Event Topology Research Articles

Secondary lepton production, propagation, and interactions

Charged current interactions of neutrinos inside the Earth can result in secondary muons and τ-leptons which are detectable by several existing and planned neutrino experiments through a wide variety of event topologies. Consideration of such events can improve detector performance and provide unique signatures which help with event reconstruction. In this work, we describe , a propagation tool for neutrinos and charged leptons that builds on the fast framework. considers energy losses of charged leptons, modeled both continuously for performance or stochastically for accuracy, as well as interaction models for all flavors of neutrinos, including the Glashow resonance. We demonstrate the results from including these effects on the Earth emergence probability of various charged leptons from different flavors of primary neutrino and their corresponding energy distributions. We find that the emergence probability of muons can be higher than that of taus for energies below 100 PeV, whether from a primary muon or τ neutrino, and that the Glashow resonance contributes to a surplus of emerging leptons near the resonant energy. Published by the American Physical Society 2025

Exploring Ultraperipheral Heavy Ion Collisions in CMS Run III

Ultraperipheral collisions (UPCs) of heavy ions are a useful probe to study nuclear parton distribution functions (nPDFs) and, in particular, to characterize nuclear matter at Bjorken x < 10−3 and low squared momentum transfer Q2 (shadowing/saturation regime). In order to fully exploit these collisions, dedicated triggers on such event topologies were developed for the heavy ion data-taking period in 2023 by the CMS experiment. These triggers relied on the possibility of using the Zero Degree Calorimeter (ZDC) as a level-1 (L1) trigger detector for the first time. As a result, they allowed for an improved selection performance in addition to existing UPC triggers (as well as minimum-bias hadronic triggers), and enabled the study of hard processes (jets and heavy flavor hadrons) in photon-photon (γγ) and photon-nucleus (γN) scatterings [1].

Estimation of the Chances to Find New Phenomena at the LHC in a Model-Agnostic Combinatorial Analysis

In this paper, we estimate the number of event topologies that have the potential to be produced in pp collisions at the Large Hadron Collider (LHC) without violating kinematic and other constraints. We use numerical calculations and combinatorics, guided by large-scale Monte Carlo simulations of Standard Model (SM) processes. Then, we set the upper limit on the probability that new physics may escape detection, assuming a model-agnostic approach. The calculated probability is unexpectedly large, and the fact that LHC has not found new physics until now is not entirely surprising. Theoretical limitations and experimental challenges in observing new physics within the studied exclusive event classes are examined.

Measurement of groomed event shape observables in deep-inelastic electron-proton scattering at HERA

The H1 Collaboration at HERA reports the first measurement of groomed event shape observables in deep inelastic electron-proton scattering (DIS) at s=319\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sqrt{s} =319~$$\\end{document}GeV, using data recorded between the years 2003 and 2007 with an integrated luminosity of 351 pb-1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ extrm{pb}^{-1}$$\\end{document}. Event shapes provide incisive probes of perturbative and non-perturbative QCD. Grooming techniques have been used for jet measurements in hadronic collisions; this paper presents the first application of grooming to DIS data. The analysis is carried out in the Breit frame, utilizing the novel Centauro jet clustering algorithm that is designed for DIS event topologies. Events are required to have squared momentum-transfer Q2>150\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$Q^2 > 150$$\\end{document} GeV2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^2$$\\end{document} and inelasticity 0.2<y<0.7\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ 0.2< y < 0.7$$\\end{document}. We report measurements of the production cross section of groomed event 1-jettiness and groomed invariant mass for several choices of grooming parameter. Monte Carlo model calculations and analytic calculations based on Soft Collinear Effective Theory are compared to the measurements.

Neutrino oscillations with atmospheric neutrinos at large liquid argon TPCs

Neutrino oscillations with atmospheric neutrinos at large liquid argon TPCs

Doubly heavy hadron production in ultraperipheral collision

We study the double heavy baryon ΞQQ′ and tetraquark TQQ production through photon-photon and photon-gluon fusion via ultraperipheral collisions at the LHC and Future Circular Collider (FCC) within the framework of nonrelativistic QCD factorization formalism. Various ion-ion collisions are taken into account, two cc(bb)-diquark configurations ([cc(bb),S31−3¯] and [cc(bb),S10−6]) and four bc-diquark configurations ([bc,S31−3¯], [bc,S31−6], [bc,S10−3¯], and [bc,S10−6]) are considered in the calculation. Numerical results indicate that the [cc,S31−3¯] diquark provides dominant contribution for Ξcc (Tcc) production, and a considerable number of Ξcc (Tcc) can be produced. Because the event topologies for ultraperipheral collision are very clear, the background from various QCD interactions can be suppressed, hence the experimental investigation for Ξcc and Tcc is feasible. The productions for Ξbc/bb are also discussed, leaving only a slight possibility for Ξbc through photon-gluon fusion with ultraperipheral collisions at the FCC. Published by the American Physical Society 2024

Topological heavy-flavor tagging and intrinsic bottom at the Electron-Ion Collider

Heavy-flavor hadron production, in particular bottom hadron production, is difficult to study in deep-inelastic scattering (DIS) experiments due to small production rates and branching fractions. To overcome these limitations, a method for identifying heavy-flavor DIS events based on event topology is proposed. Based on a heavy-flavor jet tagging strategy developed for the LHCb experiment, this algorithm uses displaced vertices to identify decays of heavy-flavor hadrons. The algorithm’s performance at the Electron-Ion Collider is demonstrated using simulation, and it is shown to provide discovery potential for nonperturbative intrinsic bottom quarks in the proton. Published by the American Physical Society 2024

Real-time charged track reconstruction for CLAS12

This paper presents the results of charged particle track reconstruction in CLAS12 using artificial intelligence. In our approach, we use machine learning algorithms to reconstruct tracks, including their momentum and direction, with high accuracy from raw hits of the CLAS12 drift chambers. The reconstruction is performed in real-time, with the rate of data acquisition, and allows for the identification of event topologies in real-time. This approach revolutionizes the Nuclear Physics experiments' data processing, allowing us to identify and categorize the experimental data on the fly, and will lead to a significant reduction in experiment data processing. It can also be used in streaming readout applications leading to more efficient data acquisition and post-processing.

Λ(1520) resonance production with respect to transverse spherocity using EPOS3+UrQMD

Resonances are sensitive to the properties of the medium created in heavy ion collision. They also provide insight into the properties of the hadronic phase. Studying the dependence of the yield of resonances on transverse spherocity and multiplicity allows us to understand the resonance production mechanism with event topology and system size, respectively. The results reported pertain to \Lambda(1520)Λ(1520), using predictions from EPOS3+UrQMD event generator.

New measurements of inclusive jet suppression and jet ν2 in Pb–Pb collisions at √SNN = 5.02 TeV with ALICE

We report measurements of the inclusive charged-particle jet yield in central Pb–Pb collisions at √SNN = 5.02 TeV. Uncorrelated background is suppressed by a novel mixed-event technique, enabling extension of the jet RAA measurement down to pT = 13.5 GeV/c, with kinematic overlap with RHIC jet measurements. We also present measurements of inclusive charged-particle jet v2 in semi-central Pb–Pb collisions at √SNN = 5.02 TeV, and azimuthal dependence of jet yield suppression for event topologies selected using eventshape engineering.

Search for non-resonant production of semi-visible jets using Run 2 data in ATLAS

Search for non-resonant production of semi-visible jets using Run 2 data in ATLAS

NEXT-CRAB-0: a high pressure gaseous xenon time projection chamber with a direct VUV camera based readout

The search for neutrinoless double beta decay (0νββ) remains one of the most compelling experimental avenues for the discovery in the neutrino sector. Electroluminescent gas-phase time projection chambers are well suited to 0νββ searches due to their intrinsically precise energy resolution and topological event identification capabilities. Scalability to ton- and multi-ton masses requires readout of large-area electroluminescent regions with fine spatial resolution, low radiogenic backgrounds, and a scalable data acquisition system. This paper presents a detector prototype that records event topology in an electroluminescent xenon gas TPC via VUV image-intensified cameras. This enables an extendable readout of large tracking planes with commercial devices that reside almost entirely outside of the active medium. Following further development in intermediate scale demonstrators, this technique may represent a novel and enlargeable method for topological event imaging in 0νββ.

Uncovering tau leptons-enriched semi-visible jets at the LHC

This Letter proposes a new signature for confining dark sectors at the Large Hadron Collider. Under the assumption of a QCD-like hidden sector, hadronic jets containing stable dark bound states could manifest in proton-proton collisions. We present a simplified model with a Z' boson yielding the production of jets made up of dark bound states and subsequently leading to the decays of those that are unstable to tau leptons and Standard Model quarks. The resulting signature is characterised by non-isolated tau lepton pairs inside semi-visible jets. We estimate the constraints on our model from existing CMS and ATLAS analyses. We propose a set of variables that leverage the leptonic content of the jet and exploit them in a supervised jet tagger to enhance the signal-to-background separation. Furthermore, we discuss the performance and limitations of current triggers for accessing sub-TeV Z' masses, as well as possible strategies that can be adopted by experiments to access such low mass regions. We estimate that with the currently available triggers, a high mass search can claim a 5 sigma discovery (exclusion) of the Z' boson with a mass up to 4.5 TeV (5.5 TeV) with the full Run 2 data of the LHC when the fraction of unstable dark hadrons decaying to tau lepton pairs is around 50%, and with a coupling of the Z' to right-handed up-type quarks of 0.25. Furthermore, we show that, with new trigger strategies for Run 3, it may be possible to access Z' masses down to 700 GeV, for which the event topology is still composed of two resolved semi-visible jets.

3D track reconstruction of low-energy electrons in the MIGDAL low pressure optical time projection chamber

We demonstrate three-dimensional track reconstruction of electrons in a low pressure (50 Torr) optical TPC consisting of two glass GEMs with an ITO strip readout in CF4 and CF4/Ar mixtures. The reconstructed tracks show a variety of event topologies, including short tracks from photoelectrons induced by 55Fe 5.9 keV X-rays and long tracks from gamma ray interactions and beta decays. Algorithms for event identification and track ridge detection are discussed as well as multiple methods for integrating information from the camera image and ITO waveforms with the goal of full 3D reconstruction of the track.

Study of charged particle production at high pT using event topology in pp, p–Pb and Pb–Pb collisions at [formula omitted] TeV

This letter reports measurements which characterize the underlying event associated with hard scatterings at mid-pseudorapidity (|η|<0.8) in pp, p–Pb and Pb–Pb collisions at centre-of-mass energy per nucleon pair, sNN=5.02 TeV. The measurements are performed with ALICE at the LHC. Different multiplicity classes are defined based on the event activity measured at forward rapidities. The hard scatterings are identified by the leading particle defined as the charged particle with the largest transverse momentum (pT) in the collision and having 8 <pT<15 GeV/c. The pT spectra of associated particles (0.5 ≤pT<6 GeV/c) are measured in different azimuthal regions defined with respect to the leading particle direction: toward, transverse, and away. The associated charged particle yields in the transverse region are subtracted from those of the away and toward regions. The remaining jet-like yields are reported as a function of the multiplicity measured in the transverse region. The measurements show a suppression of the jet-like yield in the away region and an enhancement of high-pT associated particles in the toward region in central Pb–Pb collisions, as compared to minimum-bias pp collisions. These observations are consistent with previous measurements that used two-particle correlations, and with an interpretation in terms of parton energy loss in a high-density quark gluon plasma. These yield modifications vanish in peripheral Pb–Pb collisions and are not observed in either high-multiplicity pp or p–Pb collisions.

Cross-section measurements for the production of a Z boson in association with high-transverse-momentum jets in pp collisions at sqrt{s} = 13 TeV with the ATLAS detector

Cross-section measurements for a Z boson produced in association with high-transverse-momentum jets (pT ≥ 100 GeV) and decaying into a charged-lepton pair (e+e−, μ+μ−) are presented. The measurements are performed using proton–proton collisions at sqrt{s} = 13 TeV corresponding to an integrated luminosity of 139 fb−1 collected by the ATLAS experiment at the LHC. Measurements of angular correlations between the Z boson and the closest jet are performed in events with at least one jet with pT ≥ 500 GeV. Event topologies of particular interest are the collinear emission of a Z boson in dijet events and a boosted Z boson recoiling against a jet. Fiducial cross sections are compared with state-of-the-art theoretical predictions. The data are found to agree with next-to-next-to-leading-order predictions by NNLOjet and with the next-to-leading-order multi-leg generators MadGraph5_aMC@NLO and Sherpa.

Search for Higgs boson decays to a Z boson and a photon in proton-proton collisions at sqrt{s} = 13 TeV

Results are presented from a search for the Higgs boson decay H → Zγ, where Z → ℓ+ℓ− with ℓ = e or μ. The search is performed using a sample of proton-proton (pp) collision data at a center-of-mass energy of 13 TeV, recorded by the CMS experiment at the LHC, corresponding to an integrated luminosity of 138 fb−1. Events are assigned to mutually exclusive categories, which exploit differences in both event topology and kinematics of distinct Higgs production mechanisms to enhance signal sensitivity. The signal strength μ, defined as the product of the cross section and the branching fraction left[sigma left(textrm{pp}to textrm{H}right)mathcal{B}left(textrm{H}to textrm{Z}upgamma right)right] relative to the standard model prediction, is extracted from a simultaneous fit to the ℓ+ℓ−γ invariant mass distributions in all categories and is measured to be μ = 2.4 ± 0.9 for a Higgs boson mass of 125.38 GeV. The statistical significance of the observed excess of events is 2.7 standard deviations. This measurement corresponds to left[sigma left(textrm{pp}to textrm{H}right)mathcal{B}left(textrm{H}to textrm{Z}upgamma right)right]=0.21pm 0.08 pb. The observed (expected) upper limit at 95% confidence level on μ is 4.1 (1.8), where the expected limit is calculated under the background-only hypothesis. The ratio of branching fractions mathcal{B}left(textrm{H}to textrm{Z}upgamma right)/mathcal{B}left(textrm{H}to upgamma upgamma right) is measured to be {1.5}_{-0.6}^{+0.7} , which agrees with the standard model prediction of 0.69 ± 0.04 at the 1.5 standard deviation level.

The Fake Factor Method and its relation to the Matrix Method

The two main analysis methods used in high-energy physics to estimate difficult backgrounds with misidentified leptons are the Fake Factor Method and Matrix Method. They are often mentioned peripherally without rigorous derivation. This paper serves two purposes: First, it reviews the motivation and requirements of the methods and shows how single-lepton estimates are performed. Second, it illustrates the connection between the two methods with a proof that the Fake Factor Method can be derived exactly from the Matrix Method. For the first time, a generalized derivation is provided for event topologies with an arbitrary number of leptons.

The MIGDAL experiment: Measuring a rare atomic process to aid the search for dark matter

The MIGDAL experiment: Measuring a rare atomic process to aid the search for dark matter

Probing initial geometrical anisotropy and final azimuthal anisotropy in heavy-ion collisions at Large Hadron Collider energies through event-shape engineering

Anisotropic flow is accredited to have effects from the initial state geometry and fluctuations in the nuclear overlap region. The elliptic flow (${v}_{2}$) and triangular flow (${v}_{3}$) coefficients of the final state particles are expected to have influenced by eccentricity (${ϵ}_{2}$) and triangularity (${ϵ}_{3}$) of the participants, respectively. In this work, we study ${v}_{2}$, ${v}_{3}$, ${ϵ}_{2}$, ${ϵ}_{3}$, and the correlations among them with respect to event topology in the framework of a multiphase transport model (AMPT). We use transverse spherocity and reduced flow vector as event shape classifiers in this study. Transverse spherocity has the unique ability to separate events based on geometrical shapes, i.e., jetty and isotropic, which pertain to pQCD and non-pQCD domains of particle production in high-energy physics, respectively. We use the two-particle correlation method to study different anisotropic flow coefficients. We confront transverse spherocity with a more widely used event shape classifier--reduced flow vector (${q}_{n}$) and they are found to have significant (anti)correlations among them. We observe significant spherocity dependence on ${v}_{2}$, ${v}_{3}$, and ${ϵ}_{2}$. This work also addresses transverse momentum dependent crossing points between ${v}_{2}$ and ${v}_{3}$, which varies for different centrality and spherocity percentiles.