19 research outputs found
First evidence of standard model pp â tttt production and performance studies of the ATLAS tile calorimeter for HL-LHC
In diesem Dokument werden zwei Analysen auf dem Gebiet der Teilchenphysik vorgestellt. Erstens, Studien ĂŒber die Performanz der Rekonstruktion von Myonen unter Verwendung von Kalorimeterinformationen wĂ€hrend der HL-LHC Phase des ATLAS Detektors. Zweitens, die Suche nach der simultanen Produktion von vier Top-Quarks, wie vom Standard Modell (SM) prognostiziert, unter Verwendung des vollstĂ€ndigen Run-II-Datensatzes, der von ATLAS aufgenommen wurde. Dieser Datensatz entspricht einer integrierten LuminositĂ€t von L = 139 fb-1 von ProtonâProton Kollisionen bei einer Schwerpunktsenergie von âs = 13 TeV.
FĂŒr diese Arbeit wird die Performanz der Rekonstruktion von Myonen fĂŒr verschiedene pile-up Szenarien untersucht, wie sie fĂŒr die HL-LHC-Phase erwartet werden, und im Hinblick auf verschiedene Rauschszenarien, die den Verlust der Energieauflösung und die Verschlechterung der Detektorakzeptanz aufgrund von Alterung und Bestrahlung der Detektorkomponenten nachbilden. Diese Studie wird durchgefĂŒhrt, um vorgeschlagene Szenarien fĂŒr die AufrĂŒstung des Detektors vor ihrer Implementierung zu testen. Die Suche nach der vom SM prognostizierten Produktion von vier Top-Quarks, konzentriert sich auf die Zerfallsmoden mit zwei Leptonen gleicher Ladung oder mehr Leptonen im Endzustand. Die Suche nach diesem Prozess ist unter anderem durch die sehr hohen involvierten Energien motiviert und durch die Tatsache, dass derzeit verfĂŒgbare DatensĂ€tze möglicherweise fĂŒr eine Entdeckung ausreichen. Die finalen Messergebnisse werden mit einem Profile-Likelihood-Fit erzielt, der das Ergebnis eines Boosted-Decision-Trees beinhaltet, welcher darauf trainiert ist zwischen Signal und Untergrund zu unterscheiden. Der Fit fĂŒhrt zu einem Wirkungsquerschnitt von Ï(pâtt ÂŻtt ÂŻ )=24(+7-6)fb, was einer beobachteten (erwarteten) Signifikanz von Z = 4,3 (Z = 2,4) entspricht. Dies reprĂ€sentiert den ersten Nachweis (Evidence) fĂŒr diesen Prozess. Das erhaltene Ergebnis ist mit der SM Vorhersage innerhalb von 1,7 Standardabweichungen kompatibel.
Auf diesen ersten Nachweis aufbauend, wird die Möglichkeit der Rekonstruktion des vier Top-Quark Systems unter Verwendung eines kinematischen Likelihood Fits entwickelt und getestet. Die Entwicklungen und Tests werden mit dem KLFitter Software Paket durchgefĂŒhrt und erzielen eine Effizienz der korrekten Zuordnung aller vier Top-Quarks von Δ = 33 ± 4 % unter optimalen Bedingungen fĂŒr den Endzustand mit einem Lepton.Two analyses in the field of particle physics are presented in this document. First,studies on the performance of the reconstruction of muons using calorimeter inform-ation under the conditions of the High-Luminosity Large-Hadron-Collider (HL-LHC)phase of theATLASdetector. Second, the search for the Standard Model (SM) sim-ultaneous production of four top quarks using the full Run-II data set recorded byATLAS. This data set corresponds to an integrated luminosity ofL= 139 fbâ1ofprotonâproton collisions at a centre of mass energy ofâs= 13 TeV.Here, the performance of the reconstruction of muons is probed for different pile-upscenarios, as those expected for the HL-LHC phase, and in light of different noise scen-arios that emulate the loss of energy resolution and deterioration of detector acceptancedue to ageing and irradiation of detector components. This study is conducted to testproposed detector upgrade scenarios before their implementation.The search for SM like four top quark production presented here, focuses on the de-cay modes with two same sign or more leptons in the final state. The search for thisprocess is, among other factors, motivated by the very large energies involved and bythe fact that it is likely on the verge of being discovered with currently available datasets. The final results are obtained in a profile likelihood fit involving the outcome of aboosted decision tree trained to discriminate between signal and background. The fitresults in a production cross section ofÏ(ppâtt tt) = 24+7â6fb, which correspondsto an observed (expected) significance ofZ= 4.3(Z= 2.4). This represents the firstevidence for this process. The obtained result is compatible with the SM prediction within 1.7 standard deviations.Following first evidence, the possibility of reconstructing the four top quark systemusing a kinematic likelihood approach is developed and tested. These developmentsare performed with theKLFitter tool set and yield an efficiency of correctlymatching all four top quarks of Δ = 33±4 %under optimal conditions in the singlelepton final state
New Angles on Fast Calorimeter Shower Simulation
The demands placed on computational resources by the simulation requirements
of high energy physics experiments motivate the development of novel simulation
tools. Machine learning based generative models offer a solution that is both
fast and accurate. In this work we extend the Bounded Information Bottleneck
Autoencoder (BIB-AE) architecture, designed for the simulation of particle
showers in highly granular calorimeters, in two key directions. First, we
generalise the model to a multi-parameter conditioning scenario, while
retaining a high degree of physics fidelity. In a second step, we perform a
detailed study of the effect of applying a state-of-the-art particle flow-based
reconstruction procedure to the generated showers. We demonstrate that the
performance of the model remains high after reconstruction. These results are
an important step towards creating a more general simulation tool, where
maintaining physics performance after reconstruction is the ultimate target.Comment: 26 pages, 19 figure
Radio Galaxy Classification with wGAN-Supported Augmentation
Novel techniques are indispensable to process the flood of data from the new
generation of radio telescopes. In particular, the classification of
astronomical sources in images is challenging. Morphological classification of
radio galaxies could be automated with deep learning models that require large
sets of labelled training data. Here, we demonstrate the use of generative
models, specifically Wasserstein GANs (wGAN), to generate artificial data for
different classes of radio galaxies. Subsequently, we augment the training data
with images from our wGAN. We find that a simple fully-connected neural network
for classification can be improved significantly by including generated images
into the training set.Comment: 10 pages, 6 figures; accepted to ml.astro; v2: matches published
versio
Recent highlights of top-quark physics with the ATLAS Experiment - FPCP2020
Four recent measurements in different areas of top-quark physics are presented. Comprehensive measurements of differential cross-sections of top-quark-antiquark pair-production are performed in the all-hadronic channel. The top-quarks and top-quark-pairs are fully reconstructed and kinematic distributions of these objects are measured at the particle and at the parton level. The measurements in the all-hadronic channel complement measurements previously performed in the lepton+jets channels in terms of range and resolution. The cross sections for the production of top quark pairs in association to a photon (ttgamma) or to a Z boson (ttZ) are measured both inclusively and differentially as a function of kinematic variables characterizing the tt+boson system. Both sets of measurements use the full Run2 data set consisting of 139/fb of integrated luminosity. Final states with three and four leptons and b-jets are used to extract ttZ rates, while tt+gamma cross sections are derived from final states with one photon, one electron and one muon of opposite sign and at least two jets. The measurements are compared to predictions obtained by NLO+PS Monte Carlo and fixed order NLO calculations. The hard scattering process in which two top-quark-antiquark pairs are produced is also called four-top-quarks production and is predicted to have a small cross-section of 12 fb in the standard model. This very rare process has not been observed yet. The background is mainly given by top-quark-antiquark production in association with heavy flavor jets. In this presentation, two analyses are presented which aim to establish experimental evidence for this process based on the full Run 2 dataset recorded with the ATLAS detector. The first analysis selects events with exactly one charged lepton and several jets or two charged leptons of opposite electric charge. The second analysis is based on a lepton pair with the same electric charge or events with more than two leptons. In both channels multivariate techniques are used to optimize the separation between signal and background events and enhance the sensitivity. Finally, both channels are combined
PremiĂšre Ă©vidence de la production pp â tttt dans le cadre du modĂšle standard et Ă©tudes de performance du calorimĂštre Ă tuiles d'ATLAS pour la phase HL-LHC
Two analyses in the field of particle physics are presented in this document. First, studies on the performance of the reconstruction of muons using calorimeter information under the conditions of the High-Luminosity Large-Hadron-Collider (HL-LHC) phase of the ATLAS detector. Second, the search for the Standard Model (SM) simultaneous production of four top quarks using the full Run-II data set recorded by ATLAS. This data set corresponds to an integrated luminosity of L = 139 fbâ1 of protonâproton collisions at a centre of mass energy of âs = 13 TeV. Here, the performance of the reconstruction of muons is probed for different pile-up scenarios, as those expected for the HL-LHC phase, and in light of different noise scenarios that emulate the loss of energy resolution and deterioration of detector acceptance due to ageing and irradiation of detector components. This study is conducted to test proposed detector upgrade scenarios before their implementation. The search for SM like four top quark production presented here, focuses on the decay modes with two same sign or more leptons in the final state. The search for this process is, among other factors, motivated by the very large energies involved and by the fact that it is likely on the verge of being discovered with currently available data sets. The final results are obtained in a profile likelihood fit involving the outcome of a boosted decision tree trained to discriminate between signal and background. The fit results in a production cross section of [1], which corresponds to an observed (expected) significance of Z = 4.3 (Z = 2.4). This represents the first evidence for this process. The obtained result is compatible with the SM prediction [2] within 1.7 standard deviations.Following first evidence, the possibility of reconstructing the four top quark system using a kinematic likelihood approach is developed and tested. These developments are performed with the KLFitter [3] tool set and yield an efficiency of correctly matching all four top quarks of Δ = 33 ± 4% under optimal conditions in the single lepton final state. [1] ATLAS Collaboration. âEvidence for ttÌttÌ production in the multilepton final state in protonâproton collisions at âs = 13 TeV with the ATLAS detectorâ. Eur. Phys. J. C 80 (2020) [2]Rikkert Frederix et al. âLarge NLO corrections in ttÌW ± and ttÌttÌ hadroproduction from supposedly subleading EW contributionsâ. JHEP 02 (2018) [3]Johannes Erdmann et al. âA likelihood-based reconstruction algorithm for top-quark pairs and the KLFitter frameworkâ. Nucl. Instrum. Meth. A 748 (2014)Deux analyses dans le domaine de la physique des particules sont prĂ©sentĂ©es dans ce document. PremiĂšrement, des Ă©tudes sur les performances de la reconstruction des muons Ă lâaide des informations calorimĂ©triques dans les conditions de la phase HL-LHC du dĂ©tecteur ATLAS.. DeuxiĂšmement, la recherche de la production simultanĂ©e de quatre quarks top en utilisant lâensemble complet des donnĂ©es Run-II enregistrĂ©es par ATLAS. Cet ensemble des donnĂ©es correspond Ă une luminositĂ© intĂ©grĂ©e de L = 139 fbâ1 des collisions protons-protons Ă un Ă©nergie dans le centre de masse de âs = 13 TeV. La performance de la reconstruction des muons est sondĂ©e pour diffĂ©rentes conditions de prise de donnĂ©es, en particulier avec des nombres de collisions parasites importants tels quâattendu pour la phase du HL-LHC. La performance est Ă©galement sondĂ© et en vue de diffĂ©rents scĂ©narios des bruits qui Ă©mulent la perte de rĂ©solution Ă©nergĂ©tique et la dĂ©tĂ©rioration de lâacceptation du dĂ©tecteur due au vieillissement et Ă lâirradiation des composants du dĂ©tecteur. Cette Ă©tude est menĂ©e pour tester les scĂ©narios proposĂ©s de mise Ă jour du dĂ©tecteur avant leur mise en Ćuvre. La recherche de la production de quatre quark top, prĂ©dite par le modĂšle standard (SM), prĂ©sentĂ©e ici, se concentre sur les modes de dĂ©sintĂ©gration avec deux leptons de mĂȘme signe ou plusieurs leptons dans lâĂ©tat final. La recherche de ce processus est, entre autres facteurs, motivĂ©e par les trĂšs grandes Ă©nergies impliquĂ©es et par le fait quâil est potentiellement sur le point dâĂȘtre dĂ©couvert avec lâensemble des donnĂ©es actuellement disponibles. Les rĂ©sultats finaux sont obtenus dans lâajustement dâune fonction de vraisemblance profilĂ©e impliquant le rĂ©sultat dâun boosted decision tree, entraĂźnĂ© Ă discriminer entre le signal et les bruits de fond. Lâajustement donne une section efficace de [1], ce qui correspond Ă une significance observĂ©e (attendue) de Z = 4,3 (Z = 2,4). Cela correspond Ă la premiĂšre Ă©vidence de ce processus. Le rĂ©sultat obtenu est compatible avec la prĂ©diction du SM [2] Ă 1,7 Ă©cart-type prĂšs. AprĂšs la premiĂšre Ă©vidence, la possibilitĂ© de reconstruire le systĂšme des quatre quark top en utilisant une approche de vraisemblance cinĂ©matique est explorĂ©e. Les Ă©tudes sont effectuĂ©es dans lâĂ©tat final avec un seul lepton avec lâoutil KLFitter [3] donnant une efficacitĂ© de correspondance correcte des quatre quarks top de Δ = 33 ± 4 % dans des conditions optimales. [1] ATLAS Collaboration. âEvidence for ttÌttÌ production in the multilepton final state in protonâproton collisions at âs = 13 TeV with the ATLAS detectorâ. Eur. Phys. J. C 80 (2020) [2]Rikkert Frederix et al. âLarge NLO corrections in ttÌW ± and ttÌttÌ hadroproduction from supposedly subleading EW contributionsâ. JHEP 02 (2018) [3]Johannes Erdmann et al. âA likelihood-based reconstruction algorithm for top-quark pairs and the KLFitter frameworkâ. Nucl. Instrum. Meth. A 748 (2014
New Angles on Fast Calorimeter Shower Simulation
The demands placed on computational resources by the simulation requirements of high energy physics experiments motivate the development of novel simulation tools. Machine learning based generative models offer a solution that is both fast and accurate. In this work we extend the Bounded Information Bottleneck Autoencoder (BIB-AE) architecture, designed for the simulation of particle showers in highly granular calorimeters, in two key directions. First, we generalise the model to a multi-parameter conditioning scenario, while retaining a high degree of physics fidelity. In a second step, we perform a detailed study of the effect of applying a state-of-the-art particle flow-based reconstruction procedure to the generated showers. We demonstrate that the performance of the model remains high after reconstruction. These results are an important step towards creating a more general simulation tool, where maintaining physics performance after reconstruction is the ultimate target
Hadrons, better, faster, stronger
Motivated by the computational limitations of simulating interactions of particles in highly-granular detectors, there exists a concerted effort to build fast and exact machine-learning-based shower simulators. This work reports progress on two important fronts. First, the previously investigated Wasserstein generative adversarial network and bounded information bottleneck autoencoder generative models are improved and successful learning of hadronic showers initiated by charged pions in a segment of the hadronic calorimeter of the International Large Detector is demonstrated for the first time. Second, we consider how state-of-the-art reconstruction software applied to generated shower energies affects the obtainable energy response and resolution. While many challenges remain, these results constitute an important milestone in using generative models in a realistic setting
Generative Models for Shower Simulation in HEP
Simulation in High Energy Physics (HEP) places a heavy burden on the availablecomputing resources and is expected to become a major bottleneck for the upcoming highluminosity phase of the LHC and for future Higgs factories, motivating a concerted effort todevelop computationally efficient solutions. Methods based on generative machine learningmethods hold promise to alleviate the computational strain produced by simulation whileproviding the physical accuracy required of a surrogate simulator.In this contribution, an overview of a growing body of work focused on simulatingshowers in highly granular calorimeters will be reported, which is making significant stepstowards realistic fast simulation tools based on deep generative models. Progress on thesimulation of both electromagnetic and hadronic showers will be presented, with a focus onthe high degree of physical fidelity and computational performance achieved. Additional stepstaken to address the challenges faced when broadening the scope of these simulators, such asthose posed by multi-parameter conditioning, will also be discussed
Fast and Accurate Electromagnetic and Hadronic Showers from Generative Models
Generative machine learning models offer a promising way to efficiently amplify classical Monte Carlo generatorsâ statistics for event simulation and generation in particle physics. Given the already high computational cost of simulation and the expected increase in data in the high-precision era of the LHC and at future colliders, such fast surrogate simulators are urgently needed. This contribution presents a status update on simulating particle showers in high granularity calorimeters for future colliders. Building on prior work using Generative Adversarial Networks (GANs), Wasserstein-GANs, and the information-theoretically motivated Bounded Information Bottleneck Autoencoder (BIB-AE), we further improve the fidelity of generated photon showers. The key to this improvement is a detailed understanding and optimisation of the latent space. The richer structure of hadronic showers compared to electromagnetic ones makes their precise modeling an important yet challenging problem. We present initial progress towards accurately simulating the core of hadronic showers in a highly granular scintillator calorimeter