Hadronic Jets Research Articles

Exposing a dual-readout fibre calorimeter to electron beams, in preparation for HiDRa: High-resolution calorimeter for [formula omitted] colliders

Among the proposed accelerators for the post-LHC era are the Future Circular Collider (FCC) and the Circular Electron–Positron Collider (CEPC). Both projects would take advantage of the clean environment and low radiation damage of electron–positron collisions, providing the highest precision studies of electroweak and Higgs physics. The relatively high branching fraction of W, Z and Higgs bosons into hadronic jets makes the precise measurements of these objects an essential aspect on detector development for experiments at future collider facilities. One of the most promising calorimetry techniques for improved hadron energy reconstruction is the dual-readout method, which exploits signals from two different physics processes to correct for the fem of hadron showers, therefore boosting the standalone calorimeter performance. The usage of compact photosensors (e.g. Silicon PhotoMultipliers) for the readout enables a very fine segmentation, opening to particle-flow and advanced neural networks software reconstruction of events. In this contribution, the results of testing a small-scale dual-readout calorimeter prototype, characterised by a mixed PMT and SiPM readout solution, with an electron beam at the CERN SPS facility in the energy range [10, 120] GeV are presented. It follows the description of a larger prototype of the same type, currently under construction in the context of the INFN HiDRa project, that will be large enough to fully contain hadron showers. The design, construction technique and expected performance, as estimated through a Geant4 simulation parameterised on the previous prototype, are presented.

Calibration of a soft secondary vertex tagger using proton-proton collisions at s=13 TeV with the ATLAS detector

Several processes studied by the ATLAS experiment at the Large Hadron Collider produce low-momentum b-flavored hadrons in the final state. This paper describes the calibration of a dedicated tagging algorithm that identifies b-flavored hadrons outside of hadronic jets by reconstructing the soft secondary vertices originating from their decays. The calibration is based on a proton-proton collision dataset at a center-of-mass energy of 13 TeV corresponding to an integrated luminosity of 140 fb−1. Scale factors used to correct the algorithm’s performance in simulated events are extracted for the b-tagging efficiency and the mistag rate of the algorithm using a data sample enriched in tt¯ events. Several orthogonal measurement regions are defined, binned as a function of the multiplicities of soft secondary vertices and jets containing a b-flavored hadron in the event. The mistag rate scale factors are estimated separately for events with low and high average numbers of interactions per bunch crossing. The results, which are derived from events with low missing transverse momentum, are successfully validated in a phase space characterized by high missing transverse momentum and therefore are applicable to new physics searches carried out in either phase space regime. © 2024 CERN, for the ATLAS Collaboration 2024 CERN

Measurement of Energy Correlators inside Jets and Determination of the Strong Coupling α_{S}(m_{Z}).

Energy correlators that describe energy-weighted distances between two or three particles in a hadronic jet are measured using an event sample of sqrt[s]=13 TeV proton-proton collisions collected by the CMS experiment and corresponding to an integrated luminosity of 36.3 fb^{-1}. The measured distributions are consistent with the trends in the simulation that reveal two key features of the strong interaction: confinement and asymptotic freedom. By comparing the ratio of the measured three- and two-particle energy correlator distributions with theoretical calculations that resum collinear emissions at approximate next-to-next-to-leading-logarithmic accuracy matched to a next-to-leading-order calculation, the strong coupling is determined at the Z boson mass: α_{S}(m_{Z})=0.1229_{-0.0050}^{+0.0040}, the most precise α_{S}(m_{Z}) value obtained using jet substructure observables.

Search for Narrow Trijet Resonances in Proton-Proton Collisions at sqrt[s]=13 TeV.

The first search for singly produced narrow resonances decaying to three well-separated hadronic jets is presented. The search uses proton-proton collision data corresponding to an integrated luminosity of 138 fb^{-1} at sqrt[s]=13 TeV, collected at the CERN LHC. No significant deviations from the background predictions are observed between 1.75 and 9.00TeV. The results provide the first mass limits on a right-handed boson Z_{R} decaying to three gluons and on an excited quark decaying via a vector boson to three quarks, as well as updated limits on a Kaluza-Klein gluon decaying via a radion to three gluons.

ILC sensitivity for leptophilic scalar dark matter

We explore the viability of detecting a leptophilic scalar dark matter (DM) at the International Linear Collider (ILC) in a simplified model approach. We present the constraints on the couplings of scalar DM with the standard model fermions ensuing from the relic density bounds deduced from the 2018 Planck data. We, then, present the reach of the ILC in terms of Λ, the scale of the effective theory, by performing a detailed analysis for the Z associated DM pair production (i.e. e + e − → 2 jets + ET , e + e − → μ + μ − + ET and e + e − → e + e − + ET ). We present the results for various run scenarios as 3σ contours in the m ϕ − Λ plane. We also analyze the effect of beam polarization on the sensitivity of this search. We find that for the process with two hadronic jets in the final state, ILC can probe Λ up to 1.76 TeV for s=1 TeV that can further enhance to 1.99 TeV, after the inclusion of polarization effects.

New metric improving Bayesian calibration of a multistage approach studying hadron and inclusive jet suppression

We study parton energy-momentum exchange with the quark gluon plasma (QGP) within a multistage approach composed of in-medium Dokshitzer-Gribov-Lipatov-Altarelli-Parisi evolution at high virtuality, and (linearized) Boltzmann transport formalism at lower virtuality. This multistage simulation is then calibrated in comparison with high-pT charged hadrons, D mesons, and the inclusive jet nuclear modification factors, using Bayesian model-to-data comparison, to extract the virtuality-dependent transverse momentum broadening transport coefficient q̂. To facilitate this undertaking, we develop a quantitative metric for validating the Bayesian workflow, which is used to analyze the sensitivity of various model parameters to individual observables. The usefulness of this new metric in improving Bayesian model emulation is shown to be highly beneficial for future such analyses. Published by the American Physical Society 2024

Reconstruction of unstable heavy particles using deep symmetry-preserving attention networks

Reconstructing unstable heavy particles requires sophisticated techniques to sift through the large number of possible permutations for assignment of detector objects to the underlying partons. An approach based on a generalized attention mechanism, symmetry preserving attention networks (SPA-NET), has been previously applied to top quark pair decays at the Large Hadron Collider which produce only hadronic jets. Here we extend the SPA-NET architecture to consider multiple input object types, such as leptons, as well as global event features, such as the missing transverse momentum. In addition, we provide regression and classification outputs to supplement the parton assignment. We explore the performance of the extended capability of SPA-NET in the context of semi-leptonic decays of top quark pairs as well as top quark pairs produced in association with a Higgs boson. We find significant improvements in the power of three representative studies: a search for tt¯H\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$t\\bar{t}H$$\\end{document}, a measurement of the top quark mass, and a search for a heavy Z′\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${Z}^{{\\prime} }$$\\end{document} decaying to top quark pairs. We present ablation studies to provide insight on what the network has learned in each case.

Status of dual-readout calorimetry for future high-energy physics experiments

Future experiments at high energy e + e - colliders will focus on extremely precise Standard Model measurements. Among the most important physics benchmarks, there is the capability to resolve the Higgs decays into W or Z pairs, in their completely hadronic decay modes (4 jets in the final state), only based on the invariant mass of the jet pair coming from decay of the on-shell boson. This translates into a relative energy resolution target of 30%/√E, well beyond current detector performances. Dual-readout calorimetry is a technique which aims to improve the energy resolution, for single hadrons and hadronic jets, exploiting the information produced by two different physical processes, namely scintillation and Čerenkov light emission. The IDEA detector, whose concept has been included in both the FCC and CEPC Conceptual Design Reports, is based on a dual-readout fibre calorimeter with independent fibre readout exploiting Silicon PhotoMultipliers (SiPMs). The individual SiPM information will be beneficial for a highly granular calorimeter design, opening up to advanced reconstruction techniques such as Particle Flow and a variety of neural network algorithms.In this paper the status of calorimeter prototypes that have been developed to demonstrate the feasibility of the dual-readout method in association with the high granularity feature is illustrated. The specific choice for the design of each prototype is presented, together with the performances achieved at high-energy test beams or through simulations.

Probing light quark Yukawa couplings through angularity distributions in Higgs boson decay

We propose to utilize angularity distributions in Higgs boson decay to probe light quark Yukawa couplings at e+e− colliders. Angularities τa are a class of 2-jet event shapes with variable and tunable sensitivity to the distribution of radiation in hadronic jets in the final state. Using soft-collinear effective theory (SCET), we present a prediction of angularity distributions from Higgs decaying to quark and gluon states at e+e− colliders to NNLL + \U0001d4aa(αs) accuracy. Due to the different color structures in quark and gluon jets, the angularity distributions from H → \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$q\\overline{q }$$\\end{document} and H → gg show different behaviors and can be used to constrain the light quark Yukawa couplings. We show that the upper limit of light quark Yukawa couplings could be probed to the level of ~ 15% of the bottom quark Yukawa coupling in the Standard Model in a conservative analysis window far away from nonperturbative effects and other uncertainties; the limit can be pushed to ≲ 7 – 9% with better control of the nonperturbative effects especially on gluon angularity distributions and/or with multiple angularities.

On heavy-flavour jets with Soft Drop

We study hadronic jets that are tagged as heavy-flavoured, i.e. they contain either beauty or charm. In particular, we consider heavy-flavour jets that have been groomed with the Soft Drop algorithm. In order to achieve a deeper understanding of these objects, we apply resummed perturbation theory to jets initiated by a massive quark and we perform analytic calculations for two variables that characterise Soft Drop jets, namely the opening angle and the momentum fraction of the splitting that passes Soft Drop. We compare our findings to Monte Carlo simulations. Furthermore, we investigate the correlation between the Soft Drop energy fraction and alternative observables that aim to probe heavy-quark fragmentation functions.

Exploring the spin structure of the nucleon at STAR

Understanding the internal spin structure of the nucleon remains a challenge in strong interaction physics. The unique capability of RHIC opened new avenues in studying the internal structure of the proton with unprecedented depth and precision. Significant progress has been made in the last few years through various measurements at STAR. The longitudinal spin measurements have contributed significantly to our understanding of the quark and gluon helicity distributions inside the proton. The longitudinal double-spin asymmetry, ALL, from STAR inclusive jet and dijet measurements provides the first evidence of a positive gluon polarization with partonic momentum fraction x > 0.05. The reconstruction of W±/Z in longitudinally polarized proton-proton collisions indicates that there is a flavor separation of the light sea quark helicity distributions. In transversely polarized proton collisions, W±/Z-bosons provide the first constraint on the sea-quark Sivers function and contributes to the tests of the predicted sign change. The tilt of the dijet opening angle provides a direct access to the first Mellin momentum of the Sivers function and avoids the spin-correlated fragmentation contributions. The novel measurements of the azimuthal distributions of identified hadrons in jets and spin-dependent dihadron correlations directly probe the collinear quark transversity in the proton, with the former coupled to the transverse momentum dependent (TMD) Collins fragmentation function and the latter to the dihadron interference fragmentation function. These measurements shed lights on Sivers function, quark transversity and spin-dependent fragmentation functions in both collinear and TMD formalism. In this proceeding, recent jet results on both the longitudinal and transverse spin structure of the proton from STAR are presented.

Deep Learning Approaches for LHCb ECAL Reconstruction

Calorimeters are a crucial component for most detectors mounted on modern colliders. Their tasks include identifying and measuring the energy of photons and neutral hadrons, recording energetic hadronic jets, and contributing to the identification of electrons, muons, and charged hadrons. To fulfill these many tasks while keeping costs reasonable, the calorimeter construction requires good and thoughtful balancing with other components of the detector. Much harder operation conditions during LHC’s high luminosity Run 5 and beyond bring new technological and computational challenges. This requires optimization of technologies, layouts, readouts, reconstruction algorithms to achieve the best overall physics performance for the limited cost. In the traditional approach, the reconstruction of the physical objects in the calorimeter must be matched to the calorimetric showers simulation used. We present a deep learning-based approach to help utilize raw simulated calorimetric data of varying degrees of detail.

Simulation of Measurements of the Fractions of Quark, Gluon, and Unidentified Jets in a Sample of Hadron Jets for the LHC

Simulation of Measurements of the Fractions of Quark, Gluon, and Unidentified Jets in a Sample of Hadron Jets for the LHC

Hadron productions and jet substructures associated with Z0/γ in Pb+Pb collisions at the LHC

Hadron productions and jet substructures associated with Z0/γ in Pb+Pb collisions at the LHC

Fast b-tagging at the high-level trigger of the ATLAS experiment in LHC Run 3

The ATLAS experiment relies on real-time hadronic jet reconstruction and b-tagging to record fully hadronic events containing b-jets. These algorithms require track reconstruction, which is computationally expensive and could overwhelm the high-level-trigger farm, even at the reduced event rate that passes the ATLAS first stage hardware-based trigger. In LHC Run 3, ATLAS has mitigated these computational demands by introducing a fast neural-network-based b-tagger, which acts as a low-precision filter using input from hadronic jets and tracks. It runs after a hardware trigger and before the remaining high-level-trigger reconstruction. This design relies on the negligible cost of neural-network inference as compared to track reconstruction, and the cost reduction from limiting tracking to specific regions of the detector. In the case of Standard Model HH → bb̅bb̅, a key signature relying on b-jet triggers, the filter lowers the input rate to the remaining high-level trigger by a factor of five at the small cost of reducing the overall signal efficiency by roughly 2%.

Tools for estimating fake/non-prompt lepton backgrounds with the ATLAS detector at the LHC

Measurements and searches performed with the ATLAS detector at the CERN LHC often involve signatures with one or more prompt leptons. Such analysesare subject to `fake/non-prompt' lepton backgrounds, where either a hadron or a lepton from a hadron decay or an electron from a photon conversion satisfies the prompt-leptonselection criteria. These backgrounds often arise within a hadronic jet because of particle decays in the showering process, particle misidentification or particleinteractions with the detector material. As it is challenging to model these processes with high accuracy in simulation, their estimation typically uses data-driven methods.Three methods for carrying out this estimation are described, along with their implementation in ATLAS and their performance.

LHC hadronic jet generation using convolutional variational autoencoders with normalizing flows

In high energy physics, one of the most important processes for collider data analysis is the comparison of collected and simulated data. Nowadays the state-of-the-art for data generation is in the form of Monte Carlo (MC) generators. However, because of the upcoming high-luminosity upgrade of the Large Hadron Collider (LHC), there will not be enough computational power or time to match the amount of needed simulated data using MC methods. An alternative approach under study is the usage of machine learning generative methods to fulfill that task. Since the most common final-state objects of high-energy proton collisions are hadronic jets, which are collections of particles collimated in a given region of space, this work aims to develop a convolutional variational autoencoder (ConVAE) for the generation of particle-based LHC hadronic jets. Given the ConVAE’s limitations, a normalizing flow (NF) network is coupled to it in a two-step training process, which shows improvements on the results for the generated jets. The ConVAE+NF network is capable of generating a jet in , making it one of the fastest methods for this task up to now.

Search for supersymmetry in final states with a single electron or muon using angular correlations and heavy-object identification in proton-proton collisions at s\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\sqrt{s} $$\\end{document} = 13 TeV

A search for supersymmetry is presented in events with a single charged lepton, electron or muon, and multiple hadronic jets. The data correspond to an integrated luminosity of 138 fb−1 of proton-proton collisions at a center-of-mass energy of 13 TeV, recorded by the CMS experiment at the CERN LHC. The search targets gluino pair production, where the gluinos decay into final states with the lightest supersymmetric particle (LSP) and either a top quark-antiquark (tt¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \ extrm{t}\\overline{\ extrm{t}} $$\\end{document}) pair, or a light-flavor quark-antiquark (qq¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \ extrm{q}\\overline{\ extrm{q}} $$\\end{document}) pair and a virtual or on-shell W boson. The main backgrounds, tt¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \ extrm{t}\\overline{\ extrm{t}} $$\\end{document} pair and W+jets production, are suppressed by requirements on the azimuthal angle between the momenta of the lepton and of its reconstructed parent W boson candidate, and by top quark and W boson identification based on a machine-learning technique. The number of observed events is consistent with the expectations from standard model processes. Limits are evaluated on supersymmetric particle masses in the context of two simplified models of gluino pair production. Exclusions for gluino masses reach up to 2120 (2050) GeV at 95% confidence level for a model with gluino decay to a tt¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \ extrm{t}\\overline{\ extrm{t}} $$\\end{document} pair (a qq¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \ extrm{q}\\overline{\ extrm{q}} $$\\end{document} pair and a W boson) and the LSP. For the same models, limits on the mass of the LSP reach up to 1250 (1070) GeV.

Search for Majorana neutrinos in same-sign WW scattering events from pp collisions at sqrt{s}=13 TeV

A search for Majorana neutrinos in same-sign WW scattering events is presented. The analysis uses sqrt{s}= 13 TeV proton–proton collision data with an integrated luminosity of 140 fb^{-1} recorded during 2015–2018 by the ATLAS detector at the Large Hadron Collider. The analysis targets final states including exactly two same-sign muons and at least two hadronic jets well separated in rapidity. The modelling of the main backgrounds, from Standard Model same-sign WW scattering and WZ production, is constrained with data in dedicated signal-depleted control regions. The distribution of the transverse momentum of the second-hardest muon is used to search for signals originating from a heavy Majorana neutrino with a mass between 50 GeV and 20 TeV. No significant excess is observed over the background expectation. The results are interpreted in a benchmark scenario of the Phenomenological Type-I Seesaw model. In addition, the sensitivity to the Weinberg operator is investigated. Upper limits at the 95% confidence level are placed on the squared muon-neutrino–heavy-neutrino mass-mixing matrix element vert V_{mu N} vert ^{2} as a function of the heavy Majorana neutrino’s mass m_N, and on the effective mu mu Majorana neutrino mass |m_{mu mu }|.

Measurements of W^{+}W^{-} production in decay topologies inspired by searches for electroweak supersymmetry

This paper presents a measurement of fiducial and differential cross-sections for W^{+}W^{-} production in proton–proton collisions at sqrt{s}=13 TeV with the ATLAS experiment at the Large Hadron Collider using a dataset corresponding to an integrated luminosity of 139 fb^{-1}. Events with exactly one electron, one muon and no hadronic jets are studied. The fiducial region in which the measurements are performed is inspired by searches for the electroweak production of supersymmetric charginos decaying to two-lepton final states. The selected events have moderate values of missing transverse momentum and the ‘stransverse mass’ variable m_{textrm{T2}}, which is widely used in searches for supersymmetry at the LHC. The ranges of these variables are chosen so that the acceptance is enhanced for direct W^{+}W^{-} production and suppressed for production via top quarks, which is treated as a background. The fiducial cross-section and particle-level differential cross-sections for six variables are measured and compared with two theoretical SM predictions from perturbative QCD calculations.