary materials that have already shown a number of outstanding properties. Here, we investigate defect evolution and radiation tolerance of two MAB phases, MoAlB and Fe2AlB2, using a combination of experimental characterization and first-principles calculations. We find that Fe2AlB2 is more tolerant to radiation-induced amorphization than MoAlB, both at 150… ▽ More MAB phases are a new class of layered ternary materials that have already shown a number of outstanding properties. Here, we investigate defect evolution and radiation tolerance of two MAB phases, MoAlB and Fe2AlB2, using a combination of experimental characterization and first-principles calculations. We find that Fe2AlB2 is more tolerant to radiation-induced amorphization than MoAlB, both at 150 °C and at 300 °C. The results can be explained by the fact that the Mo Frenkel pair is unstable in MoAlB and as a result, irradiated MoAlB is expected to have a significant concentration of MoAl antisites, which are difficult to anneal even at 300 °C. We find that the tolerance to radiation-induced amorphization of MAB phases is lower than in MAX phases, but it is comparable to that of SiC. However, MAB phases do not show radiation-induced cracking which is observed in MAX phases under the same irradiation conditions. This study suggests that MAB phases might be a promising class of materials for applications that involve radiation. △ Less

Submitted 12 August, 2020; originally announced August 2020.

Journal ref: Acta Materialia, 2020

Fighting seizures with seizures: diffusion and stability in neural systems

Authors: Erik D. Fagerholm, Chayanin Tangwiriyasakul, Karl J. Friston, Inês R. Violante, Steven Williams, David W. Carmichael, Suejen Perani, Federico E. Turkheimer, Rosalyn J. Moran, Robert Leech, Mark P. Richardson

Abstract: Seizure activity is a ubiquitous and pernicious pathophysiology that, in principle, should yield to mathematical treatments of (neuronal) ensemble dynamics - and therefore interventions on stochastic chaos. A seizure can be characterised as a deviation of neural activity from a stable dynamical regime, i.e. one in which signals fluctuate only within a limited range. In silico treatments of neural… ▽ More Seizure activity is a ubiquitous and pernicious pathophysiology that, in principle, should yield to mathematical treatments of (neuronal) ensemble dynamics - and therefore interventions on stochastic chaos. A seizure can be characterised as a deviation of neural activity from a stable dynamical regime, i.e. one in which signals fluctuate only within a limited range. In silico treatments of neural activity are an important tool for understanding how the brain can achieve stability, as well as how pathology can lead to seizures and potential strategies for mitigating instabilities, e.g. via external stimulation. Here, we demonstrate that the (neuronal) state equation used in Dynamic Causal Modelling generalises to a Fokker-Planck formalism when propagation of neuronal activity along structural connections is considered. Using the Jacobian of this generalised state equation, we show that an initially unstable system can be rendered stable via a reduction in diffusivity (i.e., connectivity that disperses neuronal fluctuations). We show, for neural systems prone to epileptic seizures, that such a reduction can be achieved via external stimulation. Specifically, we show that this stimulation should be applied in such a way as to temporarily mirror epileptic activity in the areas adjoining an affected brain region - thus 'fighting seizures with seizures'. We offer proof of principle using simulations based on functional neuroimaging data collected from patients with idiopathic generalised epilepsy, in which we successfully suppress pathological activity in a distinct sub-network. Our hope is that this technique can form the basis for real-time monitoring and intervention devices that are capable of suppressing or even preventing seizures in a non-invasive manner. △ Less

Submitted 2 May, 2020; originally announced May 2020.

Estimating required 'lockdown' cycles before immunity to SARS-CoV-2: Model-based analyses of susceptible population sizes, 'S0', in seven European countries including the UK and Ireland

Authors: Rosalyn J. Moran, Erik D. Fagerholm, Maell Cullen, Jean Daunizeau, Mark P. Richardson, Steven Williams, Federico Turkheimer, Rob Leech, Karl J. Friston

Abstract: We used Bayesian model inversion to estimate epidemic parameters from the reported case and death rates from seven countries using data from late January 2020 to April 5th 2020. Two distinct generative model types were employed: first a continuous time dynamical-systems implementation of a Susceptible-Exposed-Infectious-Recovered (SEIR) model and second: a partially observable Markov Decision Proc… ▽ More We used Bayesian model inversion to estimate epidemic parameters from the reported case and death rates from seven countries using data from late January 2020 to April 5th 2020. Two distinct generative model types were employed: first a continuous time dynamical-systems implementation of a Susceptible-Exposed-Infectious-Recovered (SEIR) model and second: a partially observable Markov Decision Process (MDP) or hidden Markov model (HMM) implementation of an SEIR model. Both models parameterise the size of the initial susceptible population (S0), as well as epidemic parameters. Parameter estimation (data fitting) was performed using a standard Bayesian scheme (variational Laplace) designed to allow for latent unobservable states and uncertainty in model parameters. Both models recapitulated the dynamics of transmissions and disease as given by case and death rates. The peaks of the current waves were predicted to be in the past for four countries (Italy, Spain, Germany and Switzerland) and to emerge in 0.5-2 weeks in Ireland and 1-3 weeks in the UK. For France one model estimated the peak within the past week and the other in the future in two weeks. Crucially, Maximum a posteriori (MAP) estimates of S0 for each country indicated effective population sizes of below 20% (of total population size), under both the continuous time and HMM models. With a Bayesian weighted average across all seven countries and both models, we estimated that 6.4% of the total population would be immune. From the two models the maximum percentage of the effective population was estimated at 19.6% of the total population for the UK, 16.7% for Ireland, 11.4% for Italy, 12.8% for Spain, 18.8% for France, 4.7% for Germany and 12.9% for Switzerland. Our results indicate that after the current wave, a large proportion of the total population will remain without immunity. △ Less

Submitted 9 April, 2020; originally announced April 2020.

Les Houches 2019: Physics at TeV Colliders: Standard Model Working Group Report

Authors: S. Amoroso, P. Azzurri, J. Bendavid, E. Bothmann, D. Britzger, H. Brooks, A. Buckley, M. Calvetti, X. Chen, M. Chiesa, L. Cieri, V. Ciulli, J. Cruz-Martinez, A. Cueto, A. Denner, S. Dittmaier, M. Donegà, M. Dührssen-Debling, I. Fabre, S. Ferrario-Ravasio, D. de Florian, S. Forte, P. Francavilla, T. Gehrmann, A. Gehrmann-De Ridder , et al. (58 additional authors not shown)

Abstract: This Report summarizes the proceedings of the 2019 Les Houches workshop on Physics at TeV Colliders. Session 1 dealt with (I) new developments for high precision Standard Model calculations, (II) the sensitivity of parton distribution functions to the experimental inputs, (III) new developments in jet substructure techniques and a detailed examination of gluon fragmentation at the LHC, (IV) issues… ▽ More This Report summarizes the proceedings of the 2019 Les Houches workshop on Physics at TeV Colliders. Session 1 dealt with (I) new developments for high precision Standard Model calculations, (II) the sensitivity of parton distribution functions to the experimental inputs, (III) new developments in jet substructure techniques and a detailed examination of gluon fragmentation at the LHC, (IV) issues in the theoretical description of the production of Standard Model Higgs bosons and how to relate experimental measurements, and (V) Monte Carlo event generator studies relating to PDF evolution and comparisons of important processes at the LHC. △ Less

Submitted 3 March, 2020; originally announced March 2020.

Comments: Proceedings of the Standard Model Working Group of the 2019 Les Houches Workshop, Physics at TeV Colliders, Les Houches 10-28 June 2019. 226 pages

Model-assisted cohort selection with bias analysis for generating large-scale cohorts from the EHR for oncology research

Authors: Benjamin Birnbaum, Nathan Nussbaum, Katharina Seidl-Rathkopf, Monica Agrawal, Melissa Estevez, Evan Estola, Joshua Haimson, Lucy He, Peter Larson, Paul Richardson

Abstract: Objective Electronic health records (EHRs) are a promising source of data for health outcomes research in oncology. A challenge in using EHR data is that selecting cohorts of patients often requires information in unstructured parts of the record. Machine learning has been used to address this, but even high-performing algorithms may select patients in a non-random manner and bias the resulting co… ▽ More Objective Electronic health records (EHRs) are a promising source of data for health outcomes research in oncology. A challenge in using EHR data is that selecting cohorts of patients often requires information in unstructured parts of the record. Machine learning has been used to address this, but even high-performing algorithms may select patients in a non-random manner and bias the resulting cohort. To improve the efficiency of cohort selection while measuring potential bias, we introduce a technique called Model-Assisted Cohort Selection (MACS) with Bias Analysis and apply it to the selection of metastatic breast cancer (mBC) patients. Materials and Methods We trained a model on 17,263 patients using term-frequency inverse-document-frequency (TF-IDF) and logistic regression. We used a test set of 17,292 patients to measure algorithm performance and perform Bias Analysis. We compared the cohort generated by MACS to the cohort that would have been generated without MACS as reference standard, first by comparing distributions of an extensive set of clinical and demographic variables and then by comparing the results of two analyses addressing existing example research questions. Results Our algorithm had an area under the curve (AUC) of 0.976, a sensitivity of 96.0%, and an abstraction efficiency gain of 77.9%. During Bias Analysis, we found no large differences in baseline characteristics and no differences in the example analyses. Conclusion MACS with bias analysis can significantly improve the efficiency of cohort selection on EHR data while instilling confidence that outcomes research performed on the resulting cohort will not be biased. △ Less

Submitted 13 January, 2020; originally announced January 2020.

Comments: Word count: Abstract, 254; text, 3934 Keywords: electronic health record; machine learning; cancer; real-world evidence

Emission tomography with a multi-bang assumption on attenuation

Authors: Sean Holman, Philip Richardson

Abstract: We consider the problem of joint reconstruction of both attenuation $a$ and source density $f$ in emission tomography in two dimensions. This is sometimes called the Single Photon Emission Computed Tomography (SPECT) identification problem, or referred to as attenuation correction in SPECT. Assuming that $a$ takes only finitely many values and $f \in C_c^1(\mathbb{R}^2)$ we are able to characteris… ▽ More We consider the problem of joint reconstruction of both attenuation $a$ and source density $f$ in emission tomography in two dimensions. This is sometimes called the Single Photon Emission Computed Tomography (SPECT) identification problem, or referred to as attenuation correction in SPECT. Assuming that $a$ takes only finitely many values and $f \in C_c^1(\mathbb{R}^2)$ we are able to characterise singularities appearing in the Attenuated Radon Transform $R_a f$, which models emission tomography data. Using this characterisation we prove that both $a$ and $f$ can be determined in some circumstances. We also propose a numerical algorithm to jointly compute $a$ and $f$ from $R_af$ based on a weakly convex regularizer when $a$ only takes values from a known finite list, and show that this algorithm performs well on some synthetic examples. △ Less

Submitted 13 January, 2020; originally announced January 2020.

Comments: 23 pages, 7 figures

MSC Class: 45Q05

Herwig 7.2 Release Note

Authors: Johannes Bellm, Gavin Bewick, Silvia Ferrario Ravasio, Stefan Gieseke, David Grellscheid, Patrick Kirchgaesser, Mohammad R. Masouminia, Graeme Nail, Andreas Papaefstathiou, Simon Platzer, Michael Rauch, Christian Reuschle, Peter Richardson, Michael H. Seymour, Andrzej Siodmok, Stephen Webster

Abstract: A new release of the Monte Carlo event generator Herwig (version 7.2) is now available. This version introduces a number of improvements, notably: improvements to the simulation of multiple-parton interactions, including diffractive processes; a new model for baryonic colour re-connection; spin correlations in both the dipole and angular-ordered parton showers; improvements to strangeness producti… ▽ More A new release of the Monte Carlo event generator Herwig (version 7.2) is now available. This version introduces a number of improvements, notably: improvements to the simulation of multiple-parton interactions, including diffractive processes; a new model for baryonic colour re-connection; spin correlations in both the dipole and angular-ordered parton showers; improvements to strangeness production; an improved choice of evolution variable in the angular-ordered parton shower; support for generic Lorentz structures in BSM models. △ Less

Submitted 12 December, 2019; originally announced December 2019.

Comments: 7 pages, 5 figures. Herwig is available from https://herwig.hepforge.org. arXiv admin note: text overlap with arXiv:1705.06919

Report number: MAN/HEP/2019/011, CERN-TH-2019-213, IFJPAN-IV-2019-18, HERWIG-2019-02, UWTHPH-19-36, KA-TP-24-2019, LU-TP 19-57, MCnet-19-28, IPPP/19/91

Robust Independent Validation of Experiment and Theory: Rivet version 3

Authors: C. Bierlich, A. Buckley, J. M. Butterworth, C. H. Christensen, L. Corpe, D. Grellscheid, J. F. Grosse-Oetringhaus, C. Gutschow, P. Karczmarczyk, J. Klein, L. Lonnblad, C. S. Pollard, P. Richardson, H. Schulz, F. Siegert

Abstract: First released in 2010, the Rivet library forms an important repository for analysis code, facilitating comparisons between measurements of the final state in particle collisions and theoretical calculations of those final states. We give an overview of Rivet's current design and implementation, its uptake for analysis preservation and physics results, and summarise recent developments including p… ▽ More First released in 2010, the Rivet library forms an important repository for analysis code, facilitating comparisons between measurements of the final state in particle collisions and theoretical calculations of those final states. We give an overview of Rivet's current design and implementation, its uptake for analysis preservation and physics results, and summarise recent developments including propagation of MC systematic-uncertainty weights, heavy-ion and $ep$ physics, and systems for detector emulation. In addition, we provide a short user guide that supplements and updates the Rivet user manual. △ Less

Submitted 6 February, 2020; v1 submitted 11 December, 2019; originally announced December 2019.

Report number: MCnet-19-26

Journal ref: SciPost Phys. 8, 026 (2020)

Hadronic Footprint of GeV-Mass Dark Matter

Authors: Tilman Plehn, Peter Reimitz, Peter Richardson

Abstract: GeV-scale dark matter is an increasingly attractive target for direct detection, indirect detection, and collider searches. Its annihilation into hadronic final states produces a challenging zoo of light hadronic resonances. We update Herwig7 to study the photon and positron spectra from annihilation through a vector mediator. It covers dark matter masses between 250 MeV and 5 GeV and includes an… ▽ More GeV-scale dark matter is an increasingly attractive target for direct detection, indirect detection, and collider searches. Its annihilation into hadronic final states produces a challenging zoo of light hadronic resonances. We update Herwig7 to study the photon and positron spectra from annihilation through a vector mediator. It covers dark matter masses between 250 MeV and 5 GeV and includes an error estimate. △ Less

Submitted 5 June, 2020; v1 submitted 25 November, 2019; originally announced November 2019.

Comments: 33 pages, 8 figures

Report number: CERN-TH-2019-202, IPPP/19/87

Journal ref: SciPost Phys. 8, 092 (2020)

Logarithmic Accuracy of Angular-Ordered Parton Showers

Authors: Gavin Bewick, Silvia Ferrario Ravasio, Peter Richardson, Michael H. Seymour

Abstract: We study the logarithmic accuracy of angular-ordered parton showers by considering the singular limits of multiple emission matrix elements. This allows us to consider different choices for the evolution variable and propose a new choice which has both the correct logarithmic behaviour and improved performance away from the singular regions. In particular the description of $e^+e^-$ event shapes i… ▽ More We study the logarithmic accuracy of angular-ordered parton showers by considering the singular limits of multiple emission matrix elements. This allows us to consider different choices for the evolution variable and propose a new choice which has both the correct logarithmic behaviour and improved performance away from the singular regions. In particular the description of $e^+e^-$ event shapes in the non-logarithmic region is significantly improved. △ Less

Submitted 26 March, 2020; v1 submitted 26 April, 2019; originally announced April 2019.

Report number: MAN/HEP/2019/003, CERN-TH-2019-047, MCnet-19-08, IPPP/19/30

Monte Carlo event generators for high energy particle physics event simulation

Authors: Andy Buckley, Frank Krauss, Simon Plätzer, Michael Seymour, Simone Alioli, Jeppe Andersen, Johannes Bellm, Jon Butterworth, Mrinal Dasgupta, Claude Duhr, Stefano Frixione, Stefan Gieseke, Keith Hamilton, Gavin Hesketh, Stefan Hoeche, Hannes Jung, Wolfgang Kilian, Leif Lönnblad, Fabio Maltoni, Michelangelo Mangano, Stephen Mrenna, Zoltán Nagy, Paolo Nason, Emily Nurse, Thorsten Ohl , et al. (18 additional authors not shown)

Abstract: Monte Carlo event generators (MCEGs) are the indispensable workhorses of particle physics, bridging the gap between theoretical ideas and first-principles calculations on the one hand, and the complex detector signatures and data of the experimental community on the other hand. All collider physics experiments are dependent on simulated events by MCEG codes such as Herwig, Pythia, Sherpa, POWHEG,… ▽ More Monte Carlo event generators (MCEGs) are the indispensable workhorses of particle physics, bridging the gap between theoretical ideas and first-principles calculations on the one hand, and the complex detector signatures and data of the experimental community on the other hand. All collider physics experiments are dependent on simulated events by MCEG codes such as Herwig, Pythia, Sherpa, POWHEG, and MG5_aMC@NLO to design and tune their detectors and analysis strategies. The development of MCEGs is overwhelmingly driven by a vibrant community of academics at European Universities, who also train the next generations of particle phenomenologists. The new challenges posed by possible future collider-based experiments and the fact that the first analyses at Run II of the LHC are now frequently limited by theory uncertainties urge the community to invest into further theoretical and technical improvements of these essential tools. In this short contribution to the European Strategy Update, we briefly review the state of the art, and the further developments that will be needed to meet the challenges of the next generation. △ Less

Submitted 5 February, 2019; originally announced February 2019.

Comments: Monte Carlo Community input to European Strategy Update

Report number: MCnet-19-02

Parton Shower and Matching Uncertainties in Top Quark Pair Production with Herwig 7

Authors: Kyle Cormier, Simon Plätzer, Christian Reuschle, Peter Richardson, Stephen Webster

Abstract: We evaluate the theoretical uncertainties in next-to-leading order plus parton shower predictions for top quark pair production and decay in hadronic collisions. Our work is carried out using the Herwig 7 event generator and presents an in-depth study of variations in matching schemes with two systematically different shower algorithms, the traditional angular-ordered and alternative dipole shower… ▽ More We evaluate the theoretical uncertainties in next-to-leading order plus parton shower predictions for top quark pair production and decay in hadronic collisions. Our work is carried out using the Herwig 7 event generator and presents an in-depth study of variations in matching schemes with two systematically different shower algorithms, the traditional angular-ordered and alternative dipole shower. We also present all of the required extensions of the Herwig dipole shower algorithm to properly take into account quark mass effects, as well as its ability to perform top quark decays. The predictions are compared at parton level as well as to LHC data, including in the boosted regime. We find that the regions where predictions with a non-top-quark-specific tune differ drastically from data are plagued by large uncertainties which are consistent between our two shower and matching algorithms. △ Less

Submitted 15 October, 2018; originally announced October 2018.

Comments: 38 pages, 19 figures

Report number: CERN-TH-2018-219, HERWIG-2018-03, IPPP/18/91, LU-TP 18-33, MCNET-18-28, UWTHPH-2018-22

Spin Correlations in Parton Shower Simulations

Authors: Peter Richardson, Stephen Webster

Abstract: Spin correlations are an important, but often neglected, effect in modern Monte Carlo event generators. We show that they can be fully incorporated in Herwig 7 using the algorithm originally proposed by Collins and Knowles in all stages of the event generation process and between the different stages of the event generation. In this paper we present the final missing ingredient, correlations in bo… ▽ More Spin correlations are an important, but often neglected, effect in modern Monte Carlo event generators. We show that they can be fully incorporated in Herwig 7 using the algorithm originally proposed by Collins and Knowles in all stages of the event generation process and between the different stages of the event generation. In this paper we present the final missing ingredient, correlations in both the angular-ordered and dipole shower algorithms and between the parton shower and hard production and decay processes. △ Less

Submitted 5 July, 2018; originally announced July 2018.

Comments: 13 pages, 12 figures, 3 tables

Report number: CERN-TH-2018-154, IPPP/18/55, MCnet-18-12

Les Houches 2017: Physics at TeV Colliders New Physics Working Group Report

Authors: G. Brooijmans, M. Dolan, S. Gori, F. Maltoni, M. McCullough, P. Musella, L. Perrozzi, P. Richardson, F. Riva, A. Angelescu, S. Banerjee, D. Barducci, G. Bélanger, B. Bhattacherjee, M. Borsato, A. Buckley, J. M. Butterworth, G. Cacciapaglia, H. Cai, A. Carvalho, A. Chakraborty, G. Cottin, A. Deandrea, J. de Blas, N. Desai , et al. (58 additional authors not shown)

Abstract: We present the activities of the `New Physics' working group for the `Physics at TeV Colliders' workshop (Les Houches, France, 5--23 June, 2017). Our report includes new physics studies connected with the Higgs boson and its properties, direct search strategies, reinterpretation of the LHC results in the building of viable models and new computational tool developments. We present the activities of the `New Physics' working group for the `Physics at TeV Colliders' workshop (Les Houches, France, 5--23 June, 2017). Our report includes new physics studies connected with the Higgs boson and its properties, direct search strategies, reinterpretation of the LHC results in the building of viable models and new computational tool developments. △ Less

Submitted 27 March, 2018; originally announced March 2018.

Comments: Les Houches 2017 proceedings, 224 pages, many figures

Les Houches 2017: Physics at TeV Colliders Standard Model Working Group Report

Authors: J. Bendavid, F. Caola, V. Ciulli, R. Harlander, G. Heinrich, J. Huston, S. Kallweit, S. Prestel, E. Re, K. Tackmann, J. Thaler, K. Theofilatos, J. R. Andersen, J. Bellm, N. Berger, D. Bhatia, B. Biedermann, S. Bräuer, D. Britzger, A. G. Buckley, R. Camacho, G. Chachamis, S. Chatterjee, X. Chen, M. Chiesa , et al. (80 additional authors not shown)

Abstract: This Report summarizes the proceedings of the 2017 Les Houches workshop on Physics at TeV Colliders. Session 1 dealt with (I) new developments relevant for high precision Standard Model calculations, (II) theoretical uncertainties and dataset dependence of parton distribution functions, (III) new developments in jet substructure techniques, (IV) issues in the theoretical description of the product… ▽ More This Report summarizes the proceedings of the 2017 Les Houches workshop on Physics at TeV Colliders. Session 1 dealt with (I) new developments relevant for high precision Standard Model calculations, (II) theoretical uncertainties and dataset dependence of parton distribution functions, (III) new developments in jet substructure techniques, (IV) issues in the theoretical description of the production of Standard Model Higgs bosons and how to relate experimental measurements, (V) phenomenological studies essential for comparing LHC data from Run II with theoretical predictions and projections for future measurements, and (VI) new developments in Monte Carlo event generators. △ Less

Submitted 21 March, 2018; originally announced March 2018.

Comments: Proceedings of the Standard Model Working Group of the 2017 Les Houches Workshop, Physics at TeV Colliders, Les Houches 5-23 June 2017. 314 pages

Report number: UWTHPH-2018-5

Top Quark Production and Decay in Herwig 7.1

Authors: Johannes Bellm, Kyle Cormier, Stefan Gieseke, Simon Plätzer, Christian Reuschle, Peter Richardson, Stephen Webster

Abstract: A summary of recent developments in the simulation of top quark production and decay in the Herwig Monte Carlo event generator. A summary of recent developments in the simulation of top quark production and decay in the Herwig Monte Carlo event generator. △ Less

Submitted 18 January, 2018; v1 submitted 30 November, 2017; originally announced November 2017.

Comments: Presented at 10th International Workshop on Top Quark Physics 2017 (TOP 2017), Braga, Portugal

Report number: CERN-TH-2017-253, HERWIG-2017-03, IPPP/17/93, KA-TP-41-2017, LU-TP-17-41, MCnet-17-21, UWTHPH-2017-42

Improving the Simulation of Quark and Gluon Jets with Herwig 7

Authors: Daniel Reichelt, Peter Richardson, Andrzej Siodmok

Abstract: The properties of quark and gluon jets, and the differences between them, are increasingly important at the LHC. However, Monte Carlo event generators are normally tuned to data from $e^+e^-$ collisions which are primarily sensitive to quark-initiated jets. In order to improve the description of gluon jets we make improvements to the perturbative and the non-perturbative modelling of gluon jets an… ▽ More The properties of quark and gluon jets, and the differences between them, are increasingly important at the LHC. However, Monte Carlo event generators are normally tuned to data from $e^+e^-$ collisions which are primarily sensitive to quark-initiated jets. In order to improve the description of gluon jets we make improvements to the perturbative and the non-perturbative modelling of gluon jets and include data with gluon-initiated jets in the tuning for the first time. The resultant tunes significantly improve the description of gluon jets and are now the default in Herwig 7.1. △ Less

Submitted 4 August, 2017; originally announced August 2017.

Report number: CERN-TH-2017-174, IFJPAN-IV-2017-16, MCnet-17-13

Herwig 7.1 Release Note

Authors: Johannes Bellm, Stefan Gieseke, David Grellscheid, Patrick Kirchgaeßer, Frashër Loshaj, Graeme Nail, Andreas Papaefstathiou, Simon Plätzer, Radek Podskubka, Michael Rauch, Christian Reuschle, Peter Richardson, Peter Schichtel, Michael H. Seymour, Andrzej Siódmok, Stephen Webster

Abstract: A new release of the Monte Carlo event generator Herwig (version 7.1) is now available. This version introduces a number of improvements, notably: multi-jet merging with the dipole shower at LO and NLO QCD; a new model for soft interactions and diffraction; improvements to mass effects and top decays in the dipole shower, as well as a new tune of the hadronisation parameters. A new release of the Monte Carlo event generator Herwig (version 7.1) is now available. This version introduces a number of improvements, notably: multi-jet merging with the dipole shower at LO and NLO QCD; a new model for soft interactions and diffraction; improvements to mass effects and top decays in the dipole shower, as well as a new tune of the hadronisation parameters. △ Less

Submitted 19 May, 2017; originally announced May 2017.

Comments: 7 pages, 7 figures. Herwig is available from https://herwig.hepforge.org/

Report number: CERN-PH-TH-2017-109, MAN/HEP/2017/08, UWTHPH-2017-10, IFJPAN-IV-2017-7, NIKHEF 2017-026, HERWIG-2017-02, KA-TP-19-2017, MCnet-17-08, IPPP/17/40

Parton Radiation and Fragmentation from LHC to FCC-ee

Authors: David d'Enterria, Peter Z. Skands, D. Anderle, F. Anulli, J. Aparisi, G. Bell, V. Bertone, C. Bierlich, S. Carrazza, G. Corcella, D. d'Enterria, M. Dasgupta, I. Garcia, T. Gehrmann, O. Gituliar, K. Hamacher, N. P. Hartland, A. H. Hoang, A. Hornig, S. Jadach, T. Kaufmann, S. Kluth, D. W. Kolodrubetz, A. Kusina, C. Lee , et al. (31 additional authors not shown)

Abstract: This document collects the proceedings of the "Parton Radiation and Fragmentation from LHC to FCC-ee" workshop (http://indico.cern.ch/e/ee\_jets16) held at CERN in Nov. 2016. The writeup reviews the latest theoretical and experimental developments on parton radiation and parton-hadron fragmentation studies --including analyses of LEP, B-factories, and LHC data-- with a focus on the future perspect… ▽ More This document collects the proceedings of the "Parton Radiation and Fragmentation from LHC to FCC-ee" workshop (http://indico.cern.ch/e/ee\_jets16) held at CERN in Nov. 2016. The writeup reviews the latest theoretical and experimental developments on parton radiation and parton-hadron fragmentation studies --including analyses of LEP, B-factories, and LHC data-- with a focus on the future perspectives reacheable in $e^+e^-$ measurements at the Future Circular Collider (FCC-ee), with multi-ab$^{-1}$ integrated luminosities yielding 10$^{12}$ and 10$^{8}$ jets from Z and W bosons decays as well as 10$^5$ gluon jets from Higgs boson decays. The main topics discussed are: (i) parton radiation and parton-to-hadron fragmentation functions (splitting functions at NNLO, small-$z$ NNLL resummations, global FF fits including Monte Carlo (MC) and neural-network analyses of the latest Belle/BaBar high-precision data, parton shower MC generators), (ii) jet properties (quark-gluon discrimination, $e^+e^-$ event shapes and multi-jet rates at NNLO+N$^{n}$LL, jet broadening and angularities, jet substructure at small-radius, jet charge determination, $e^+e^-$ jet reconstruction algorithms), (iii) heavy-quark jets (dead cone effect, charm-bottom separation, gluon-to-$b\bar{b}$ splitting), and (iv) non-perturbative QCD phenomena (colour reconnection, baryon and strangeness production, Bose-Einstein and Fermi-Dirac final-state correlations, colour string dynamics: spin effects, helix hadronization). △ Less

Submitted 4 February, 2017; originally announced February 2017.

Comments: 181 pages, 120 figures. Proceedings "Parton Radiation and Fragmentation from LHC to FCC-ee" Workshop (CERN, Nov. 2016), David d'Enterria, Peter Z. Skands (eds.)

Report number: CoEPP-MN-17-1

Counting fixed points and rooted closed walks of the singular map $x \mapsto x^{x^n}$ modulo powers of a prime

Authors: Joshua Holden, Pamela A. Richardson, Margaret M. Robinson

Abstract: The "self-power" map $x \mapsto x^x$ modulo $m$ and its generalized form $x \mapsto x^{x^n}$ modulo $m$ are of considerable interest for both theoretical reasons and for potential applications to cryptography. In this paper, we use $p$-adic methods, primarily $p$-adic interpolation, Hensel's lemma, and lifting singular points modulo $p$, to count fixed points and rooted closed walks of equations r… ▽ More The "self-power" map $x \mapsto x^x$ modulo $m$ and its generalized form $x \mapsto x^{x^n}$ modulo $m$ are of considerable interest for both theoretical reasons and for potential applications to cryptography. In this paper, we use $p$-adic methods, primarily $p$-adic interpolation, Hensel's lemma, and lifting singular points modulo $p$, to count fixed points and rooted closed walks of equations related to these maps when $m$ is a prime power. In particular, we introduce a new technique for lifting singular solutions of several congruences in several unknowns using the left kernel of the Jacobian matrix. △ Less

Submitted 26 May, 2020; v1 submitted 21 September, 2016; originally announced September 2016.

Comments: 18 pages. Version 2 shortens proofs, reduces redundancy, and introduces new technique for counting rooted closed walks. Version 3 updates title to agree with journal publication

MSC Class: 11D88 (Primary) 11A07; 11T71; 94A60 (Secondary)

Journal ref: p-Adic Numbers, Ultrametric Analysis and Applications, 2020, Vol. 12, No. 1, pp. 12-28

Reweighting Parton Showers

Authors: Johannes Bellm, Simon Plätzer, Peter Richardson, Andrzej Siódmok, Stephen Webster

Abstract: We report on the possibility of reweighting parton-shower Monte Carlo predictions for scale variations in the parton-shower algorithm. The method is based on a generalization of the Sudakov veto algorithm. We demonstrate the feasibility of this approach using example physical distributions. Implementations are available for both the parton-shower modules in the Herwig 7 event generator. We report on the possibility of reweighting parton-shower Monte Carlo predictions for scale variations in the parton-shower algorithm. The method is based on a generalization of the Sudakov veto algorithm. We demonstrate the feasibility of this approach using example physical distributions. Implementations are available for both the parton-shower modules in the Herwig 7 event generator. △ Less

Submitted 26 May, 2016; originally announced May 2016.

Comments: 8 pages, 5 figures

Report number: MAN/HEP/2016/09, CERN-TH-2016-124, IFJPAN-IV-2016-12, HERWIG-2016-05, MCnet-16-16, IPPP/16/48

Journal ref: Phys. Rev. D 94, 034028 (2016)

NLO efforts in Herwig++

Authors: Christian Reuschle, Johannes Bellm, Stefan Gieseke, David Grellscheid, Simon Plätzer, Michael Rauch, Peter Richardson, Peter Schichtel, Michael H. Seymour, Andrzej Siodmok, Alexandra Wilcock, Nadine Fischer, Marco A. Harrendorf, Graeme Nail, Andreas Papaefstathiou, Daniel Rauch

Abstract: With the advent and recent extension of the BLHA standard to interface Monte Carlo event generators and one-loop matrix element providers, the Herwig++ event generator has expanded its range of applicability to a multitude of underlying hard processes at NLO QCD. The new NLO development is centered around the Matchbox framework, which turns fixed NLO QCD calculations into parton shower matched cal… ▽ More With the advent and recent extension of the BLHA standard to interface Monte Carlo event generators and one-loop matrix element providers, the Herwig++ event generator has expanded its range of applicability to a multitude of underlying hard processes at NLO QCD. The new NLO development is centered around the Matchbox framework, which turns fixed NLO QCD calculations into parton shower matched calculations - to be matched to the two parton shower variants of Herwig++. Matchbox provides thereby for the automated setup of the underlying fixed NLO QCD calculations and the interface to the one-loop matrix element providers, as well as for an efficient and automated multi-channel phase space sampling, and forms the basis for the NLO capabilities of the new release of Herwig++. Along with several other new features and developments, the new release marks the end of distinguishing Herwig++ and (Fortran) HERWIG, and constitutes the first major release of version 7 of the Herwig event generator. △ Less

Submitted 15 January, 2016; originally announced January 2016.

Comments: 11 pages, 12th International Symposium on Radiative Corrections (Radcor 2015) and LoopFest XIV (Radiative Corrections for the LHC and Future Colliders), 15-19 June 2015, UCLA Department of Physics & Astronomy Los Angeles, CA, USA

Report number: HERWIG-2016-01, KA-TP-03-2016, MCnet-16-01

Herwig 7.0 / Herwig++ 3.0 Release Note

Authors: Johannes Bellm, Stefan Gieseke, David Grellscheid, Simon Plätzer, Michael Rauch, Christian Reuschle, Peter Richardson, Peter Schichtel, Michael H. Seymour, Andrzej Siódmok, Alexandra Wilcock, Nadine Fischer, Marco A. Harrendorf, Graeme Nail, Andreas Papaefstathiou, Daniel Rauch

Abstract: A major new release of the Monte Carlo event generator Herwig++ (version 3.0) is now available. This release marks the end of distinguishing Herwig++ and HERWIG development and therefore constitutes the first major release of version 7 of the Herwig event generator family. The new version features a number of significant improvements to the event simulation, including: built-in NLO hard process ca… ▽ More A major new release of the Monte Carlo event generator Herwig++ (version 3.0) is now available. This release marks the end of distinguishing Herwig++ and HERWIG development and therefore constitutes the first major release of version 7 of the Herwig event generator family. The new version features a number of significant improvements to the event simulation, including: built-in NLO hard process calculation for all Standard Model processes, with matching to both angular-ordered and dipole shower modules via both subtractive (MC@NLO-type) and multiplicative (Powheg-type) algorithms; QED radiation and spin correlations in the angular ordered shower; a consistent treatment of perturbative uncertainties within the hard process and parton showering. Several of the new features will be covered in detail in accompanying publications, and an update of the manual will follow in due course. △ Less

Submitted 3 December, 2015; originally announced December 2015.

Comments: 8 pages. Herwig is available from https://herwig.hepforge.org

Report number: CERN-PH-TH-2015-289, MAN/HEP/2015/15, IFJPAN-IV-2015-13, HERWIG-2015-01, KA-TP-18-2015, DCPT/15/142, MCnet-15-28, IPPP/15/71

Studying the sensitivity of monotop probes to compressed supersymmetric scenarios at the LHC

Authors: Benjamin Fuks, Peter Richardson, Alexandra Wilcock

Abstract: We investigate the sensitivity of the Large Hadron Collider to supersymmetric setups using monotop probes in which the signal is a single top quark produced in association with missing transverse energy. Our prospective study relies on Monte Carlo simulations of 300 invfb of proton- proton collisions at a centre-of-mass energy of 14 TeV and considers both leptonic and hadronic monotop decays. We p… ▽ More We investigate the sensitivity of the Large Hadron Collider to supersymmetric setups using monotop probes in which the signal is a single top quark produced in association with missing transverse energy. Our prospective study relies on Monte Carlo simulations of 300 invfb of proton- proton collisions at a centre-of-mass energy of 14 TeV and considers both leptonic and hadronic monotop decays. We present analysis strategies sensitive to regions of the supersymmetric parameter space which feature small superparticle mass splittings and illustrate their strengths in the context of a particular set of benchmark scenarios. Finally, we compare the regions of parameter space expected to be accessible with monotops probes during the next run of the LHC to the reach of more traditional search strategies employed by the ATLAS and CMS collaborations, where available. △ Less

Submitted 18 June, 2015; v1 submitted 15 August, 2014; originally announced August 2014.

Comments: 11 pages, 7 figures, 1 table; version accepted by EPJC

Report number: CERN-PH-TH-2014-154, IPPP/14/75, DCPT/14/150, MCNET-14-17

Journal ref: Eur. Phys. J. C75 (2015) 7, 308

Les Houches 2013: Physics at TeV Colliders: New Physics Working Group Report

Authors: G. Brooijmans, R. Contino, B. Fuks, F. Moortgat, P. Richardson, S. Sekmen, A. Weiler, A. Alloul, A. Arbey, J. Baglio, D. Barducci, A. J. Barr, L. Basso, M. Battaglia, G. Bélanger, A. Belyaev, J. Bernon, A. Bharucha, O. Bondu, F. Boudjema, E. Boos, M. Buchkremer, V. Bunichev, G. Cacciapaglia, G. Chalons , et al. (65 additional authors not shown)

Abstract: We present the activities of the "New Physics" working group for the "Physics at TeV Colliders" workshop (Les Houches, France, 3--21 June, 2013). Our report includes new computational tool developments, studies of the implications of the Higgs boson discovery on new physics, important signatures for searches for natural new physics at the LHC, new studies of flavour aspects of new physics, and ass… ▽ More We present the activities of the "New Physics" working group for the "Physics at TeV Colliders" workshop (Les Houches, France, 3--21 June, 2013). Our report includes new computational tool developments, studies of the implications of the Higgs boson discovery on new physics, important signatures for searches for natural new physics at the LHC, new studies of flavour aspects of new physics, and assessments of the interplay between direct dark matter searches and the LHC. △ Less

Submitted 7 May, 2014; originally announced May 2014.

Comments: Proceedings of the New Physics Working Group of the 2013 Les Houches Workshop, Physics at TeV Colliders, Les Houches 3-21 June 2013. 201 pages

Herwig++ 2.7 Release Note

Authors: J. Bellm, S. Gieseke, D. Grellscheid, A. Papaefstathiou, S. Platzer, P. Richardson, C. Rohr, T. Schuh, M. H. Seymour, A. Siodmok, A. Wilcock, B. Zimmermann

Abstract: A new release of the Monte Carlo event generator Herwig++ (version 2.7) is now available. This version comes with a number of improvements including: an interface to the Universal FeynRules Output (UFO) format allowing the simulation of a wide range of new-physics models; developments of the Matchbox framework for next-to-leading order (NLO) simulations; better treatment of QCD radiation in heavy… ▽ More A new release of the Monte Carlo event generator Herwig++ (version 2.7) is now available. This version comes with a number of improvements including: an interface to the Universal FeynRules Output (UFO) format allowing the simulation of a wide range of new-physics models; developments of the Matchbox framework for next-to-leading order (NLO) simulations; better treatment of QCD radiation in heavy particle decays in new-physics models; a new tune of underlying event and colour connection parameters that allows a good simultaneous description of both Tevatron and LHC underlying event data and the effective cross-section parameter for double-parton scattering. △ Less

Submitted 25 October, 2013; originally announced October 2013.

Comments: erwig++

Report number: IPPP/13/88, MCnet-13-15, DCPT/13/176, DESY 13-186, KA-TP-31-2013, ZU-TH 23/13

A compact rotating dilution refrigerator

Authors: M. J. Fear, P. M. Walmsley, D. A. Chorlton, D. E. Zmeev, S. J. Gillott, M. C. Sellers, P. P. Richardson, H. Agrawal, G. Batey, A. I. Golov

Abstract: We describe the design and performance of a new rotating dilution refrigerator that will primarily be used for investigating the dynamics of quantized vortices in superfluid 4He. All equipment required to operate the refrigerator and perform experimental measurements is mounted on two synchronously driven, but mechanically decoupled, rotating carousels. The design allows for relative simplicity of… ▽ More We describe the design and performance of a new rotating dilution refrigerator that will primarily be used for investigating the dynamics of quantized vortices in superfluid 4He. All equipment required to operate the refrigerator and perform experimental measurements is mounted on two synchronously driven, but mechanically decoupled, rotating carousels. The design allows for relative simplicity of operation and maintenance and occupies a minimal amount of space in the laboratory. Only two connections between the laboratory and rotating frames are required for the transmission of electrical power and helium gas recovery. Measurements on the stability of rotation show that rotation is smooth to around 0.001 rad/s up to angular velocities in excess of 2.5 rad/s. The behavior of a high-Q mechanical resonator during rapid changes in rotation has also been investigated. △ Less

Submitted 12 September, 2013; originally announced September 2013.

Comments: 6 pages, 5 figures

Journal ref: Rev. Sci. Instrum. 84, 103905 (2013)

Monte Carlo Simulation of Hard Radiation in Decays in Beyond the Standard Model Physics in Herwig++

Authors: Peter Richardson, Alexandra Wilcock

Abstract: We use the POWHEG formalism in the Herwig++ event generator to match QCD real-emission matrix elements with the parton shower for a range of decays relevant to Beyond the Standard Model physics searches. Applying this correction affects the shapes of experimental observables and so changes the number of events passing selection criteria. To validate this approach, we study the impact of the correc… ▽ More We use the POWHEG formalism in the Herwig++ event generator to match QCD real-emission matrix elements with the parton shower for a range of decays relevant to Beyond the Standard Model physics searches. Applying this correction affects the shapes of experimental observables and so changes the number of events passing selection criteria. To validate this approach, we study the impact of the correction on Standard Model top quark decays. We then illustrate the effect of the correction on Beyond the Standard Model scenarios by considering the invariant-mass distribution of dijets produced in the decay of the lightest Randall-Sundrum graviton and transverse momentum distributions for decays in Supersymmetry. We consider only the effect of the POWHEG correction on the simulation of the hardest emission in the shower and ignore the normalisation factor required to correct the total widths and branching ratios to next-to-leading order accuracy. △ Less

Submitted 14 January, 2014; v1 submitted 19 March, 2013; originally announced March 2013.

Comments: 20 pages, 7 figures

Report number: IPPP/13/17, DCPT/13/34, MCNET-13-03

Journal ref: Eur.Phys.J. C74 (2014) 2713

Next-to-Leading Order Simulation of Slepton Pair Production

Authors: Ilan Fridman-Rojas, Peter Richardson

Abstract: The next-to-leading order (NLO) corrections to Drell-Yan slepton pair production are merged with parton shower evolution via the POWHEG method in Herwig++. The NLO corrections at the level of event generation alter the shape of observables in a non-global way, thereby potentially affecting the fraction of signal events which pass crucial transverse momentum cuts on decay products and missing trans… ▽ More The next-to-leading order (NLO) corrections to Drell-Yan slepton pair production are merged with parton shower evolution via the POWHEG method in Herwig++. The NLO corrections at the level of event generation alter the shape of observables in a non-global way, thereby potentially affecting the fraction of signal events which pass crucial transverse momentum cuts on decay products and missing transverse momentum requirements on events. This effect is not captured by an overall rescaling of the cross section and can have repercussions on the reach of LHC searches. △ Less

Submitted 1 August, 2012; originally announced August 2012.

Comments: 12 pages, 3 figures

Report number: IPPP/12/55; DCPT/12/110; MCNET-12-11

Investigation of Monte Carlo Uncertainties on Higgs Boson searches using Jet Substructure

Authors: Peter Richardson, David Winn

Abstract: We present an investigation of the dependence of searches for boosted Higgs bosons using jet substructure on the perturbative and non-perturbative parameters of the Herwig++ Monte Carlo event generator. Values are presented for a new tune of the parameters of the event generator, together with the an estimate of the uncertainties based on varying the parameters around the best-fit values. We present an investigation of the dependence of searches for boosted Higgs bosons using jet substructure on the perturbative and non-perturbative parameters of the Herwig++ Monte Carlo event generator. Values are presented for a new tune of the parameters of the event generator, together with the an estimate of the uncertainties based on varying the parameters around the best-fit values. △ Less

Submitted 29 July, 2012; v1 submitted 2 July, 2012; originally announced July 2012.

Comments: 23 pages v2: Minor typos fixed