A Particle Transformer jet tagger contains a sparse six-head circuit whose source-relay-readout structure recovers most performance and whose residual stream preferentially encodes 2-prong energy correlators.
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A comprehensive guide to the physics and usage of PYTHIA 8.3
Mixed citation behavior. Most common role is method (61%).
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abstract
This manual describes the PYTHIA 8.3 event generator, the most recent version of an evolving physics tool used to answer fundamental questions in particle physics. The program is most often used to generate high-energy-physics collision "events", i.e. sets of particles produced in association with the collision of two incoming high-energy particles, but has several uses beyond that. The guiding philosophy is to produce and reproduce properties of experimentally obtained collisions as accurately as possible. The program includes a wide ranges of reactions within and beyond the Standard Model, and extending to heavy ion physics. Emphasis is put on phenomena where strong interactions play a major role. The manual contains both pedagogical and practical components. All included physics models are described in enough detail to allow the user to obtain a cursory overview of used assumptions and approximations, enabling an informed evaluation of the program output. A number of the most central algorithms are described in enough detail that the main results of the program can be reproduced independently, allowing further development of existing models or the addition of new ones. Finally, a chapter dedicated fully to the user is included towards the end, providing pedagogical examples of standard use cases, and a detailed description of a number of external interfaces. The program code, the online manual, and the latest version of this print manual can be found on the PYTHIA web page: https://www.pythia.org/
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- abstract This manual describes the PYTHIA 8.3 event generator, the most recent version of an evolving physics tool used to answer fundamental questions in particle physics. The program is most often used to generate high-energy-physics collision "events", i.e. sets of particles produced in association with the collision of two incoming high-energy particles, but has several uses beyond that. The guiding philosophy is to produce and reproduce properties of experimentally obtained collisions as accurately as possible. The program includes a wide ranges of reactions within and beyond the Standard Model, a
- method for the remaining data, the full range (|𝜂jet|<4.9 ) was used. In order to measure the EMD rate of0𝑛0𝑛 𝛾+𝐴→jets collisions, an additional sample was collected using the same jet trigger requirements but with an L1 ZDC trigger requiring at least one neutron on exactly one side. 5 Several Monte Carlo (MC) samples were produced for this analysis using thePythia8 event generator [45, 46] for the three relevant physical processes:𝛾+𝐴→jets , 𝛾+𝐼 𝑃→jets , and𝛾+𝛾→jets . Final-state stable particles, def
- method defined in terms of the polar angle𝜃 as 𝜂=−ln tan(𝜃/2) and is equal to the rapidity𝑦=(1/2)ln[(𝐸+𝑝 𝑧)/(𝐸−𝑝 𝑧)] in the relativistic limit. Angular distance is measured in units ofΔ𝑅≡ √︁ (Δ𝑦) 2 + (Δ𝜙) 2. 3 QBH MC signal samples were generated using theQBH v3.02generator [7] to compute the production cross-sections and model the hard-scatter process, assuming zero angular momentum. Events were then interfaced toPythia8 [34] to model parton showering and hadronisation. As in previous iterations of se
- method focus the discussion on experiments measuring gamma- rays and neutrinos. To accurately determine the expected signal, we first compute the full decay spectrum of the DM candidate using Monte Carlo simulations. We implement our EFT operators inFeynRules[14, 104-106] and simulate the underlying partonic events viaMadGraph5 aMC[107, 108], which is subsequently interfaced withPythia8[109] for parton showering, hadronisation and decay of unstable SM particles. This procedure provides the differential
- method The following subdominant contributions are also considered: t tW, t tZ and triboson (WWW, WWZ, WZZ) production, simulated with MADGRAPH5 aMC@NLOv2.6.5 at NLO in pQCD [50, 54]. All signal and background processes are simulated using similar Monte Carlo (MC) generator configurations, utilising theNNPDF3.1 [66] NNLO parton distribution functions. All gener- ators are interfaced withPYTHIAv8.240 [67] (v8.306 [68]) for the parton shower simulation, hadronisation, and fragmentation processes for the
- background Frampton and S.L. Glashow,Unstable heavy particles,Phys. Rev. Lett.44(1980) 1481. [11] P. Gondolo, G. Gelmini and S. Sarkar,Cosmic neutrinos from unstable relic particles,Nucl. Phys. B392(1993) 111 [hep-ph/9209236]. [12] T. Kanzaki, M. Kawasaki, K. Kohri and T. Moroi,Cosmological Constraints on Neutrino Injection,Phys. Rev. D76(2007) 105017 [0705.1200]. [13] Y. Ema, R. Jinno and T. Moroi,Cosmic-Ray Neutrinos from the Decay of Long-Lived Particle and the Recent IceCube Result,Phys. Lett. B733(201
- method 1) production at1000GeV for Run 2, with slightly higher cross sections for Run 3. The decay branching ratios are set toB ( ˜𝜒± 1 →ℎℓ ±)=100% and B ( ˜𝜒0 1 →ℎ𝜈)=100% , with equal branching fractions to each lepton generation. Samples were generated withMadGraph5_aMC@NLO3.5.3 [39] with theNNPDF3.0nlo[40] parton distribution function (PDF). The parton shower, hadronization, and underlying event were modeled usingPythia8.310 [41] with the A14 set of tuned parameters (tune) [42]. The MC setup for the
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representative citing papers
ATLAS reports an 8+ sigma excess in ttbar production near threshold, consistent with NRQCD quasi-bound states and measuring 9.3 pb.
First measurement of photonuclear D0 production cross section in ultraperipheral PbPb collisions as a function of pT and rapidity, compared to NLO pQCD with nuclear PDFs and CGC predictions.
First differential measurement of muon neutrino-nucleon cross section and flux in six TeV-scale energy bins using FASER at the LHC, with results consistent with Standard Model expectations.
Single inclusive high-PT hadron and jet production in lepton-hadron scattering is factorized using a joint QCD+QED approach with universal lepton distribution functions, and predictions are given for JLab and EIC energies.
Completes soft-operator formulation for thrust-axis TMD in e+e- and SIDIS, proposes nonperturbative model with event-shape dependence, resums logs, and validates against Pythia8.3 simulations.
First complete NLL calculations of projected energy correlators (up to 4-point) on tracks via factorization theorems and RG evolution, extending prior full-jet results.
A generalized parton shower for arbitrary gauge groups plus a Mamba network on Lund jet planes can distinguish dark gauge symmetries even when non-perturbative hadronization details are unknown.
Introduces Centauric 1-jettiness in DIS, derives N3LL resummation matched to NLO, and establishes universal non-perturbative power corrections scaling as 1/R via reduction to rescaled hemisphere soft function.
Neutral-pion nuclear modification factors in OO collisions exhibit suppression at 4.9 sigma after subtracting cold-nuclear-matter effects via pO data, consistent with parton energy loss models.
Charged energy correlators measured in jets at the LHC show like-sign pairs sensitive to parton shower models and unlike-sign pairs sensitive to hadronization, with charge-independent cold nuclear matter effects in p-Pb collisions.
A model of quantum decoherence from string breaking explains hyperon spin correlations by linking vacuum entanglement to observed data in non-perturbative QCD.
AgentRivet applies commercial LLMs in an autonomous workflow to extract physics details from ATLAS and CMS papers and generate Rivet routines, achieving few syntax errors but occasional physics implementation issues on two test cases.
Simulations show a peak in the proxy mass M_(d/2)K only when deuterons form by coalescence of protons from Λ(1520) decays, not in thermal models.
No significant excess found in low-mass dijet spectrum from pile-up collisions; exclusion limits set on Gaussian and simplified dark matter models with 1.3 pb^{-1} effective luminosity.
Computes two-loop jet functions for N=4,5,6 projected energy correlators enabling NNLL collinear resummation matched to NLO in e+e- and Higgs-to-gluons processes, with non-perturbative corrections from two universal soft matrix elements.
Nested-GPT is an autoregressive Transformer surrogate that generates variable-multiplicity parton showers while enforcing ordered Markovian branching and matches reference Monte Carlo results for leading-log non-global logarithm resummation in the large-Nc limit.
Collider-Bench is a new benchmark showing that current LLM agents cannot reliably reproduce LHC analyses at the level of a physicist-in-the-loop.
PanScales final-state showers now include quark masses at NLL accuracy while keeping original accuracy for massless observables.
Non-supersymmetric spin-3/2 dark matter with baryon-violating portals can explain the relic abundance through UV and Boltzmann-suppressed freeze-in, with viable parameter space constrained by indirect detection, direct detection, and LHC monojet searches.
First measurement of γ+IP→jets cross-sections in 0n0n ultra-peripheral Pb+Pb collisions at 5.02 TeV, achieved by statistically separating photon-pomeron, photon-photon, and peripheral photonuclear contributions via template fits to minimum rapidity gap distributions.
Hadrons from ion electromagnetic dissociation break exclusivity conditions in ultraperipheral collisions, resolving tensions in exclusive muon-pair and coherent J/ψ measurements at the LHC.
Self-normalized yields of prompt and non-prompt J/ψ increase stronger than linearly with charged-particle multiplicity in pp collisions at 13 TeV, with stronger effect in the toward azimuthal region.
ATLAS measured charged-particle production in 9.62 TeV p-O collisions, yielding a fiducial pO cross section of 396 mb and extrapolated p-air inelastic cross section of 406 mb, with distributions an order of magnitude more precise than hadronic model differences.
citing papers explorer
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Dissecting Jet-Tagger Through Mechanistic Interpretability
A Particle Transformer jet tagger contains a sparse six-head circuit whose source-relay-readout structure recovers most performance and whose residual stream preferentially encodes 2-prong energy correlators.
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Observation of a cross-section enhancement near the $t\bar{t}$ production threshold in $\sqrt{s}=13$ TeV $pp$ collisions with the ATLAS detector
ATLAS reports an 8+ sigma excess in ttbar production near threshold, consistent with NRQCD quasi-bound states and measuring 9.3 pb.
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Measurement of D$^0$ meson photoproduction in ultraperipheral heavy ion collisions
First measurement of photonuclear D0 production cross section in ultraperipheral PbPb collisions as a function of pT and rapidity, compared to NLO pQCD with nuclear PDFs and CGC predictions.
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First Measurement of the Muon Neutrino Interaction Cross Section and Flux as a Function of Energy at the LHC with FASER
First differential measurement of muon neutrino-nucleon cross section and flux in six TeV-scale energy bins using FASER at the LHC, with results consistent with Standard Model expectations.
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Single inclusive hadron and jet production in lepton-hadron scattering
Single inclusive high-PT hadron and jet production in lepton-hadron scattering is factorized using a joint QCD+QED approach with universal lepton distribution functions, and predictions are given for JLab and EIC energies.
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Event-axis TMD measurements in $e^+e^-$ and SIDIS
Completes soft-operator formulation for thrust-axis TMD in e+e- and SIDIS, proposes nonperturbative model with event-shape dependence, resums logs, and validates against Pythia8.3 simulations.
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Putting Jet Substructure on Track(s)
First complete NLL calculations of projected energy correlators (up to 4-point) on tracks via factorization theorems and RG evolution, extending prior full-jet results.
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Disentangling Dark Gauge Symmetries with Deep Learning on the Lund Jet Plane
A generalized parton shower for arbitrary gauge groups plus a Mamba network on Lund jet planes can distinguish dark gauge symmetries even when non-perturbative hadronization details are unknown.
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Centauric 1-Jettiness in DIS and Universal Power Corrections
Introduces Centauric 1-jettiness in DIS, derives N3LL resummation matched to NLO, and establishes universal non-perturbative power corrections scaling as 1/R via reduction to rescaled hemisphere soft function.
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Evidence for parton energy loss in oxygen$-$oxygen collisions at $\mathbf{\sqrt{s_{\rm NN}}=5.36}$ TeV
Neutral-pion nuclear modification factors in OO collisions exhibit suppression at 4.9 sigma after subtracting cold-nuclear-matter effects via pO data, consistent with parton energy loss models.
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Probing jet evolution with charged energy correlators in small systems
Charged energy correlators measured in jets at the LHC show like-sign pairs sensitive to parton shower models and unlike-sign pairs sensitive to hadronization, with charge-independent cold nuclear matter effects in p-Pb collisions.
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Quantum decoherence of hyperon spin correlations in QCD hadronization
A model of quantum decoherence from string breaking explains hyperon spin correlations by linking vacuum entanglement to observed data in non-perturbative QCD.
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AgentRivet: an automated system for producing Rivet routines from journal publications
AgentRivet applies commercial LLMs in an autonomous workflow to extract physics details from ATLAS and CMS papers and generate Rivet routines, achieving few syntax errors but occasional physics implementation issues on two test cases.
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$\Lambda$(1520) as a probe of resonance-driven deuteron formation at the LHC
Simulations show a peak in the proxy mass M_(d/2)K only when deuterons form by coalescence of protons from Λ(1520) decays, not in thermal models.
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Search for electroweak scale dijet resonances in pile-up collisions at $\sqrt{s}=13$ TeV with the ATLAS detector
No significant excess found in low-mass dijet spectrum from pile-up collisions; exclusion limits set on Gaussian and simplified dark matter models with 1.3 pb^{-1} effective luminosity.
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Projected Energy Correlators: Two-Loop Jet Functions and NNLL Resummation
Computes two-loop jet functions for N=4,5,6 projected energy correlators enabling NNLL collinear resummation matched to NLO in e+e- and Higgs-to-gluons processes, with non-perturbative corrections from two universal soft matrix elements.
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Nested-GPT for variable-multiplicity parton showers: A case study in the resummation of non-global logarithms
Nested-GPT is an autoregressive Transformer surrogate that generates variable-multiplicity parton showers while enforcing ordered Markovian branching and matches reference Monte Carlo results for leading-log non-global logarithm resummation in the large-Nc limit.
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Collider-Bench: Benchmarking AI Agents with Particle Physics Analysis Reproduction
Collider-Bench is a new benchmark showing that current LLM agents cannot reliably reproduce LHC analyses at the level of a physicist-in-the-loop.
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Logarithmically-accurate showers with massive quarks
PanScales final-state showers now include quark masses at NLL accuracy while keeping original accuracy for massless observables.
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Decaying spin-3/2 dark matter from baryon number violation
Non-supersymmetric spin-3/2 dark matter with baryon-violating portals can explain the relic abundance through UV and Boltzmann-suppressed freeze-in, with viable parameter space constrained by indirect detection, direct detection, and LHC monojet searches.
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Measurement of jet photoproduction in ultra-peripheral Pb+Pb collisions without nuclear breakup at $\sqrt{s_\mathrm{NN}} = 5.02$ TeV with the ATLAS detector
First measurement of γ+IP→jets cross-sections in 0n0n ultra-peripheral Pb+Pb collisions at 5.02 TeV, achieved by statistically separating photon-pomeron, photon-photon, and peripheral photonuclear contributions via template fits to minimum rapidity gap distributions.
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A First Account of the Impact of Ion Electromagnetic Dissociation on Event Exclusivity in Ultraperipheral LHC Collisions
Hadrons from ion electromagnetic dissociation break exclusivity conditions in ultraperipheral collisions, resolving tensions in exclusive muon-pair and coherent J/ψ measurements at the LHC.
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Multiplicity dependence of prompt and non-prompt J/$\psi$ production at midrapidity in pp collisions at $\sqrt{s} = 13$ TeV
Self-normalized yields of prompt and non-prompt J/ψ increase stronger than linearly with charged-particle multiplicity in pp collisions at 13 TeV, with stronger effect in the toward azimuthal region.
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Measurement of charged-particle production in $\sqrt{s_\text{NN}}=9.62$ TeV proton-oxygen collisions as a probe of cosmic-ray air showers with the ATLAS detector
ATLAS measured charged-particle production in 9.62 TeV p-O collisions, yielding a fiducial pO cross section of 396 mb and extrapolated p-air inelastic cross section of 406 mb, with distributions an order of magnitude more precise than hadronic model differences.
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Probing compressed triplet scalars with ISR jets and soft leptons at the LHC
A cut-and-count analysis exploiting ISR jets and soft leptons can reach discovery sensitivity for compressed triplet scalars with 1-30 GeV splittings at 3000 fb^{-1}.
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Data-Driven Predictions for Dark Photon and Millicharged Particle Production
A data-driven framework using normalizing flows predicts the rate and kinematic distributions of dark photon and millicharged particle production directly from measured dilepton events.
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Jet fragmentation function and groomed substructure of bottom quark jets in proton-proton collisions at 5.02 TeV
CMS measures soft-drop groomed radius and momentum balance plus a charged fragmentation function for b jets, observing dead-cone suppression compared to inclusive jets.
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Observation of suppressed charged-particle production in ultrarelativistic oxygen-oxygen collisions
First measurement of the nuclear modification factor R_AA in OO collisions at 5.36 TeV shows suppression with a minimum of 0.69 at p_T around 6 GeV, favoring models with parton energy loss.
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Bayesian Constraints on Pre-Equilibrium Jet Quenching and Predictions for Oxygen Collisions
Bayesian constraints on early-time jet quenching from large collision systems yield predictions of measurable energy loss in oxygen-oxygen collisions.
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Determination of Fragmentation Functions from Charge Asymmetries in Hadron Production
Non-singlet fragmentation functions of pions and kaons are determined at NNLO QCD from charge asymmetry measurements in e+e- annihilation and SIDIS, yielding a scaling index of 0.7 and strangeness suppression of 0.5.
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IAFormer: Interaction-Aware Transformer network for collider data analysis
IAFormer uses boost-invariant pairwise quantities and differential attention to create a sparse Transformer that achieves state-of-the-art classification on top-quark and quark-gluon jet datasets while using over an order of magnitude fewer parameters than prior Particle Transformer models.
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Optimal-Transport-Based Cell Resampling for Negative and Pathological Event Weights
IRC-safe optimal-transport metrics (EMD, sEMD) enable lower-bias cell resampling of negative-weight NLO Monte Carlo events without intermediate jet clustering.
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Factorization of elastic, single, and double diffractive $pp$ scattering
SCET with Glauber operators factorizes elastic/single/double diffractive pp scattering, proving non-universality of hadronic functions versus ep while rapidity anomalous dimensions remain universal.
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Simultaneous efficiency measurements of $b$- and $c$-jets in $t\bar{t}$ events from $\sqrt{s}=13.6$ TeV $pp$ collision data collected with the ATLAS detector
Simultaneous measurements of b-jet tagging and c-jet mistagging efficiency scale factors for the ATLAS GN2 tagger achieve precisions below 2% and 5% respectively using 56 fb⁻¹ of 13.6 TeV ttbar data.
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A resonance-aware MC@NLO QCD+EW-matched calculation of lepton-pair production
First automated MC@NLO matching of NLO QCD+EW to an interleaved QCD+QED parton shower with resonance-aware dipole subtraction, validated for Drell-Yan lepton-pair production.
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Galactic Center Neutrinos from Cosmic Ray-Dark Matter Interactions
ANTARES Galactic Ridge neutrino observations constrain DM-nucleon elastic scattering cross sections down to keV-scale DM masses via cosmic ray–dark matter deep inelastic scattering.
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Defining a Minimum Resolution for Unbinned Analyses
The Minimum Resolution Likelihood method defines a fiducial signal region to convert ML-induced systematic effects into statistical uncertainties for unbiased signal strength estimation in collider analyses.
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The one-point charge correlator in deep inelastic scattering
Defines an IRC-safe one-point charge correlator in DIS, relates it to a new nucleon charge correlator in the forward limit and to TMDs in the back-to-back limit, with SCET derivations verified in QCD to O(alpha_s^2) and resummations to NLL/N3LL.
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High Multiplicity Trigger for Long-Lived Particles in CMS detector
CMS implements and deploys a dedicated high-multiplicity trigger targeting displaced LLP decays in the muon system for Run 3 data taking.
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Lepton number violation at hadron colliders via pseudo-Dirac heavy neutral leptons
Damped oscillations alleviate LN violation suppression for pseudo-Dirac HNLs, improving collider sensitivities and allowing distinction from the double-Majorana limit.
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Reweighting Underlying Event and Colour Reconnection parameter variations in Sherpa
A reweighting method is introduced to efficiently study and tune MPI and CR parameter variations in Sherpa using relative weights, demonstrated with LHC and Tevatron data.
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Mapping jet substructure in heavy-ion collisions with track functions
Track functions exhibit model-dependent modifications to higher moments in heavy-ion jets, with RG flows qualitatively preserved, enabling discrimination between jet quenching pictures.
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Probing Strange-Quark Hadronization via (Multi-)Strange Hadron Multiplicity Distributions in Small Collision Systems with ALICE
ALICE reports the first measurement of multiplicity probability distributions for strange hadrons in pp collisions at 5.02 TeV via event-by-event counting, compared to Monte Carlo models.
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A generalised-$k_t$ jet algorithm for Deep Inelastic Scattering
The authors define a generalised-k_t jet algorithm family for DIS in the Breit frame, extending the prior p=0 case, and test its use for struck-quark jet identification and non-perturbative effects.
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Probing pair production of long-lived scalars via an off-shell Standard-Model-like Higgs boson at the LHC
Pair production of long-lived scalars via off-shell Higgs at the LHC is probed with displaced-vertex searches, excluding masses up to ~230 GeV with current ATLAS data for a benchmark coupling.
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Energy-energy correlators inside single inclusive jets in heavy-ion collisions with CoLBT-hydro model
A multi-stage CoLBT-hydro simulation with a 2 GeV medium scale reproduces the CMS in-jet EEC and predicts rank- and rapidity-gap-dependent modifications that encode path length and the diffusion wake.
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RooAgent: An LLM Agent for Root-Based High Energy Physics Analysis
RooAgent provides an LLM agent interface that translates natural-language prompts into calls to PyROOT analysis functions for high energy physics tasks, with support for multiple AI backends and tested on ZH simulations and ATLAS open data.
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NLO QCD and parton-shower effects for Higgs-boson production in association with a hard photon via vector-boson fusion
NLO QCD plus parton-shower matched implementation for VBF Higgs plus photon production, with studies showing small shower effects on Higgs observables and larger effects on sub-leading jets.
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MeVPrtl: An Event Generator for Dark Sector Particles in the Short-Baseline Neutrino Program
MeVPrtl is a new event generator that implements Higgs portal, heavy neutral lepton, and heavy QCD axion models for use in short-baseline neutrino experiments.
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Observation of impact parameter dependent modifications of nuclear parton distributions in photonuclear Pb+Pb collisions at $\sqrt{s_\mathrm{NN}} = 5.02$ TeV with the ATLAS detector
ATLAS reports a 6 sigma observation that nuclear parton distribution modifications in photonuclear Pb+Pb collisions depend on impact parameter, shown by differing cross-section shapes versus x+ with and without forward neutron emission.