In particle physics, Monte Carlo (MC) event generators are needed to compare theory to the measured data. Many MC samples have to be generated to account for theoretical systematic uncertainties, at a significant computational cost. Therefore, the MC statistic becomes a limiting factor for most measurements and the significant computational cost of these programs a bottleneck in most physics...
The task of reconstructing physical observables from recorded experimental data in hadron collider events is a common challenge in LHC data analysis. Experimental measurements, such as hits in tracking detectors and signals in calorimeters, are combined into particle-flow objects, such as jets, muons, electrons, and missing transverse energy. However, reconstructing key observables related to...
The Cabibbo Kobayashi Maskawa (CKM) matrix describes the flavor-changing quark interactions. Vts is the matrix element that describes the coupling between the top and strange quark, has not been directly measured. A direct measurement of |Vts| can be performed by identifying the strange jets from top decays. The strange jet tagging problem is challenging due to the similarity of strange jets...
In this work, we present a study on how machine learning (ML) can be used to enhance charged particle tracking algorithms. In particular, we focus on the line-segment-based tracking (LST) algorithm that we have designed to be naturally parallelized and vectorized on modern processors. LST has been developed specifically for the Compact Muon Solenoid (CMS) Experiment at the LHC, towards the...
We present a novel approach to solving combinatorial assignment problems in particle physics without the need to introduce prior knowledge or assumptions about the particles' decay. The correct assignment of decay products to parent particles is achieved in a model-agnostic fashion by introducing a novel neural network architecture, Passwd-ABC, which combines a custom layer based on attention...
Tracking of charged particles in dense environments, especially in the core of high transverse-momentum ($p_T$) jets, presents a growing challenge with increasing LHC luminosity. Despite the CMS phase-1 pixel detector upgrade, and dedicated cluster splitting and pattern recognition algorithms like JetCore, there is still significant room for improvement. Limiting the computation time for track...
Dielectrons are an exceptional tool to study the evolution of the medium created in heavy-ion collisions. In central collisions, the energy densities are sufficient to create a quark-gluon plasma (QGP). At LHC energies, the dominant background process for the measurements of thermal e$^{+}$e$^{-}$ pairs originating from the QGP are correlated HF hadron decays which dominate the dielectron...
The search for rare New Physics signals is one of the main challenges that are addressed in LHC experiments. Classical search strategies rely on signal hypothesis and simulation to optimize the sensitivity of an analysis. However, relying on hypothesis and simulation has drawbacks. To address this problem, I propose a model independent strategy for heavy resonance searches.
This...
The identification of electrons plays an important role in a large fraction of the physics analyses performed at ATLAS. An improved electron identification algorithm is presented that is based on a convolutional neural network (CNN). The CNN utilizes the images of the deposited energy in the calorimeter cells around the reconstructed electron candidates for each of the electromagnetic and...
Particle identification (PID) plays a pivotal role in numerous measurements performed by the ALICE Collaboration. Various ALICE detectors offer PID information through complementary experimental techniques. The former ALICE Inner Tracking System 1 (ITS1) provided PID information by measuring the specific energy loss of low-momentum charged particles during LHC Run 1 and Run 2. The upgraded ITS...
Novel decorrelation method using Convex Neural Optimal Transport Solvers (Cnots) that is able to decorrelate a continuous feature space against protected attributes with optimal transport. We demonstrate how well it performs in the context of jet classification in high energy physics, where classifier scores are desired to be decorrelated from the mass of a jet.
One of the most interesting channels to probe theories beyond the Standard Model at LHC, is the production of a new massive particle, that decays into pairs of Higgs Bosons which, in turn, decay into a pair of b-quarks and a pair of tau leptons. A fundamental discriminant variable to separate HH signal from the backgrounds is the invariant mass of the di-tau system, which can be reconstructed...
Progress in the theoretical understanding of parton branching dynamics that occurs within an expanding QGP relies on detailed and fair comparisons with experimental data for reconstructed jets. Such validation is only meaningful when the computed object, be it analitically or via event generation, accounts for the complexity of experimentally reconstructed jets. The reconstruction of jets in...
Proton therapy is highly sensitive to range uncertainties due to the nature of the dose deposition of charged particles. To ensure treatment quality, range verification methods can be used to verify that the individual spots in a pencil beam scanning treatment fraction match the treatment plan. We employ uncertainty-aware deep neural networks to predict the Bragg peak depth in an...
Heavy flavour jets underpin a large part of the ATLAS physics programme, such as analyses of Higgs boson decays to quarks and super-symmetry searches with b-jets. The algorithms for identifying jets originating from b- and c-quarks are instrumental in these efforts, with the recently introduced GN2 model [1] showing remarkable improvements in tagging efficiency. Given its complexity and data...
Deep learning, especially graph neural networks, significantly improved tracking performances in modern particle detectors while reducing runtimes compared to previous state of the art approaches. However, training neural networks requires significant amount of labeled data, usually acquired by performing complex particle simulations. We present first studies of leveraging deep reinforcement...
Addressing the challenge of Out-of-Distribution (OOD) multi-set generation, we introduce YonedaVAE, a novel equivariant deep generative model inspired by Category Theory, motivating the Yoneda-Pooling mechanism. This approach presents a learnable Yoneda Embedding to encode the relationships between objects in a category, providing a dynamic and generalizable representation of complex...
Alpha Magnetic Spectrometer (AMS-02) is a precision high-energy cosmic-ray experiment on the ISS operating since 2011 and has collected more than 228 billion particles. Among them, positrons are important to understand the particle nature of dark matter. Separating the positrons from cosmic background protons is challenging above 1 TeV. Therefore, we use state-of-the-art convolutional and...
We propose a differentiable vertex fitting algorithm that can be used for secondary vertex fitting, and that can be seamlessly integrated into neural networks for jet flavour tagging. Vertex fitting is formulated as an optimization problem where gradients of the optimized solution vertex are defined through implicit differentiation and can be passed to upstream or downstream neural network...
During the data-taking campaigns Run 1 and Run 2 of the Large Hadron Collider (LHC), the ALICE collaboration collected a large amount of proton-proton (pp) collisions across a variety of center-of-mass energies ($\sqrt{s\,}$). This extensive dataset is well suited to study the energy dependence of particle production. Deep neural networks (DNNs) provide a powerful regression tool to capture...
In High Energy Physics, detailed and time-consuming simulations are used for particle interactions with detectors. To bypass these simulations with a generative model, the generation of large point clouds in a short time is required, while the complex dependencies between the particles must be correctly modelled. Particle showers are inherently tree-based processes, as each particle is...
The Data-Directed paradigm (DDP) is a search strategy for efficiently probing new physics in a large number of spectra with smoothly-falling SM backgrounds. Unlike the traditional analysis strategy, DDP avoids the need for a simulated or functional-form based background estimate by directly predicting the statistical significance using a convolutional neural network trained to regress the...
Hadronization is a critical step in the simulation of high-energy particle and nuclear physics experiments. As there is no first principles understanding of this process, physically-inspired hadronization models have a large number of parameters that are fit to data. We propose an alternative approach that uses deep generative models, which are a natural replacement for classical techniques,...
A major task in particle physics is the measurement of rare signal processes. These measurements are highly dependent on the classification accuracy of these events in relation to the huge background of other Standard Model processes. Reducing the background by a few tens of percent with the same signal efficiency can already increase the sensitivity considerably.
This study demonstrates...
Accurate knowledge of longitudinal beam parameters is essential for optimizing the performance and operational efficiency of particle accelerators like the Large Hadron Collider (LHC). However, conventional methods to determine them, such as fitting techniques and tracking-based longitudinal tomography, are time-consuming and limited to analyzing data from a few bunches only. To address this,...
The energy and mass measurements of jets are crucial tasks for the Large Hadron Collider experiments. This paper presents a new calibration method to simultaneously calibrate these quantities for large-radius jets measured with the ATLAS detector using a deep neural network (DNN). To address the specificities of the calibration problem, special loss functions and training procedures are...
A search for long-lived heavy neutral leptons (HNLs) is presented, which considers the hadronic final state and coupling scenarios involving all three lepton generations in the 2-20 GeV HNL mass range for the first time. A central feature of the analysis is a novel jet tagger, based on a deep neural network (DNN), that has been developed to identify displaced jets from an HNL decay using...
Track reconstruction is a crucial part of High Energy Physics (HEP) experiments. Traditional methods for the task scale poorly, making machine learning and deep learning appealing alternatives. Following the success of transformers in the field of language processing, we investigate the feasibility of training a Transformer to translate detector signals into track parameters. We study and...
Beyond the Standard Model (BSM) sources of CP violation are one of the required ingredients for solving the matter-antimatter puzzle. Simulation-based inference methods hold the promise of allowing the estimation of optimal observables or likelihood ratios without requiring approximations (e.g. of the effect of shower and hadronization), ensuring a high sample efficiency through the use of...
Simulated events are key ingredients for almost all high-energy physics analyses. However, imperfections in the configuration of the simulation often result in mis-modelling and lead to discrepancies between data and simulation. Such mis-modelling often must be taken into account by correction factors accompanied by systematical uncertainties, that can compromise the sensitivity of...
A particularly interesting application of autoencoders (AE) for High Energy Physics is their use as anomaly detection (AD) algorithms to perform a signal-agnostic search for new physics. This is achieved by training AEs on standard model physics and tagging potential new physics events as anomalies. The use of an AE as an AD algorithm relies on the assumption that the network better...
Semivisible jets are are a novel signature arising in Hidden Valley (HV) extensions of the SM with a confining interaction [1]. Originating from a double shower and hadronization process and containing undetectable dark bound states, semivisible jets are expected to have a substantially different radiation pattern compared to SM jets.
Unsupervised...
Machine learning based jet tagging techniques have greatly enhanced the sensitivity of measurements and searches involving boosted final states at the LHC. However, differences between the Monte-Carlo simulations used for training and data lead to systematic uncertainties on tagger performance. This talk presents the performance of boosted top and W boson taggers when applied on data sets...
In this study, we focused on inferring BSM models and their parameters from the kinematic distributions of collider signals via an n-channel 1D-Convolutional Neural Network (1D-CNN). As new physics may influence two or more observables, a 2D-CNN approach might not always be the best option. Alternatively, one can use a simple MLP with any number of observables via an event-by-event approach....
We introduce a new approach using generative machine learning to sample meaningful generator-level events given reconstructed events in the CMS detector. Our method combines Transformers and Normalizing Flows to tackle the challenge of integrating the Matrix Element Method with importance sampling. We propose using a Transformer network to analyze the full reconstructed event and extract...
In this analysis, we apply modern machine learning techniques to the $H\rightarrow WW^* \rightarrow e \nu \mu \nu$ decay channel using data from the ATLAS detector collected during Run-2 of the LHC to precisely measure the total cross sections of both gluon-gluon Fusion (ggF) and Vector Boson Fusion (VBF) Higgs production modes. The detailed results can be found in the 2023 publication...
We propose a new method based on machine learning to play the devil’s advocate and investigate the impact of unknown systematic effects in a quantitative way. This method proceeds by reversing the measurement process and using the physics results to interpret systematic effects under the Standard Model hypothesis. We explore this idea with two alternative approaches, one relies on a...
We show that employing a sophisticated neural network emulation of QCD multijet matrix elements based on dipole factorisation can lead to a drastic acceleration of unweighted event generation in high-multiplicity LHC production processes. We incorporate these emulations as fast and accurate surrogates in a two-stage rejection sampling algorithm within the SHERPA Monte Carlo that yields...
The Fair Universe project is building a large-compute-scale AI ecosystem for sharing datasets, training large models and hosting challenges and benchmarks. Furthermore, the project is exploiting this ecosystem for an AI challenge series focused on minimizing the effects of systematic uncertainties in High-Energy Physics (HEP), and on predicting accurate confidence intervals. This talk will...
The usage of modern ML techniques to automate the search for anomalies in collider physics is a very active and prolific field. Typical cases are the search for signatures of physics beyond the Standard Model and the identification of problems in the detector systems that would lead to bad-quality data, unusable for physics data analysis. We are interested in the second type of task, which can...
Self-Supervised Learning (SSL) is at the core of training modern large ML models, providing a scheme for learning powerful representations in base models that can be used in a variety of downstream tasks. However, SSL training strategies must be adapted to the type of training data, thus driving the question: what are powerful SSL strategies for collider physics data? In the talk, we present a...
Full statistical models encapsulate the complete information of an experimental result, including the likelihood function given observed data. Since a few years ago ATLAS started publishing statistical models that can be reused via the pyhf framework; a major step towards fully publishing LHC results. In the case of fast Simplified Model Spectra based reinterpretation we are often only...
We present an end-to-end reconstruction algorithm for highly granular calorimeters that includes track information to aid the reconstruction of charged particles. The algorithm starts from calorimeter hits and reconstructed tracks, and outputs a coordinate transformation in which all shower objects are well separated from each other, and in which clustering becomes trivial. Shower properties...
The Bert pretraining paradigm has proven to be highly effective in many domains including natural language processing, image processing and biology. To apply the Bert paradigm the data needs to be described as a set of tokens, and each token needs to be labelled. To date the Bert paradigm has not been explored in the context of HEP. The samples that form the data used in HEP can be described...
Most searches at the LHC employ an analysis pipeline consisting of various discrete components, each individually optimized and later combined to provide relevant features used to discriminate SM background from potential signal. These are typically high-level features constructed from particle four-momenta. However, the combination of individually optimized tasks doesn't guarantee an optimal...
We have been studying the use of deep neural networks (DNNs) to identify and locate primary vertices (PVs) in proton-proton collisions at the LHC. Earlier work focused on finding primary vertices in simulated LHCb data using a hybrid approach that started with kernel density estimators (KDEs) derived from the ensemble of charged track parameters heuristically and predicted “target histogram”...
