Modeling Nuclear Effects in NuWro Monte Carlo Event Generator

The accurate prediction of proton-induced neutron \((p, n)\) reaction cross sections is critical for applications in nuclear engineering, medical isotope production, and astrophysics. This study introduces a machine learning framework that combines high-predictive accuracy with interpretability and uncertainty quantification. We integrate the Hiking Optimization Algorithm (<span class="sf">HOA</span>) with the eXtreme Gradient Boosting (<span class="sf">XGBoost</span>) model and employ Monte Carlo (MC) Dropout for uncertainty estimation. The framework is interpreted using SHapley Additive exPlanations (<span class="sf">SHAP</span>). First, <span class="sf">HOA</span> is utilized to navigate the high-dimensional hyperparameter space, optimizing the <span class="sf">XGBoost</span> model for performance. Subsequently, the trained model’s predictions are benchmarked against experimental data from the EXFOR database and theoretical calculations from <span class="sf">TALYS 2.0</span>. Our <span class="sf">HOA–XGBoost</span> model demonstrates better predictive accuracy over other machine learning models and provides predictions closer to experimental values than <span class="sf">TALYS 2.0</span>. The inclusion of MC Dropout provides uncertainty bounds for the model’s predictions. A detailed <span class="sf">SHAP</span> analysis reveals the underlying physical drivers of the model’s decisions: the incident proton energy (\(EN\)) is identified as the most influential feature, with its strong interaction with the reaction \(Q\)-value and product proton number (\(Z_2\)) highlighting the model’s ability to learn fundamental concepts such as reaction thresholds and the Coulomb barrier. The product nuclide’s neutron (\(N_2\)) and proton (\(Z_2\)) numbers also show influence related to nuclear stability, while the product mass number (\(A_2\)) has a lesser impact. This work presents a complementary methodology for nuclear data evaluation, paving the way for more reliable predictions and targeted experimental design. Abstract Published by the Jagiellonian University 2025 authors

In this proceedings contribution, I summarize recent developments of the spectral function approach implemented in the <span class="sf">NuWro</span> Monte Carlo event generator. The modified framework provides a consistent treatment of multinucleon final states in quasielastic scattering. The model is first validated using inclusive electron–carbon scattering data and then applied to the exclusive MicroBooNE measurements. I demonstrate that the implemented improvements play a crucial role in reproducing both the shapes and normalizations of the experimental data. Abstract Published by the Jagiellonian University 2026 authors

<div class="htmlview paragraph">Until recently, the application of the detailed chemistry approach as a predictive tool for engine modeling has been sort of a “taboo” for different reasons, mainly because of an exaggerated rigor to the chemistry/turbulence interaction modeling. In terms of this ideology, if the interaction cannot be simulated properly, the detailed chemistry approach makes no sense. The novelty of the proposed methodology is the coupling of a generalized partially stirred reactor, PaSR, model with the high efficiency numerics to treat detailed oxidation kinetics of hydrocarbon fuels. In terms of this approach, chemical processes are assumed to proceed in two successive steps: the reaction follows after the micro-mixing is completed on a sub-grid scale. Recent experimental observations on soot formation made in [<span class="xref">1</span>] and [<span class="xref">2</span>] are perfectly reproduced in the modeling, when the mechanism integrating reduced, but still comprehensive, n-heptane oxidation chemistry with kinetics of aromatics formation (see [<span class="xref">3</span>]) has been used in the simulation based on the new numerical approach incorporated into the KIVA-3 code. Finally, the model has been applied to simulation of the turbocharged Volvo AH10A245 and D12C DI Diesel engines, and the results are discussed. The soot reduction effect attributed to a shortening of fuel injection duration has been validated in the modeling.</div>

The parameters in Monte Carlo (MC) event generators are tuned on experimental measurements by evaluating the goodness of fit between the data and the MC predictions. The relative importance of each measurement is adjusted manually in an often time-consuming, iterative process to meet different experimental needs. In this work, we introduce several optimization formulations and algorithms with new decision criteria for streamlining and automating this process. These algorithms are designed for two formulations: bilevel optimization and robust optimization. Both formulations are applied to the datasets used in the ATLAS A14 tune and to the dedicated hadronization datasets generated by the SHERPA generator, respectively. The corresponding tuned generator parameters are compared using three metrics. We compare the quality of our automatic tunes to the published ATLAS A14 tune. Moreover, we analyze the impact of a pre-processing step that excludes data that cannot be described by the physics models used in the MC event generators.

The superweak force is a minimal, anomaly-free U(1) extension of the Standard Model, designed to explain the origin of <span class="it">(i)</span> neutrino masses and mixing matrix elements, <span class="it">(ii)</span> dark matter, <span class="it">(iii)</span> cosmic inflation, <span class="it">(iv)</span> stabilization of the electroweak vacuum, and <span class="it">(v)</span> leptogenesis. In this paper, we discuss the phenomenological status of the model and provide viable scenarios for the physics of the items in this list. Abstract Published by the Jagiellonian University 2025 authors

Next-to-leading order (NLO) QCD predictions coupled with parton showers, known as NLO matching, have been widely used for the precision era at the LHC. While two methods — <span class="sc">Mc@Nlo</span> and <span class="sc">Powheg</span> — have been widely adopted for this purpose, a third method, KrkNLO, has recently been described and implemented within <span class="sf">Herwig 7</span> for colour-singlet processes. We present phenomenological results of this method for the charged-current Drell–Yan process and compare with the <span class="sc">Mc@Nlo</span> method. Abstract Published by the Jagiellonian University 2025 authors

In this paper, we investigate the transverse momentum spectra of charged particles in proton–proton collisions at the LHC using detailed event-by-event simulations with the <span class="sf">PYTHIA 8</span> event generator. Rather than relying solely on average observables such as the mean transverse momentum, we analyse the full shape of the spectra across different charged-particle multiplicity intervals. Our results show that significant variations in spectral shape occur with increasing multiplicity, revealing a transition from soft to hard processes that is not captured by global mean values. Comparisons with other commonly used Monte Carlo models, including <span class="sf">Herwig 7</span> and <span class="sf">EPOS 4</span>, demonstrate that while the mean values are broadly consistent across generators, the underlying spectral shapes differ. Abstract Published by the Jagiellonian University 2025 authors

In this paper, we briefly present the Monte Carlo event generators <span class="sf">BHLUMI</span> and <span class="sf">BHWIDE</span> for small- and large-angle Bhabha scattering, respectively, and discuss possible ways of their improvements in order to satisfy precision needs of future electron–positron colliders. Abstract Published by the Jagiellonian University 2026 authors

The <span class="sf">Top–Down</span> reconstruction chain is a Monte Carlo simulation scheme that focuses on reconstructing observed extensive air showers while accounting for the muon discrepancy between the observed and simulated events. With the help of this algorithm, we try to reconstruct a particularly unique air shower observed by the Pierre Auger Observatory. The uniqueness of this observation lies in the very large depth of its maximum. We have modified the <span class="sf">Top–Down</span> chain to accommodate this unique event and present the <span class="sf">Top–Down</span> simulated events, which are the best match to the air shower studied. Abstract Published by the Jagiellonian University 2025 authors

Reconstruction of the invariant mass of the system with two tau leptons faces a challenge of lack of neutrinos in the observed final state of taus’ decays. In this work, we introduce a novel algorithm, which is comparable to other mass reconstruction algorithms in the field of mass resolution and much better considering time performance. We test its performance on Monte Carlo simulations with <span class="sf">PYTHIA</span> and <span class="sf">Delphes</span> and show that algorithm achieves an average execution time of approximately 3 ms per event, which is around two orders of magnitude faster than previous techniques, while delivering a mass resolution characterized by a standard deviation of \(22\) GeV for \(Z^0\) bosons and \(34.5\) GeV for Higgs bosons. A <span class="sf">Python</span> implementation of the method is provided in an open-source repository, facilitating broader adoption in high-energy physics analyses. Abstract Published by the Jagiellonian University 2025 authors

In the search for the pentaquark \({\mit \Theta }^+\) baryon, the world data on \(K^+n\to K^+n\) and \(K^+n\to K^0p\) reactions on the deuteron target and \(K^0p\to K^+n\) and \(K^0_{\mathrm {L}}\,p\to K^0_{\mathrm {S}}\,p\) reactions on the hydrogen target are revisited to study the isoscalar component of the scattering amplitudes. The determination of the \(s\)- and \(p\)-wave phase shifts for the two former channels on the deuteron target is presented in the low-momentum region with the uncertainty due to the deuteron form factors at forward angles discussed. For the reactions on hydrogen targets, a similarity expected from time reversal between the charge exchange processes \(K^+n\to K^0p\) and \(K^0p\to K^+n\) is exploited, while we present the analysis of the \(K_{\mathrm {L}}^0\,p\to K_{\mathrm {S}}^0\,p\) scattering based on the \(s\)-wave phase shift for low momenta combined with the \(t\)-channel \(\rho ^0(775)+\omega (782)+\phi (1020)\) vector meson exchange at high momenta. With the mass of 1535 MeV and decay width of 5 MeV, the possibility of the \({\mit \Theta }^+\) in the Breit–Wigner (BW) form is tested in the differential cross section measured by Damerell <span class="it">et al.</span> [<span class="it">Nucl. Phys. B</span> <span class="bf">94</span>, 374 (1075)] at \({P_\mathrm {Lab}}=434\) MeV/\(c\) and polarization. Our analysis suggests measuring the polarization observable rather than the differential cross section, which has sufficient sensitivity to distinguish the \({\mit \Theta }^+\) baryon among all spin and parity states \(J^P = 1/2^\pm \) and \(3/2^\pm \). Abstract Published by the Jagiellonian University 2025 authors

The High Luminosity Large Hadron Collider (HL-LHC) will provide additional challenges in the already demanding field of charged-particle-track reconstruction. The Inner Detector of the ATLAS experiment will be replaced by an all-silicon Inner Tracker (ITk) that will consist of pixel and strip subdetectors providing greater coverage in pseudorapidity spanning up to \(|\eta |=4\). The physics of heavy ions (HI) requires a different tracking setup as compared to \(pp\) collisions. This is dictated by the difference in experimental conditions, where instead of a huge number of simultaneous \(pp\) interactions per bunch crossing (up to \(\langle \mu \rangle =200\)), the HI collision events expect only one collision per bunch crossing. Despite this, a central lead-ion collision produces a huge number of charged particles to reconstruct, comparable to \(pp\) collisions at \(\langle \mu \rangle =200\). The presence of a single collision vertex enables certain optimizations but also introduces unique challenges. The ATLAS experiment has chosen A Common Tracking Software (<span class="sf">ACTS</span>) for the HL-LHC to perform track reconstruction, as it is expected to meet the new challenges ahead. This document highlights the progress in setting up the <span class="sf">ACTS</span>-based track reconstruction for HI with the ITk, shows a comparison of expected tracking performance in \(pp\) and HI events, and presents the predicted performance of <span class="sf">ACTS</span> compared to the existing tracking algorithms used by ATLAS. Abstract Published by the Jagiellonian University 2025 authors

The Monte Carlo program KoralW version 1.51 and the concurrent Monte Carlo KoralW&YFSWW3 with all background graphs and first-order corrections to W-pair production

One of the substantial sources of systematic errors in neutrino oscillation experiments that utilize neutrinos from accelerator sources stems from a lack of precision in modeling single-pion production (SPP). Oscillation analyses rely on Monte Carlo event generators (MC), providing theoretical predictions of neutrino interactions on nuclear targets. Pions produced in these processes provide a significant fraction of oscillation signal and background on both elementary scattering and detector simulation levels. Thus, it is of critical importance to develop techniques that will allow us to accommodate state-of-the-art theoretical models describing SPP into MCs. In this work, we investigate various algorithms to implement single-pion production models in Monte Carlo event generators. Based on comparison studies, we propose a novel implementation strategy that combines satisfactory efficiency with high precision in reproducing details of theoretical models predictions, including pion angular distributions. The proposed implementation is model-independent, thereby providing a framework that can include any model for SPP. We have tested the new algorithm with the Ghent low energy model for single-pion production implemented in the NuWro Monte Carlo event generator.

The possible anomalous New Physics contributions to dipole and weak dipole moments of the \(\tau \) lepton bring renewed interest in development and revisiting charge-parity violating signatures in \(\tau \)-pair production in \(Z\)-boson decay at energies of the LHC. In this paper, we discuss effects of anomalous contributions to polarisation and spin correlations in the \(\bar q q \to \tau ^+ \tau ^-\) production processes, with \(\tau \) decays included. Due to the complex nature of the resulting distributions, Monte Carlo techniques are useful, in particular for event reweighing with studied New Physics phenomena. Extensions of the Standard Model spin amplitudes, within the Improved Born Approximation used for the matrix element, are implemented in the <span class="sf">TauSpinner</span> program. This is mainly with \(\tau \) dipole and weak dipole moments in mind, but is applicable to arbitrary New Physics interactions, provided they can be encapsulated into the Standard Model \(2 \to 2\) structure of matrix element extensions. The implementation allows one also to introduce an arbitrary phase-shift between vector and axial-vector couplings of \(Z\) boson to \(\tau \) leptons, which would have impact on the observed transverse spin correlations. Basic formulas and algorithm principles are presented, together with distributions for the spin-correlation matrix. Numerical examples of impact on experimental signatures are shown in the case of \(\tau ^\pm \to \rho ^\pm \nu _\tau \to \pi ^\pm \pi ^0 \nu _\tau \) decays. Information on how to use and configure the <span class="sf">TauSpinner</span> program is given in Appendix B. Abstract Published by the Jagiellonian University 2026 authors