Monte Carlo Generator Research Articles

Centrality definition in e+A collisions at the Electron-Ion Collider

Abstract In this work, we investigate the feasibility of defining centrality in electron-ion collisions at the Electron-Ion Collider (EIC) by examining the correlation between the impact parameter and several observables, including total energy, total transverse momentum, and total number of particles. Using the BeAGLE Monte Carlo generator, we simulate e+Au and e+Ru collisions at different energies and analyze the correlation between the impact parameter and these observables across different kinematic regions. Our findings indicate that the correlation is weak in the central rapidity region but becomes stronger in the forward and far-forward rapidity regions. However, the correlation is not sufficiently robust to allow for precise centrality determination. We conclude that defining centrality in electron-ion collisions is more challenging than in ion-ion collisions, necessitating further studies to develop a robust centrality definition for the EIC.

New BABAR studies for the data-driven predictions of the muon g − 2

Using the full BABAR data sample, a dedicated measurement of additional radiation in e+e−→μ+μ−γ and e+e−→π+π−γ initial-state-radiation events is presented. Results are obtained at next-to-leading and next-to-next-to-leading order, with one and two additional photons, respectively, for radiation from the initial and final states. The comparison with predictions from Phokhara and AfkQed Monte Carlo generators reveals discrepancies for the former in the one-photon rates and angular distributions. While this disagreement has a negligible effect on the e+e−→π+π−(γ) cross section measured by BABAR, the impact on other cross-section measurements may be larger than uncertainties assigned. The findings shed a new light on the long-standing deviation between the muon g−2 measurement and the Standard Model prediction using the data-driven dispersive approach.

Measurements of the production cross-section for a Z boson in association with b- or c-jets in proton–proton collisions at s=13\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sqrt{s} = 13$$\\end{document} TeV with the ATLAS detector

This paper presents a measurement of the production cross-section of a Z boson in association with b- or c-jets, in proton–proton collisions at s=13\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sqrt{s} = 13$$\\end{document} TeV with the ATLAS experiment at the Large Hadron Collider using data corresponding to an integrated luminosity of 140 fb-1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {fb}^{-1}$$\\end{document}. Inclusive and differential cross-sections are measured for events containing a Z boson decaying into electrons or muons and produced in association with at least one b-jet, at least one c-jet, or at least two b-jets with transverse momentum pT>20\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$p_\ ext {T} > 20$$\\end{document} GeV and rapidity |y|<2.5\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$|y| < 2.5$$\\end{document}. Predictions from several Monte Carlo generators based on next-to-leading-order matrix elements interfaced with a parton-shower simulation, with different choices of flavour schemes for initial-state partons, are compared with the measured cross-sections. The results are also compared with novel predictions, based on infrared and collinear safe jet flavour dressing algorithms. Selected Z+≥1c\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$Z + \\ge 1~c$$\\end{document}-jet observables, optimized for sensitivity to intrinsic-charm, are compared with benchmark models with different intrinsic-charm fractions.

A new Monte Carlo generator for BSM physics in B → K*ℓ+ℓ− decays with an application to lepton non-universality in angular distributions

Within the widely used EvtGen framework, we have added a new event generator model for B → K*ℓ+ℓ− with improved standard model (SM) decay amplitudes and possible BSM physics contributions, which are implemented in the operator product expansion in terms of Wilson coefficients. This event generator can then be used to estimate the statistical sensitivity of a simulated experiment to the most general BSM signal resulting from dimension-six operators. We describe the advantages and potential of the newly developed ‘Sibidanov Physics Generator’ in improving the experimental sensitivity of searches for lepton non-universal BSM physics and clarifying signatures. The new generator can properly simulate BSM scenarios, interference between SM and BSM amplitudes, and correlations between different BSM observables as well as acceptance bias. We show that exploiting such correlations substantially improves experimental sensitivity. As a demonstration of the utility of the MC generator, we examine the prospects for improved measurements of lepton non-universality in angular distributions for B → K*ℓ+ℓ− decays from the expected 50 ab−1 data set of the Belle II experiment, using a four-dimensional unbinned maximum likelihood fit. We describe promising experimental signatures and correlations between observables. The use of lepton-universality violating ∆-observables significantly reduces uncertainties in the SM expectations due to QCD and resonance effects and is ideally suited for Belle II with the large data sets expected in the next decade. Thanks to the clean experimental environment of an e+e− machine, Belle II should be able to probe BSM physics in the Wilson coefficients C7 and C7′\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {C}_7^{\\prime } $$\\end{document}, which appear at low q2 in the di-electron channel.

Analytical formula for the cross section of hadron production from e + e − collisions around the narrow charmouinum resonances

The paper reports an analytical formula for the production cross section of e + e − annihilation to hadrons in the vicinity of a narrow resonance, particularly in the τ-charm region, while considering initial state radiation. Despite some approximations in its derivation, comparison between the analytical formula and direct integration of ISR shows good accuracy, indicating that the analytical formula meets current experimental requirements. Furthermore, this paper presents a comparison of the cross section between the analytical formula and calculations using the ConExc Monte Carlo generator. The efficiency of the analytical formula in significantly reducing computing time makes it a favorable choice for the regression procedure to extract the parameters of narrow charmonium resonances in experiments.

Test of the Model of “Running Axial Mass” Using NOvA Near Detector Data on Muon Neutrino Scattering on Nuclei

A phenomenological model of a “running axial mass” (MArun) was previously proposed to calculate cross sections for the quasielastic scattering of neutrinos and antineutrinos on nuclei. It can be easily implemented in neutrino generators and has only two free parameters, which are obtained from the global fit to the experimental data on the total and differential cross sections for the quasielastic scattering of (anti)neutrinos on various nuclear targets. In this work, the NOvA near detector data on the total and differential cross sections for the scattering of muon neutrinos, are compared to the simulation performed using the GENIE neutrino Monte Carlo generator (v.3.4.0), which optionally allows for using the MArun model.

Spectra of \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${Z}$$\\end{document} Bosons and Lepton Angular Coefficients in the Leading Approximation of the Parton Reggeization Approach with Allowance for the Next-to-Leading-Order Corrections

The production of \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$Z$$\\end{document} bosons in proton–proton collisions and the LHC energies is studied. The production cross sections for \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$Z$$\\end{document} bosons and their transverse-momentum spectra are calculated along with the lepton angular coefficients as functions of the \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$Z$$\\end{document}-boson transverse momentum. The calculations are performed within the parton Reggeization approach in the leading-order approximation in the strong coupling constant \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$(Q\\bar{Q}\ o Z)$$\\end{document} and with allowance for the next-to-leading-order correction associated with Reggeized-quark scattering on a Reggeized gluon \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$(RQ\ o Zq)$$\\end{document}. A numerical simulation is performed by means of the KaTie Monte Carlo generator. The results of the calculations are compared with experimental data of the ATLAS Collaboration.

Search for jet quenching effects in high-multiplicity pp collisions at s\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\sqrt{s} $$\\end{document} = 13 TeV via di-jet acoplanarity

The ALICE Collaboration reports a search for jet quenching effects in high-multiplicity (HM) proton-proton collisions at s\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\sqrt{s} $$\\end{document} = 13 TeV, using the semi-inclusive azimuthal-difference distribution ∆φ of charged-particle jets recoiling from a high transverse momentum (high-pT,trig) trigger hadron. Jet quenching may broaden the ∆φ distribution measured in HM events compared to that in minimum bias (MB) events. The measurement employs a pT,trig-differential observable for data-driven suppression of the contribution of multiple partonic interactions, which is the dominant background. While azimuthal broadening is indeed observed in HM compared to MB events, similar broadening for HM events is observed for simulations based on the PYTHIA 8 Monte Carlo generator, which does not incorporate jet quenching. Detailed analysis of these data and simulations show that the azimuthal broadening is due to bias of the HM selection towards events with multiple jets in the final state. The identification of this bias has implications for all jet quenching searches where selection is made on the event activity.

QGSJET-III model of high energy hadronic interactions. II. Particle production and extensive air shower characteristics

The hadronization procedure of the QGSJET-III Monte Carlo (MC) generator of high energy hadronic interactions is discussed. Selected results of the model, regarding production spectra of secondary particles, are presented in comparison to experimental data and to the corresponding predictions of the QGSJET-II-04 MC generator. The model is applied to calculations of basic characteristics of extensive air showers initiated by cosmic ray interactions in the atmosphere and the results are compared to predictions of other MC generators of cosmic ray interactions. Published by the American Physical Society 2024

JLab spectral functions of argon in nuwro and their implications for MicroBooNE

The Short-Baseline Neutrino program in Fermilab aims to resolve the nature of the low-energy excess events observed in LSND and MiniBooNE, and analyze with unprecedented precision neutrino interactions with argon. These studies require a reliable estimate of neutrino cross sections, in particular for charged current quasielastic scattering (CCQE). Here, we report updates of the uro Monte Carlo generator that, most notably, bring the state-of-the-art spectral functions to model the ground state properties of the argon nucleus, and improve the accuracy of the cross sections at low energies by accounting for the effects of the nuclear Coulomb potential. We discuss these developments in the context of electron and neutrino interactions, by comparing updated uro predictions to experimental data from Jefferson Laboratory Hall A and MicroBooNE. The MicroBooNE CCQE-dominated data are described with the χ2 per degree of freedom of 0.7, compared with 1.0 in the local Fermi gas model. The largest improvement is observed for the angular distributions of the produced protons, where the χ2 reduces nearly by half. Being obtained using the axial form factor parametrization from MINERvA, our results indicate a consistency between the CCQE measurements in MINERvA and MicroBooNE. Published by the American Physical Society 2024

One-loop electroweak radiative corrections to polarized e+e−→ZZ process

In the paper we recalculate and discuss high-precision theoretical predictions for cross sections of the process e+e−→ZZ. We assume a complete one-loop implementation and a possibility of estimating the initial state polarizations, as well as the full-phase calculation. Numerical results are provided by our Monte Carlo tools integrator and generator for typical energies and degrees of polarization of ILC and CLIC projects in two α(0) and Gμ electroweak schemes. Published by the American Physical Society 2024

Evaluation of a baseline for the study of azimuthal correlations of charmed mesons in heavy-ion collisions using PYTHIA 8 and Herwig++ models

Measurements of azimuthal correlations of charmed mesons in high-energy heavy-ion collisions can shed light on transport properties of the Quark-Gluon Plasma. The STAR experiment collected in 2014 and 2016 a large sample of Au+Au reactions at sNN\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sqrt{s_{NN}}$$\\end{document} = 200 GeV, making such a study possible. However, such a measurement in p+p collisions at the same energy is not feasible so far. To provide such a baseline, we report a model study of the azimuthal correlations between charmed mesons in p+p collisions at s\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sqrt{s}$$\\end{document} = 200 GeV, 500 GeV and 1.96 TeV. We used two Monte Carlo generators, PYTHIA 8 and Herwig++. We compare their predictions and validate them against available data from the STAR and CDF experiments to provide a reliable p+p baseline for the correlation studies in heavy-ion collisions at experiments at RHIC. We also discuss prospects for such measurements.

QGSJET-III model of high energy hadronic interactions: The formalism

The physics content of the QGSJET-III Monte Carlo generator of high energy hadronic collisions is described. In particular, a phenomenological implementation of higher twist corrections to hard parton scattering processes is discussed in some detail. Additionally addressed is the treatment of the so-called “color fluctuation” effects related to a decomposition of hadron wave functions into a number of Fock states characterized by different spatial sizes and different parton densities. Selected model results regarding the energy dependence of the total, elastic, and diffractive proton-proton cross sections are presented. Published by the American Physical Society 2024

DarkNews: A Python-based event generator for heavy neutral lepton production in neutrino-nucleus scattering

We introduce DarkNews, a lightweight Python -based Monte-Carlo generator for beyond-the-Standard-Model neutrino-nucleus scattering. The generator handles the production and decay of heavy neutral leptons via additional vector or scalar mediators, as well as through transition magnetic moments. DarkNews samples pre-computed neutrino-nucleus upscattering cross sections and heavy neutrino decay rates to produce dilepton and single-photon events in accelerator neutrino experiments. We present two case studies with differential distributions for models that can explain the MiniBooNE excess. The aim of this code is to aid the neutrino theory and experimental communities in performing searches and sensitivity studies for new particles produced in neutrino upscattering. Program summaryProgram Title: DarkNewsCPC Library link to program files:https://doi.org/10.17632/k9nh5fn4pw.1Developer's repository link:https://github.com/mhostert/DarkNews-generatorLicensing provisions: MITProgramming language: PythonNature of problem: In many theories beyond the Standard Model of particle physics, new light particles are introduced with masses below the 100 GeV scale. These can be produced by neutrino-nucleus interactions inside neutrino detectors, leaving a visible signature through their decay. To search for these signatures, experiments have to simulate the underlying physical processes, which requires detailed knowledge of the cross sections and decay rates in the model, as well as the ability to generate Monte Carlo events.Solution method: DarkNews provides the necessary tools to simulate the production of heavy neutral leptons in accelerator neutrino experiments, focusing on neutrino-nucleus scattering processes. The program's scope includes models with new mediators and three heavy neutral leptons, parameterizing a large class of theories through generic neutrino, quark, and lepton interactions. It generates weighted Monte-Carlo events using vegas and its pre-calculated differential rates.

Machine Learning for New Physics Searches in B → K*0µ+µ− Decays

We report the status of a neural network regression model trained to extract new physics (NP) parameters in Monte Carlo (MC) simulation data. We utilize a new EvtGen NP MC generator to generate B → K*0µ+µ− events according to the deviation of the Wilson Coefficient C9 from its SM value, δC9. We train a three-dimensional ResNet regression model, using images built from the angular observables and the invariant mass of the di-muon system, to extract values of δ C9 directly from the MC data samples. This work is intended for future analyses at the Belle II experiment but may also find applicability at other experiments.

Kharakteristiki proton-protonnykh stolknoveniy, smodelirovanykh s pomoshch'yu Monte-Karlo generatorov, pri energiyakh NICA

This paper presents an overview of Monte Carlo (MC) event generators for simulation of proton-proton collisions along with the results on hadron production at nuclotron-based ion collider facility (NICA) energies. Namely, mean multiplicities, mean transverse momenta, and rapidity distributions of p(), π±, K± at different collision energies are presented. We also study two-particle angular correlations for stable charged particles. Results of simulations with PYTHIA, EPOS, SMASH, and UrQMD event generators are compared to available data. Connections of studied quantities with physics mechanisms in MC generators are discussed. We suggest a tuned set of parameters to address observed discrepancies between data and PYTHIA.

QED effects in inclusive semi-leptonic B decays

We analyse in detail the QED corrections to the total decay width and the moments of the electron energy spectrum of the inclusive semi-leptonic B → Xceν decay. Our calculation includes short-distance electroweak corrections, the complete \U0001d4aa(α) partonic terms and leading-logarithmic QED effects up to OΛQCD3/mb3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\mathcal{O}\\left({\\Lambda}_{\ extrm{QCD}}^3/{m}_b^3\\right) $$\\end{document}. A comprehensive numerical comparison of our results against those obtained with the Monte Carlo (MC) tool PHOTOS is presented. While the comparison indicates good overall agreement, our computation contains QED effects not included in PHOTOS and should therefore better describe photon radiation to B → Xceν as measured by the B-factories. Our calculations represent the first steps in the construction of a fully differential higher-order QED MC generator for inclusive semi-leptonic B decays.

LHC hadronic jet generation using convolutional variational autoencoders with normalizing flows

In high energy physics, one of the most important processes for collider data analysis is the comparison of collected and simulated data. Nowadays the state-of-the-art for data generation is in the form of Monte Carlo (MC) generators. However, because of the upcoming high-luminosity upgrade of the Large Hadron Collider (LHC), there will not be enough computational power or time to match the amount of needed simulated data using MC methods. An alternative approach under study is the usage of machine learning generative methods to fulfill that task. Since the most common final-state objects of high-energy proton collisions are hadronic jets, which are collections of particles collimated in a given region of space, this work aims to develop a convolutional variational autoencoder (ConVAE) for the generation of particle-based LHC hadronic jets. Given the ConVAE’s limitations, a normalizing flow (NF) network is coupled to it in a two-step training process, which shows improvements on the results for the generated jets. The ConVAE+NF network is capable of generating a jet in , making it one of the fastest methods for this task up to now.

Resonance-aware NLOPS matching for off-shell toverline{t} + tW production with semileptonic decays

The increasingly high accuracy of top-quark studies at the LHC calls for a theoretical description of toverline{t} production and decay in terms of exact matrix elements for the full 2 → 6 process that includes the off-shell production and the chain decays of toverline{t} and tW intermediate states, together with their quantum interference. Corresponding NLO QCD calculations matched to parton showers are available for the case of dileptonic channels and are implemented in the bb4l Monte Carlo generator, which is based on the resonance-aware POWHEG method. In this paper, we present the first NLOPS predictions of this kind for the case of semileptonic channels. In this context, the interplay of off-shell toverline{t} + tW production with various other QCD and electroweak subprocesses that yield the same semileptonic final state is discussed in detail. On the technical side, we improve the resonance-aware POWHEG procedure by means of new resonance histories based on matrix elements, which enable a realistic separation of toverline{t} and tW contributions. Moreover, we introduce a general approach which makes it possible to avoid certain spurious terms that arise from the perturbative expansion of decay widths in any off-shell higher-order calculation, and which are large enough to jeopardise physical finite-width effects. These methods are implemented in a new version of the bb4l Monte Carlo generator, which is applicable to all dileptonic and semileptonic channels, and can be extended to fully hadronic channels. The presented results include a NLOPS comparison of off-shell against on-shell toverline{t} + tW production and decay, where we highlight various non-trivial aspects related to NLO and parton-shower radiation in leptonic and hadronic top decays.

Cosmic ray interactions in the atmosphere: QGSJET-III and other models

The physics content of the QGSJET-III Monte Carlo generator of high energy hadronic collisions is discussed. New theoretical approaches implemented in QGSJET-III are addressed in some detail and a comparison to alternative treatments of other cosmic ray interaction models is performed. Calculated characteristics of cosmic ray-induced extensive air showers are presented and differences between the respective results of QGSJET-III and other models are analyzed. In particular, it is demonstrated that those differences are partly caused by severe deficiencies of the other interaction models.