In 2024 LHC managed to deliver more than 100/fb of integrated luminosity to ATLAS+CMS in a single year, with an average of 57 pileup interactions happening in the same bunch crossing, and thus challenging the CMS detector and jet reconstruction. We present the latest developments in jet calibration and performance for LHC Run3
The precision and reach of physics analyses at the LHC is often tied to the performance of hadronic object reconstruction & calibration, with any incremental gains in understanding & reduced uncertainties being impactful on ATLAS results. Recent refinements to the reconstruction and calibration procedures for jets & missing energy by the ATLAS collaboration has resulted in reduced...
Hadronic object reconstruction & classification is one of the most promising settings for cutting-edge machine learning and artificial intelligence algorithms at the LHC. In this contribution, highlights of ML/AI applications by ATLAS to QCD and boosted-object identification, MET reconstruction and other tasks will be presented.
Innovation in jet tagging techniques to identify quark flavours, gluons or boosted heavy particles (tau, W,Z,H,top) has been an important driver to maximally exploit the physics potential of LHC data, and remains an active area of study in CMS. In this talk we present latest algorithm developments and performance results.
Missing transverse momentum is a crucial experimental observable for many analyses of data from detectors at hadron colliders. In the standard model, missing transverse momentum originates from neutrinos. Moreover, beyond the standard model particles like dark matter candidates are also expected to leave the detector undetected. This talk presents a novel missing transverse momentum estimator...
The principal ATLAS calorimeter signals are clusters of topologically connected cell signals. These clusters do not only provide an energy and direction measurement, but also have sufficient shape and other structural information allowing to calibrate to individually calibrate them. The standard approach is to use multi-dimensional binned look-up tables to retrieve scale factors for this...
We present recent progress in CMS towards an improved implementation of the PF reconstruction with the use of machine learning.
We present the first application of graph neural networks using GravNet and object condensation to particle flow reconstruction at the International Linear Collider. By embedding both calorimeter hits and tracking information into a latent space, our deep learning model performs simultaneous particle clustering and energy regression. Charged tracks are treated as condensation anchors,...
The Lund jet plane is a representation of the emissions within a jet, where each point corresponds to an emission. Hard and soft emissions, as well as colinear and wide-angle emissions, correspond to different regions of the Lund plane and are populated differently by jets with different origins. This means the Lund plane can be used for jet tagging. We present previous studies done in ATLAS...
A muon collider combines high center-of-mass energy, clean collision environments, and compact designs into a tool for high energy physics. This study addresses the critical challenge of the beam-induced background (BIB), a byproduct of muon decay that complicates event reconstruction and impacts detector performance. We explore software-based solutions, including algorithms like SoftKiller...
The identity of dark matter (DM) is one of the most profound questions at the interface of particle physics and cosmology. Weakly interacting massive particles (WIMPs) are promising DM candidates that explain the observed relic density and are under investigation in direct and indirect searches. Within the context of R-parity conserving supersymmetric extensions of the standard model, the WIMP...
As the accuracy of experimental results increase in high energy physics, so too must the precision of Monte Carlo simulations. Currently, event generation at next to leading order (NLO) accuracy and beyond results in a number of negative weighted events. Not only are these unphysical, but they also drive up the computational load and can be pathological when used in machine learning analyses....
In hadron collider experiments, it is essential to accurately reconstruct particles from detector information in order to gain a deeper understanding of a various phenomena. In particular, since detectors such as ATLAS have limited spatial granularity in the calorimeter cell, it is challenging to reconstruct particles within jets.
To mitigate this difficulty, we are developing a Particle...
Particle flow (PFlow) is one of the key detector concepts of future Higgs factories. It went back to more than 15 years ago that a proposal of highly-granular calorimeters with PFlow algorithm giving almost twice better jet energy resolution than traditional calorimetry was published.
The expected performance has not significantly changed since then while the hardware studies have been...
Many modern jet clustering algorithms, for example, the anti-$k_T$ algorithm, were proposed after LEP had concluded. This poses a unique opportunity and challenge in order to analyze the archived $e^+e^-$ data from the LEP era. In this poster, we will discuss the methodologies to calibrate jets developed specifically for $e^+e^-$ collisions, as well as a discussion on jet observables that this...
A search for high-mass resonances decaying into a gluon, g, and two W bosons is presented. A Kaluza-Klein gluon, $g_{KK}$, decaying in cascade via a scalar radion R, $g_{KK} \to gR \to gWW$, is considered. The final state consists of three large-radius jets, two of which contain the products of hadronically decaying W bosons, and the third one the hadronization products of the gluon. The...
Splitting functions are the factorized forms of collinear dynamics in perturbative QCD, used to model complex parton showers. We compute the massive triple-collinear splitting kernels by layering scalar (semi-classical) interaction and fermionic interference terms, and compare to existing results for massive and massless splittings. This decomposition method enables systematic integration of...
This study investigates the performance of SoftKiller, a pileup mitigation algorithm, in high-pileup conditions using a Julia-based implementation. The SoftKiller algorithm aims to mitigate the effects of pileup by removing low-momentum particles through a process involving grid partitioning, cell sum computation, thresholding, soft removal, and clustering. The Julia implementation of...
In this talk, I will present our research on the substructure of jets containing heavy flavour. Our main goal is to better understand these jets from a theoretical perspective, using resummed perturbative techniques that are specially designed for jets coming from heavy quarks. In particular, we provide analytical predictions for several key jet substructure observables, including jet...
Energy-energy correlators (EECs) within high energy jets serve as a key experimentally accessible quantity to probe the scale and structure of the quark-gluon plasma (QGP) in relativistic heavy-ion collisions. The CMS Collaboration's first measurement of the modification to the EEC within single inclusive jets in Pb+Pb collisions relative to p+p collisions reveals a significant enhancement at...
Jet flavor tagging for linear Higgs factories (ILC, CLIC) has long been done with BDT-based algorithm. Stimulated from recent improvements in LHC experiments, the update has been done with DNN-based algorithm, namely Particle Transformer (ParT). It already shows great improvement of around factor 10 in background rejection for b and c tagging. It also enables to do strange tagging as well as...
The accurate identification of heavy-flavour jets is crucial for many aspects of the LHC physics program. However, assigning flavour to jets presents significant challenges, primarily due to potential sensitivity to infrared energy scales. We present the results of a recent study that evaluate jet algorithms designed to be infra-red and collinear safe and applicable in high-precision...
Accurate identification of jets that originate from heavy-flavor hadrons is pivotal for many ATLAS analyses, from Higgs-boson and top-quark measurements to searches for new physics. We present the newest heavy-flavor taggers from ATLAS, which introduces a full-transformer architecture tailored to the environment of Run 2 and Run 3.
The flavor tagging transformer processes low-level track,...
sPHENIX is the first newly constructed detector at a hadron collider in over a decade, featuring a compact design and a set of unique, purpose-built capabilities not previously available at RHIC. The sPHENIX heavy-flavor program at RHIC is designed to address fundamental questions about the strongly interacting Quark-Gluon Plasma (QGP) using jets originating from heavy-quarks as precision...
Heavy flavor (charm and bottom) production is a unique probe to test the perturbative Quantum Chromodynamics (pQCD) and study the transport properties of nuclear media. Heavy flavor signal searching is one of the most challenging measurements in collider experiments due to their ultra-low production rate and extensive backgrounds. The brand new sPHENIX experiment at the Relativistic Heavy Ion...
The mass of heavy quarks modifies the radiation pattern of heavy-quark jets in comparison to their light quark counterparts, since the heavy quark mass effectively regularizes the soft and collinear divergences that would normally dominate the partonic cascade formation. This leads to the depletion of collinear gluon emissions relative to the heavy quark, an effect known as the dead cone...
The fragmentation process in QCD remains an elusive mystery. Energy Correlators, which are correlation functions of energy flow, provide a novel new probe into the dynamics of the QCD phase transition and secondly provide a precision technique for the experimental measurement of fundamental parameters in QCD: i.e. the strong coupling constant. In this talk, we will describe extensions of these...
Jets are powerful probes used to improve our understanding of the strong force at short distances. The radiation pattern of jets can be visualized via the Lund jet plane, a two-dimensional representation of the phase space of intrajet emissions using the splitting angle and the relative transverse momentum of the emission relative to the emitter. The Lund jet plane allows for the separation of...
n this talk, we present the first measurement of jet substructure modification in the QGP medium with fully reconstructed jets using $\Delta j$ observable, which quantifies the distance between two types of jet axes constructed from the same jet constituents. The E-scheme anti-$k_T$ and Winner-Takes-All axes are employed, providing different sensitivities to soft and semi-hard medium-induced...
Precision studies of jets and their substructure at the LHC require a robust theoretical description for anti-$k_t$ jet production. For small-radius jets, the cross section can be factorized into parton distribution functions, a hard function, and a jet function that encodes the jet clustering effects. We present the two-loop calculation of this jet function and uncover previously missing...
Jet substructure observables are an effective probe of QCD in many environments. In the vacuum of pp collisions, they simultaneously probe the weakly coupled properties of parton showers and the strongly coupled phenomena of hadronisation. In the presence of the deconfined QCD medium, jet substructure observables provide a multi-scale tool to test the scale-dependent evolution of the QGP...
The experimental study of energy-energy correlators is rapidly emerging as a powerful tool for understanding the QCD dynamics that govern jet formation at the LHC. These observables have a particularly close relationship with the operators in the underlying field theory, allowing for strong theory-experiment correspondences and relatively straightforward theoretical interpretations of...
N-point energy correlators have recently gained prominence in the field of high energy particle and nuclear physics due to features that make the observable a unique probe of multi-scale QCD evolution. Several experimental collaborations have either measured the 2-point energy-energy correlator (EEC), an observable that quantifies the energy product weighted particle pairs within a jet or...
One of the fundamental challenges in studying QCD and jet physics is the different effective degrees of freedom at different energy scales. The hard scattering processes which form jets, as well as the jet evolution, are described in terms of weakly-interacting partons, whereas the particles we observe in our detectors and do measurements on are free hadrons. Theoretically, this means one does...
The jet mass of W bosons decaying to a quark-antiquark pair is measured in W+jet events from proton-proton collisions in the LHC at a center-of-mass energy of $\sqrt{s}$ = 13 TeV. W bosons with large transverse momentum (boost) produce strongly collimated decay products reconstructed as single large-radius jets. Jets initiated by W bosons with a characteristic two-prong substructure are...
(contribution via zoom)
The production of W/Z bosons in association with jets at the LHC provides an important test of perturbative QCD. In this talk, differential cross-sections of W boson production with at least one jet are measured for events in which the W boson decays in the electron or muon channels, and compared to predictions at next-to-next-to-leading-order (NNLO), with an...
Measuring the Higgs boson production at high transverse momentum pT is a core component of the Higgs boson physics program at the LHC. The high-pT regime poses challenges to precise theoretical predictions and is a sensitive probe for indirect searches of new physics. This talk will review recent results of the CMS experiment in the search for Higgs boson production with high Lorentz boost.
A simultaneous measurement of twenty-five jet substructure observables is presented using large-radius jets with high transverse momentum from proton-proton collisions at $\sqrt{s}=13$ TeV. The measurement is carried out on QCD dijet events and $t\overline{t}$ events enriched in boosted, hadronic decays of W bosons and top quarks. The three data samples consist of jets with one, two, and three...
We present a study of the density of emissions in the Lund Jet Plane for hadronic decays of boosted top quarks. We consider the case where all top quark decay products are reconstructed in a single large jet. The three-prong decay of the top quark offers a rich substructure where the two quarks from the W decay are not color-connected to the b quark, and all three quarks originate from the...
High charged-particle multiplicity event has been a central focus in the study of collective behavior across both large and small collision systems. A previous measurement of two-particle angular correlations in $e^+e^-$ collisions at center-of-mass energies up to $\sqrt{s} = 209,\mathrm{GeV}$, using LEP-II data, revealed intriguing discrepancies with Monte Carlo predictions at high...
State-of-the-art machine learning models in particle physics, such as PELICAN [1] and Particle Transformer [2], exhibit disadvantageous $\mathcal{O}(N^2)$ scaling with the multiplicity $N$ of the jets. Fundamentally, this has to do with the tendency for highly expressive models to involve complicated permutation-equivariant layers to model pairwise interactions. Similar limitations arise in...
Modern ML-based taggers have set new benchmarks for jet classification tasks at the LHC, surpassing traditional algorithms in performance. However, their opaque decision-making processes pose challenges for interpretability. In this work, we investigate what a low-level tagger learns when trained on quark-gluon discrimination. We identify a small set of learned latent features that correlate...
Fixed-order perturbative calculations for physical cross sections can suffer from non-physical artifacts: they can be non-finite, non-positive, non-normalizable, and susceptible to large logarithmic corrections. We propose a framework that, given a fixed-order perturbative expression for an observable to some finite order in $\alpha$, will ``resum'' the expression in a way that is guaranteed...
We propose $w_i f_i$ ensembles, a novel framework to obtain asymptotic frequentist uncertainties on density ratios in the context of neural ratio estimation. In the case where the density ratio of interest is a likelihood ratio conditioned on parameters, for example a likelihood ratio of collider events conditioned on parameters of nature, it can be used to perform simulation-based inference...
With the increasing size of the machine learning (ML) model and vast datasets, the foundation model has transformed how we apply ML to solve real-world problems. Multimodal language models like chatGPT and Llama have expanded their capability to specialized tasks with common pre-train. Similarly, in high-energy physics (HEP), common tasks in the analysis face recurring challenges that demand...
Precise, high-energy $e^{+}e^{-}$ data remain essential for a global understanding of particle physics. Despite decades since the end of the Large Electron-Positron Collider (LEP), such data continue to play a central role in precision measurements and the tuning of phenomenological models in parton shower Monte Carlo (MC) simulations. One particularly important observable is thrust, which...
(contribution via Zoom)
The practice of collider physics typically involves
the marginalization of multi-dimensional collider data to uni-dimensional observables relevant for some physics task. In many cases, such as discrimination or anomaly detection, the observable can be arbitrarily complicated, such as the output of a neural network. However, for precision measurements, the...
In recent years, there has been a resurgence of interest in energy-energy correlators (EECs) for the study of hadronic collisions at both the LHC and RHIC ranging from small to large systems. Measurements of EECs of particles within jets offer a clear separation of scales that is useful for studying both perturbative and non-perturbative QCD in the collinear limit as well as the transition...
We present a measurement of thrust, energy-energy correlators, and two-particle angular correlations of charged particles in $e^+e^-$ ) collisions at center-of-mass energies up to $\sqrt{s} = 209\,\mathrm{GeV}$, using newly released open data access from the DELPHI experiment at LEP-I and -II. The thrust and energy-energy correlator, measured with unprecedented resolution and precision, are...
Searches for new resonances in di-boson (VV, VH, HH, where V = W, Z) and tri-boson final states, with the CMS detector are presented. The analyses are optimised for high sensitivity over a large range in resonance mass. Jet substructure techniques are used to identify hadronic decays of highly-boosted W, Z, and H bosons. A statistical combination of these searches provides the most stringent...
In this talk, we present our extension of the concept of maximal quantum entanglement from proton structure to jet fragmentation in proton-proton collisions, establishing a connection between jet fragmentation functions and charged hadron multiplicity [1]. This relationship is tested using ATLAS data from the Large Hadron Collider, showing excellent agreement. As the first study to apply...
We study the QCD scaling behavior of the small-angle Energy-Energy Correlator (EEC), focusing on the transition between its perturbative pre-confinement and non-perturbative post-confinement regimes. Applying the light-ray Operator Product Expansion (OPE), we develop a formalism that describes the scaling of the EEC with the input energy
$Q$ in the transition and the post-confinement region,...
This talk presents recent advancements in the angular-ordered parton shower algorithm, extending Beyond the Standard Model (BSM) radiations on top of the existing Standard Model (SM) only algorithm. Capitalising on the fact that shower kinematics are fully determined by the spins of involved particles, helicity-dependent splitting functions for all viable combinations of scalar bosons,...
This talk presents the latest results from searches for signatures targeting hidden valley models performed in proton-proton collision data recorded by CMS. These models propose new strong-like forces, sometimes called "dark QCD" which lead to composite dark matter in the form of "dark hadrons" that are difficult to search for and evade the usual collider dark matter searches. Evidence of...
Many theories beyond the Standard Model (SM) have been proposed to address several of the SM shortcomings. Some of these beyond-the-SM extensions predict new particles or interactions directly accessible at the LHC, but which would leave unconventional signatures in the ATLAS detector. These unconventional signatures require special techniques and reconstruction algorithms to be developed,...
