professor; Department of Diffractive Processes/Division of Particle and Astroparticle Physics The Henryk Niewodniczański Institute of Nuclear Physics Polish Academy of Sciences/IFJ PAN
Search for electroweak-scale dijet resonances using trigger-level analysis with the ATLAS detector in 132 fb − 1 of pp collisions at (Formula presented) = 13 TeV G. Aad, E. Aakvaag, B. Abbott, S. Abdelhameed, K. Abeling, et al. Physical Review D, 2025 This article reports on a search for dijet resonances using 132 fb − 1 of p p collision data recorded at s = 13 TeV by the ATLAS detector at the Large Hadron Collider. The search is performed solely on jets reconstructed within the ATLAS trigger to overcome bandwidth limitations imposed on conventional single-jet triggers, which would otherwise reject data from decays of sub-TeV dijet resonances. Collision events with two jets satisfying transverse momentum thresholds of p T ≥ 85 GeV and jet rapidity separation of | y * | < 0.6 are analysed for dijet resonances with invariant masses from 375 to 1800 GeV . A data-driven background estimate is used to model the dijet mass distribution from multijet processes. No significant excess above the expected background is observed. Upper limits are set at 95% confidence level on coupling values for a benchmark leptophobic axial-vector Z ′ model and on the production cross section for a new resonance contributing a Gaussian-distributed line-shape to the dijet mass distribution.
Search for events with one displaced vertex from long-lived neutral particles decaying into hadronic jets in the ATLAS muon spectrometer in pp collisions at (Formula presented) = 13 TeV G. Aad, E. Aakvaag, B. Abbott, S. Abdelhameed, K. Abeling, et al. Physical Review D, 2025 A search for events with one displaced vertex from long-lived particles using data collected by the ATLAS detector at the Large Hadron Collider is presented, using 140 fb − 1 of proton-proton collision data at s = 13 TeV recorded in 2015–2018. The search employs techniques for reconstructing vertices of long-lived particles decaying into hadronic jets in the muon spectrometer displaced between 3 m and 14 m from the primary interaction vertex. The observed number of events is consistent with the expected background and limits for several benchmark signals are determined. A scalar-portal model and a Higgs-boson-portal baryogenesis model are considered. A dedicated analysis channel is employed to target Z-boson associated long-lived particle production, including an axionlike particle and a dark photon model. For the Higgs boson model, branching fractions above 1% are excluded at 95% confidence level for long-lived particle proper decay lengths ranging from 5 cm to 40 m. For the photophobic axionlike particle model considered, this search produces the strongest limits to date for proper decay lengths greater than O ( 10 ) cm .
Weakly supervised anomaly detection for resonant new physics in the dijet final state using proton-proton collisions at (Formula presented.) with the ATLAS detector G. Aad, E. Aakvaag, B. Abbott, S. Abdelhameed, K. Abeling, et al. Physical Review D, 2025 An anomaly detection search for narrow-width resonances beyond the Standard Model that decay into a pair of jets is presented. The search is based on 139 fb − 1 of proton-proton collisions at s = 13 TeV recorded during 2015–2018 with the ATLAS detector at the Large Hadron Collider. The analysis is optimized without a particular signal model and aims to be sensitive to a broad range of new physics. It uses two different machine learning strategies to estimate the background in different signal regions. In each region, a weakly supervised classifier is trained to distinguish this background model from data. The analysis focuses on events with high transverse momentum jets reconstructed as large-radius jets. The mass and substructure of these jets are used as inputs to the classifiers. After a classifier-based selection, the distribution of the invariant mass of the two jets is used to search for potential local excesses. The model-independent results of both the anomaly detection methods show no signs of significant local excesses. In addition to model-independent results, a representative set of signal models is injected into the data, and the sensitivity of the methods to these scenarios is reported.
Search for decays of the Higgs boson into scalar particles decaying into four or six b quarks using pp collisions at (Formula presented) = 13 TeV with the ATLAS detector G. Aad, E. Aakvaag, B. Abbott, S. Abdelhameed, K. Abeling, et al. Physical Review D, 2025 A search for exotic decays of the Higgs boson H into new scalar or pseudoscalar particles that subsequently decay into b-quarks is presented. The search considers ZH production with several decay scenarios for the Higgs boson; first to a pair of identical scalars, H→2a→4b, second to a pair of scalars with different masses (ma1<ma2), either directly, H→a1a2→4b, or via a longer decay chain, H→a1a2→3a1→6b. The analysis uses proton-proton collision data at s=13 TeV collected with the ATLAS detector at the Large Hadron Collider, corresponding to an integrated luminosity of 140 fb−1. No significant excess above the Standard Model prediction is observed. The search sets upper limits at 95% confidence level on the ratio of the Higgs boson production cross section to the SM prediction times the branching ratio of Higgs bosons decaying into 4b or 6b, between 4% and 25% for σ(ZH)/σSM(ZH)×B(H→2a→4b), between 24% and 38% for σ(ZH)/σSM(ZH)×B(H→a1a2→4b), and between 10% and 20% for σ(ZH)/σSM(ZH)×B(H→a1a2→3a1→6b), depending on the masses of the scalar particles.
Evidence for Longitudinally Polarized W Bosons in the Electroweak Production of Same-Sign W Boson Pairs in Association with Two Jets in pp Collisions at √s = 13 TeV with the ATLAS Detector G. Aad, E. Aakvaag, B. Abbott, S. Abdelhameed, K. Abeling, et al. Physical Review Letters, 2025 This Letter reports the first evidence of electroweak production of same-sign W boson pairs where at least one of the W bosons is longitudinally polarized and the most stringent constraint to date for the production of two longitudinally polarized same-sign W bosons. The dataset used corresponds to an integrated luminosity of 140 fb−1 of proton-proton collisions at a center-of-mass energy of 13 TeV, collected with the ATLAS detector during run 2 of the Large Hadron Collider. The study is performed in final states including two same-sign leptons (electrons or muons), missing transverse momentum, and at least two jets with a large invariant mass and a large rapidity difference. Two independent fits are performed targeting the production of same-sign W bosons with at least one, or two longitudinally polarized W bosons. The observed (expected) significance of the production with at least one longitudinally polarized W boson is 3.3 (4.0) standard deviations. An observed (expected) 95% confidence level upper limit of 0.45 (0.70) fb is reported on the fiducial production cross section of two longitudinally polarized same-sign W bosons.
Azimuthal anisotropies of charged particles with high transverse momentum in Pb+Pb collisions at (Formula presented.) TeV with the ATLAS detector G. Aad, E. Aakvaag, B. Abbott, S. Abdelhameed, K. Abeling, et al. Physical Review C, 2025 A measurement is presented of elliptic (v2) and triangular (v3) azimuthal anisotropy coefficients for charged particles produced in Pb+Pb collisions at sNN=5.02 TeV using a dataset corresponding to an integrated luminosity of 0.44nb−1 collected with the ATLAS detector at the LHC in 2018. The values of v2 and v3 are measured for charged particles over a wide range of transverse momentum (pT), 1–400 GeV, and Pb+Pb collision centrality, 0–60%, using the scalar-product and multiparticle cumulant methods. These methods are sensitive to event-by-event fluctuations and nonflow effects in the measurements of azimuthal anisotropies. Positive values of v2 are observed up to a pT of approximately 100 GeV from both methods across all centrality intervals. Positive values of v3 are observed up to approximately 25 GeV using both methods, though the application of the three-subevent technique to the multiparticle cumulant method leads to significant changes at the highest pT. At high pT (pT⪆10 GeV), charged particles are dominantly from jet fragmentation. These jets, and hence the measurements presented here, are sensitive to the path-length dependence of parton energy loss in the quark-gluon plasma produced in Pb+Pb collisions.
Search for cascade decays of charged sleptons and sneutrinos in final states with three leptons and missing transverse momentum in pp collisions ffiffi at √s = 13 TeV with the ATLAS detector G. Aad, E. Aakvaag, B. Abbott, S. Abdelhameed, K. Abeling, et al. Physical Review D, 2025 A search for cascade decays of charged sleptons and sneutrinos using final states characterized by three leptons (electrons or muons) and missing transverse momentum is presented. The analysis is based on a dataset with 140 fb−1 of proton-proton () collisions at a center-of-mass energy of s=13 TeV recorded by the ATLAS detector at the Large Hadron Collider. This paper focuses on a supersymmetric scenario that is motivated by the muon anomalous magnetic moment observation, dark-mattter relic density abundance, and electroweak naturalness. A mass spectrum involving light Higgsinos and heavier sleptons with a bino at intermediate mass is targeted. No significant deviation from the Standard Model expectation is observed. This search enables us to place stringent constraints on this model, excluding at the 95% confidence level charged slepton and sneutrino masses up to 450 GeV when assuming a lightest neutralino mass of 100 GeV and mass-degenerate selectrons, smuons and sneutrinos.
An implementation of neural simulation-based inference for parameter estimation in ATLAS Gilles Louppe, James Howarth Reports on Progress in Physics, 2025 Neural simulation-based inference (NSBI) is a powerful class of machine-learning-based methods for statistical inference that naturally handles high-dimensional parameter estimation without the need to bin data into low-dimensional summary histograms. Such methods are promising for a range of measurements, including at the Large Hadron Collider, where no single observable may be optimal to scan over the entire theoretical phase space under consideration, or where binning data into histograms could result in a loss of sensitivity. This work develops a NSBI framework for statistical inference, using neural networks to estimate probability density ratios, which enables the application to a full-scale analysis. It incorporates a large number of systematic uncertainties, quantifies the uncertainty due to the finite number of events in training samples, develops a method to construct confidence intervals, and demonstrates a series of intermediate diagnostic checks that can be performed to validate the robustness of the method. As an example, the power and feasibility of the method are assessed on simulated data for a simplified version of an off-shell Higgs boson couplings measurement in the four-lepton final states. This approach represents an extension to the standard statistical methodology used by the experiments at the Large Hadron Collider, and can benefit many physics analyses.
Timing detectors for forward physics Rafał Staszewski, Janusz J. Chwastowski Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment, 2019
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Measurement of the luminosity in the ZEUS experiment at HERA II L. Adamczyk, J. Andruszkow, T. Bold, P. Borzemski, C. Buettner, et al. Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment, 2014
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High-ET dijet photoproduction at HERA S. Chekanov, M. Derrick, S. Magill, B. Musgrave, D. Nicholass, et al. Physical Review D Particles Fields Gravitation and Cosmology, 2007
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Aerogel Cherenkov detectors for the luminosity measurement at HERA Janusz Chwastowski, Jan Figiel, Andrzej Kotarba, Krystyna Olkiewicz, Leszek Suszycki Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment, 2003
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D* production in deep inelastic scattering at HERA J. Breitweg, M. Derrick, D. Krakauer, S. Magill, D. Mikunas, et al. Physics Letters Section B Nuclear Elementary Particle and High Energy Physics, 1997
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Dijet cross sections in photoproduction at HERA M. Derrick, D. Krakauer, S. Magill, D. Mikunas, B. Musgrave, et al. Physics Letters Section B Nuclear Elementary Particle and High Energy Physics, 1995
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Strange meson production in e+e- annihilation TASSO Collaboration, W. Braunschweig, R. Gerhards, F. J. Kirschfink, H. -U. Martyn, et al. Zeitschrift Fur Physik C Particles and Fields, 1990
Strange baryon production in e+e- annihilation TASSO Collaboration, W. Braunschweig, R. Gerhards, F. J. Kirschfink, H. -U. Martyn, et al. Zeitschrift Fur Physik C Particles and Fields, 1989
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