Gluon Jets Research Articles

Separation of quark and gluon jets in heavy ion collisions at high energies

The possibility of separating quark and gluon jets in heavy ion collisions, both in the presence of the jet quenching effect and in its absence, has been investigated. Using machine learning methods, a technique has been developed to recover the fraction of quark and gluon jets, using variables characterizing the shape, multiplicity, and charge of the jet. The potential of using these variables to study the characteristics of the dense medium that arises during high-energy ion collisions has been demonstrated.

Determining the CP property of [formula omitted] coupling via a novel jet substructure observable

Determining the CP property of the Higgs boson is important for a precision test of the Standard Model as well as for the search for new physics. We propose a novel jet substructure observable based on the azimuthal anisotropy in a linearly polarized gluon jet that is produced in association with a Higgs boson at hadron colliders, and demonstrate that it provides a new CP-odd observable for determining the CP property of the Higgs-top interaction. We introduce a factorization formalism to define a polarized gluon jet function with the insertion of an infrared-safe azimuthal observable to capture the linear polarization.

Model Uncertainty in Measuring the Gluon Jet Fraction at the Hadron Collider

Model Uncertainty in Measuring the Gluon Jet Fraction at the Hadron Collider

Infrared-safe energy weighting does not guarantee small nonperturbative effects

Infrared and collinear (IRC) safety has long been used a proxy for robustness when developing new jet substructure observables. This guiding philosophy has been carried into the deep learning era, where IRC-safe neural networks have been used for many jet studies. For graph-based neural networks, the most straightforward way to achieve IRC safety is to weight particle inputs by their energies. However, energy-weighting by itself does not guarantee that perturbative calculations of machine-learned observables will enjoy small nonperturbative corrections. In this paper, we demonstrate the sensitivity of IRC-safe networks to nonperturbative effects, by training an energy flow network (EFN) to maximize its sensitivity to hadronization. We then show how to construct Lipschitz energy flow networks (L-EFNs), which are both IRC safe and relatively insensitive to nonperturbative corrections. We demonstrate the performance of L-EFNs on generated samples of quark and gluon jets, and showcase fascinating differences between the learned latent representations of EFNs and L-EFNs. Published by the American Physical Society 2024

Three-point energy correlators in hadronic Higgs boson decays

We present the analytic calculation of the leading-order three-point energy correlator (EEEC) in hadronic Higgs decays, including both the gluon-initiated channel H→gg+X and quark-initiated channel H→qq¯+X. The phase-space integration is evaluated directly using Mandelstam variables sij=(pi+pj)2, and the appearing square roots can be rationalized by either conformal ratios or celestial coordinate variables. Throughout the calculation, we observe the same transcendental function space as in N=4 super–Yang-Mills theory and e+e−→hadrons. Different infrared limits are also explored using the full analytic result, offering the fixed-order data for EEEC factorization and resummation. Given its nontrivial shape dependence, the EEEC presents an excellent opportunity to explore the dynamics of gluon jets originating from the H→gg decay channel at future lepton colliders. Published by the American Physical Society 2024

Collinear fragmentation at NNLL: generating functionals, groomed correlators and angularities

Jet calculus offers a unique mathematical technique to bridge the area of QCD resummation with Monte Carlo parton showers. With the ultimate goal of constructing next-to-next-to-leading logarithmic (NNLL) parton showers we study, using the language of generating functionals, the collinear fragmentation of final-state partons. In particular, we focus on the definition and calculation of the Sudakov form factor, which physically describes the no-emission probability in an ordered branching process. We review recent results for quark jets and compute the Sudakov form factor for the collinear fragmentation of gluon jets at NNLL. The NNLL corrections are encoded in a z dependent two-loop anomalous dimension B\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\mathcal{B} $$\\end{document}2(z), with z being a suitably defined longitudinal momentum fraction. This is obtained from the integration of the relevant 1 → 3 collinear splitting kernels combined with the one-loop corrections to the 1 → 2 counterpart. This work provides the missing ingredients to extend the methods of jet calculus in the collinear limit to NNLL and gives an important element of the next generation of NNLL parton shower algorithms. As an application we derive new NNLL results for both the fractional moments of energy-energy correlation FCx and the angularities λx measured on mMDT/Soft-Drop (β = 0) groomed jets.

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.

Measuring the Fractions of Quark and Gluon Jets in Hardon–Hadron Collisions

Measuring the Fractions of Quark and Gluon Jets in Hardon–Hadron Collisions

Novel approach to measure quark/gluon jets at the LHC

In this paper, we present a new proposal on how to measure quark/gluon jet properties at the LHC. The measurement strategy takes advantage of the fact that the LHC has collected data at different energies. Measurements at two or more energies can be combined to yield distributions of any jet property separated into quark and gluon jet samples on a statistical basis, without the need for an independent event-by-event tag. We illustrate our method with a variety of different angularity observables, and discuss how to narrow down the search for the most useful observables.

New Approach to Measuring Quark–Gluon Jets at the LHC

New Approach to Measuring Quark–Gluon Jets at the LHC

New Idea to Probe Properties of Quark–Gluon Jets at the LHC

New Idea to Probe Properties of Quark–Gluon Jets at the LHC

Baryon correlations in Pythia

We present the results from our investigation of angular correlations between baryons pairs in the Pythia8 event generator. We show how colour reconnection models and hadronization mechanisms influence such angular correlations and in particular address the effect of gluons on the baryon production mechanism in the Lund string fragmentation model. We conclude by discussing the new theoretical ideas in comparison with the ALICE pp\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ extrm{pp} $$\\end{document} collision results for the baryon angular correlations. We propose a hypothesis for suppressing baryons produced in gluon jets and show how that may influence the angular correlations.

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

Identifying D Mesons from Radiative W Decays at the Large Hadron Collider

In this paper, we present two machine learning algorithms to identify D mesons produced in a colour singlet state from radiative W boson decays at the LHC. The combined network algorithm is able to identify D mesons via its hadronic decays with an efficiency of 47% while suppressing a background of quark and gluon jets by a factor of 100. Using the developed algorithm, we perform a prospective study for the measurement of B(W→Dsγ).

Separation of Quark and Gluon Jets in Heavy Ion Collisions at High Energies

Separation of Quark and Gluon Jets in Heavy Ion Collisions at High Energies

Unraveling gluon jet quenching through [formula omitted] production in heavy-ion collisions

Jet quenching has long been regarded as one of the key signatures for the formation of quark-gluon plasma in heavy-ion collisions. Despite significant efforts, the separate identification of quark and gluon jet quenching has remained as a challenge. Here we show that J/ψ in high transverse momentum (pT) region provides a uniquely sensitive probe of in-medium gluon energy loss since its production at high pT is particularly dominated by gluon fragmentation. Such gluon-dominance is first demonstrated for the baseline of proton-proton collisions within the framework of leading power non-relativistic quantum chromodynamics factorization formalism. We then use the linear Boltzmann transport model combined with hydrodynamics for the simulation of jet-medium interaction in nucleus-nucleus collisions. The satisfactory description of experimental data on both nuclear modification factor RAA and elliptic flow v2 reveals, for the first time, that the gluon jet quenching is the driving force for high pTJ/ψ suppression. This novel finding is further confirmed by the data-driven Bayesian analyses of relevant experimental measurements, from which we also obtain the first quantitative extraction of the gluon energy loss distribution in the quark-gluon plasma.

Disentangling quark and gluon jets with normalizing flows

The isolation of pure samples of quark and gluon jets is of key interest at hadron colliders. Recent work has employed topic modeling to disentangle the underlying distributions in mixed samples obtained from experiments. However, current implementations do not scale to high-dimensional observables as they rely on binning the data. In this work we introduce TopicFlow, a method based on normalizing flows to learn quark and gluon jet topic distributions from mixed datasets. These networks are as performant as the histogram-based approach, but since they are unbinned, they are efficient even in high dimension. The models can also be oversampled to alleviate the statistical limitations of histograms. As an example use case, we demonstrate how our models can improve the calibration accuracy of a classifier. Finally, we discuss how the flow likelihoods can be used to perform outlier-robust quark/gluon classification.

Gluon jets evolution in the quest for new physics

In this paper, our task is to review the evolution of Gluon Jets in view of the quest for physics beyond the Standard Model (SM) – the so called New Physics (NP). One of the major goals of the Large Hadron Collider (LHC) is to understand a new mode of matter called the Quark Gluon Plasma (QGP). This seemingly new form of matter consists of a confinement of quarks and gluons observed at very high temperature and density. This paper focuses on heavy ion collisions in order to get an understanding of the interaction of high momentum partons. It is these highly sophisticated interactions that probe quantum chromodynamics theorem at very high temperatures and densities. This results in the QGP phase of NP via propagation of very energetic Gluon Jets.

Prospects for strong coupling measurement at hadron colliders using soft-drop jet mass

We compute the soft-drop jet-mass distribution from pp collisions to NNLL accuracy while including nonperturbative corrections through a field-theory based formalism. Using these calculations, we assess the theoretical uncertainties on an αs precision measurement due to higher order perturbative effects, nonperturbative corrections, and PDF uncertainty. We identify which soft-drop parameters are well-suited for measuring αs, and find that higher-logarithmic resummation has a qualitatively important effect on the shape of the jet-mass distribution. We find that quark jets and gluon jets have similar sensitivity to αs, and emphasize that experimentally distinguishing quark and gluon jets is not required for an αs measurement. We conclude that measuring αs to the 10% level is feasible now, and with improvements in theory a 5% level measurement is possible. Getting down to the 1% level to be competitive with other state-of-the-art measurements will be challenging.

Experimental verification of two types of gluon jets in QCD

The Abelian decomposition of QCD tells that there are two types of gluons, the color neutral neurons and colored chromons. We propose to confirm the Abelian decomposition testing the existence of two types of gluon jets experimentally. We predict that one quarter of the gluon jet is made of the neurons which has the color factor $3/4$ and the sharpest jet radius and smallest charged particle multiplicity, while the three quarters of the gluon jet are made of the chromons with the color factor $9/4$, which have the broadest jet radius (broader than the quark jet). Moreover, we argue that the neuron jet has a distinct color flow which forms an ideal color dipole, while the quark and chromon jets have distorted dipole pattern. To test the plausibility of this proposal, we suggest to analyze the gluon distribution against the jet shape (the sphericity) and/or particle multiplicity from the existing gluon jet events and look for two distinct peaks in the distribution.