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Machine learning reweighting of MC parameters and MC samples of top quark production in CMS
No full textParticle physics relies on Monte Carlo (MC) event generators for theory-data comparison, necessitating several samples to address theoretical systematic uncertainties at a high computational cost. The MC statistic becomes a limiting factor and the significant computational cost a bottleneck in most physics analyses. In these proceedings, the Deep neural network using Classification for Tuning and Reweighting (DCTR) is used to reweight simulations to different models or model parameters by using the full event kinematic information. This methodology avoids the need for simulating the detector response multiple times by incorporating the relevant variations in a single sample. In these proceedings, DCTR is evaluated for the reweighting of two systematic uncertainties in MC simulations of top quark pair production in the CMS experiment. Additionally, it is investigated for reweighting a next-to-leading-order generator to a next-to-next-to-leading-order generator for top quark pair production
Capturing ultrafast molecular motions and lattice dynamics in spin crossover film using femtosecond diffraction methods
No full textA comprehensive insight into ultrafast dynamics of photo-switchable materials is desired for efficient control of material properties through light excitation. Here, we study a polycrystalline spin crossover thin film as a prototypical example and reveal the sequential photo-switching dynamics, from local molecular rearrangement to global lattice deformation. On the earliest femtosecond timescale, the local molecular structural rearrangement occurs within a constant unit-cell volume through a two-step process, involving initial Fe−ligand bond elongation followed by ligand rotation. The highly-oriented structure of the nanocrystalline films and the experimental geometry enables resolving the full anisotropic lattice structural dynamics in and out of the sample plane separately. While both molecular switching and lattice heating influence lattice volume, they exert varying degrees of impact at disparate time scales following photoexcitation. This study highlights the opportunities provided by Mega-electron-volt electron and X-ray free electron laser to advance the understanding of ultrafast dynamics of photo-switchable materials
Implementation of the Matrix Element Method and a Jet Clustering Algorithm with Machine Learning at Future Higgs Factories
No full textA top priority of future collider programs is to measure the value of the Higgs self-coupling λ. Through double Higgs production (ZHH), this is possible by direct measurement at lepton col-liders. However, both reconstruction and analysis face challenges due to the high number of jets, misclustering effects in the jet clustering procedure and separation of the signal from irreducible backgrounds (ZZH). In this thesis, approaches and solutions for both are presented. First, a jet clustering algorithm based on Graph Neural Networks and Spectral Clustering is presented and shown to produce nearly identical as the benchmark (Durham algorithm). Then, for the analysis, multiple multivariate methods are explored, such as likelihood-ratio testing with the Matrix-Element-Method and direct classification using machine learning models including transformers and Deep Sets. The best results give a final average precision and AUROC for separating ZHH and ZZH events correctly of 67% and 0.78, respectively
Searches for the rare tWZ and tWγ processes at the LHC using machine learning techniques
No full textThis thesis work presents the first searches and the first evidences for the and processes at the LHC with the CMS experiment. The analyses employ proton-proton collision data corresponding to an integrated luminosity of 138 fb collected during Run 2 of the LHC between 2016 and 2018. Purpose-built Machine Learning algorithms are developed in these searches in order to discriminate the rare signal processes from the large background, consisting mostly of production processes of top quark pairs in association with a boson or a photon. Additionally, this thesis describes the treatments used to describe the modeling and simulation of the and production process
Radiative transitions in irradiated MgAlO spinel crystal
No full textadiative transitions in MgAl2O4 spinel single crystal were investigated after irradiation with He+ ions of fluence ∼1017 particles/cm2. Photoluminescence (PL), PL excitation spectra and PL decay curves were measured at cryogenic temperatures of 8 K. It is shown that PL decay kinetics of 5 eV (250 nm) and 3 eV (420 nm) bands are similar because of the common excited state. Furthermore, after irradiation PL band at ∼5 eV preserved characteristic behaviour of the donor-acceptor pair transitions. The PL channels involve electronic transitions of antisite defects, MgAl (shallow acceptor) and AlMg (shallow donor), and oxygen vacancy VO (deep donor), while AlMg served an intermediate of the electronic excitation channel. The intense emissions were assigned to VO•∗ → VO• (3 eV) and VO•∗ → MgAl× (5 eV), which involve respectively energy and energy-electron transfer. Participation of the doubly-ionized oxygen vacancy VO•• in the energy/electron transfer is suggested. The obtained data enabled a generalised scheme of electronic transitions in MgAl2O4 spinel in presence of intrinsic defects
Introduction to Statistics and Data Analysis for Physicists
No full textThe tools of statistical analysis for experiments in modern physical applications are increasingly sophisticated and specific tools are needed to reliably extract results from complex data. This textbook thus presents a comprehensive treatment of the topic for the practicing physicist, focusing less on mathematical foundations but appealing to intuitive techniques with a large number of examples.This fourth edition is greatly expanded with new sub-topics not covered in standard textbooks. We begin with fundamental probability concepts and measurement errors, continuing to the indispensable Monte Carlo simulation. Likelihood and its underlying likelihood principle are explored, serving as bases for the sections on parameter inference and the treatment of distorted data. Topics like hypothesis testing, the statistics of weighted events, the elimination of nuisance parameters, and deconvolution are updated with new developments. Final chapters introduce other advanced techniques such as statistical learning and bootstrap sampling.Developed and greatly expanded from a graduate course at the University of Siegen, this book serves as an essential resource for all graduate students and researchers seeking a rigorous foundation in statistical methods for experimental physics, especially those in nuclear, particle and astrophysics
Chirality in the Kagome Metal CsVSb
No full textUsing x-ray photoelectron diffraction (XPD) and angle-resolved photoemission spectroscopy, we study photoemission intensity changes related to changes in the geometric and electronic structure in the kagome metal CsVSb upon transition to an unconventional charge density wave (CDW) state. The XPD patterns reveal the presence of a chiral atomic structure in the CDW phase. Furthermore, using circularly polarized x-rays, we have found a pronounced nontrivial circular dichroism in the angular distribution of the valence band photoemission in the CDW phase, indicating a chirality of the electronic structure. This observation is consistent with the proposed orbital loop current order. In view of a negligible spontaneous Kerr signal in recent magneto-optical studies, the results suggest an antiferromagnetic coupling of the orbital magnetic moments along the axis. While the inherent structural chirality may also induce circular dichroism, the observed asymmetry values seem to be too large in the case of the weak structural distortions caused by the CDW
HOPS/CORVET tethering complexes are critical for endocytosis and protein trafficking to invasion related organelles in malaria parasites
No full textThe tethering complexes HOPS/CORVET are central for vesicular fusion through the eukaryotic endolysosomal system, but the functions of these complexes in the intracellular development of malaria parasites are still unknown. Here we show that the HOPS/CORVET core subunits are critical for the intracellular proliferation of the malaria parasite Plasmodium falciparum. We demonstrate that HOPS/CORVET are required for parasite endocytosis and host cell cytosol uptake, as early functional depletion of the complex led to developmental arrest and accumulation of endosomes that failed to fuse to the digestive vacuole membrane. Late depletion of the core HOPS/CORVET subunits led to a severe defect in merozoite invasion as a result of the mistargeting of proteins destined to the apical secretory organelles, the rhoptries and micronemes. Ultrastructure-expansion microscopy revealed a reduced rhoptry volume and the accumulation of numerous vesicles in HOPS/CORVET deficient schizonts, further supporting a role of HOPS/CORVET in post-Golgi protein cargo trafficking to the invasion related organelles. Hence, malaria parasites have repurposed HOPS/CORVET to perform dual functions across the intraerythrocytic cycle, consistent with a canonical endocytic pathway for delivery of host cell material to the digestive vacuole in trophozoite stages and a parasite specific role in trafficking of protein cargo to the apical organelles required for invasion in schizont stages
Conformational signatures induced by ubiquitin modification in the amyloid-forming tau repeat domain
Get PDFPosttranslational modifications can critically affect conformational changes of amyloid-forming proteins. Ubiquitination of the microtubule-associated tau protein, an intrinsically disordered biomolecule, has been proposed to influence the formation of filamentous deposits in neurodegenerative conditions. Given the reported link between aggregation propensity and intrinsic structural preferences (e.g., transient extended structural motifs or tertiary contacts) in disordered proteins, we sought to explore the conformational landscape of ubiquitinated tau. Exploiting selective conjugation reactions, we produced single- and double-monoubiquitinated protein samples. Next, we examined the ubiquitinated species from different standpoints using NMR spectroscopy, small-angle X-ray scattering experiments, and native ion mobility–mass spectrometry (IM–MS). Moreover, we obtained atomistic representations of the conformational ensembles via scaled MD calculations, consistent with the experimental data. Modifying the repeat domain of tau with ubiquitin had a limited effect on secondary structure propensities and local mobility of distal regions. Instead, ubiquitination enhanced the compaction of the conformational ensemble, with the effect modulated by the site and the number of modifications. Native IM–MS patterns pinpointed similarities and differences between distinct tau proteoforms. It emerges that ubiquitination exerts a position-specific influence on the conformational distribution of tau molecules. This study reveals the unique conformational features of ubiquitinated forms of tau and points to their potential impact on aggregation and phase separation propensities, offering clues for a better understanding of disease-related structural alterations