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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Classical gluon fields of relativistic color charges

The objective of the present study is to consider in more detail the exotic color-charge-glow effect discovered recently and to analyze its possible physical manifestations associated with the treatment of ensembles of color-charged particles at a classical level. The ways in which this effect may appear in arbitrary systems consisting of pointlike massive particles and admitting the partition into elementary configurations like color charges and color dipoles are studied. The possible influence of this effect on particle dynamics (in particular, on gluon distributions) is also examined. Particle collisions at a given impact parameters are considered for a natural regularization of emerging expressions. It is shown that, in the case of reasonable impact-parameter values, collisions may proceed in the electrodynamic mode, in which case the charge-glow contribution to field strengths is suppressed in relation to what we have in the electrodynamic picture. From an analysis of the color-echo situation, it follows that the above conclusion remains valid for more complicated particle configurations as well, since hard gluon fields may arise only owing to a direct collision rather than owing to any echo-like effects.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2013

Saturation of gluon density and soft pp collisions at LHC

We find the relation of the unintegrated gluon distribution at low intrinsic transverse momenta to the inclusive spectrum of the hadrons produced in pp collision at LHC energies in the mid-rapidity region and low hadron transverse momenta. It allows us to study the saturation of the gluon density at low Q{sup 2} more carefully and find the saturation scale that does not contradict to both the LHC and HERA data.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2014

Can gluon spin contribute to that of nucleon?

The transformation of angular momentum to its Belinfante form requires the smooth behaviour of classical fields at infinity which for the case of quantum operators transforms to the smooth behaviour of matrix elements at small momentum transfers. For the case of quarks this provides the kinematical counterpart of U {sub A }(1) problem while for gluons there is a contradiction between kinematics and dynamics governed by Kogut-Susskind pole. This may result in the violation of Equivalence Principle for nucleons or in the stringent constraints to the strange quark polarization in nucleons, while the most likely outcome would be the impossibility to separate gluon angular momentum to spin and orbital parts in the meaningful way.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

SUSY-Like Relation in Evolution of Gluon and Quark Jet Multiplicities

We show the new relationship [1] between the anomalous dimensions, resummed through next-to-next-to-leading-logarithmic order, in the Dokshitzer–Gribov–Lipatov–Altarelli–Parisi (DGLAP) evolution equations for the first Mellin moments D{sub q,g}(μ{sup 2}) of the quark and gluon fragmentation functions, which correspond to the average hadron multiplicities in jets initiated by quarks and gluons, respectively. This relationship, which is independent of the number of quark flavors, strongly improves previous treatments by allowing for an exact solution of the evolution equations. So far, such relationships have only been known from supersymmetric QCD.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

Probing Nuclear Gluons with Heavy Flavor Production at EIC

The nuclear modifications of the parton densities in different regions of x (EMC effect, antishadowing, shadowing) reveal aspects of the fundamental QCD substructure of nucleon interactions in the nucleus. Here, we study the feasibility of measuring nuclear gluon densities at large x using open heavy flavor production (charm, beauty) in DIS at EIC. This in- cludes (a) charm production rates and kinematic dependences; (b) charm reconstruction at large x B using exclusive and inclusive modes, enabled by particle identification and vertex detection; (c) impact of inclusive charm data on nuclear gluon density.

EMC effect↗
DOE OSTI2012

The physics of hot and dense quark-gluon matter

This technical report describes the work done under the DOE grant DE-FG-88ER41723 (final award number DE-SC0005645), "The physics of hot and dense quark-gluon matter", during the year of 12/01/2010 through 11/30/2011. As planned in the proposal, the performed research focused along two main thrusts: 1) topological effects in hot quark-gluon matter and 2) phenomenology of relativistic heavy ion collisions. The results of research are presented in 12 papers published in reputable refereed journals (Physical Review Letters, Physical Review, Physics Letters and Nuclear Physics). All of the performed research is directly related to the experimental programs of DOE, especially at the Relativistic Heavy Ion Collider. Much of it also has broader interdisciplinary implications - for example, the work on the non-dissipative chiral magnetic current is directly relevant for quantum computing. The attached report describes the performed work in detail.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Accessing the Distribution of Linearly Polarized Gluons in Unpolarized Hadrons

Gluons inside unpolarized hadrons can be linearly polarized provided they have a nonzero transverse momentum. The simplest and theoretically safest way to probe this distribution of linearly polarized gluons is through cos2{phi} asymmetries in heavy quark pair or dijet production in electron-hadron collisions. Future Electron-Ion Collider (EIC) or Large Hadron electron Collider (LHeC) experiments are ideally suited for this purpose. Here we estimate the maximum asymmetries for EIC kinematics.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Probing the Linear Polarization of Gluons in Unpolarized Hadrons at EIC

Gluons inside unpolarized hadrons can be linearly polarized provided they have a nonzero transverse momentum. The simplest and theoretically safest way to probe this TMD distribution of linearly polarized gluons is through cos 2{phi} asymmetries in heavy quark pair or dijet production in electron-hadron collisions. Future EIC or LHeC experiments are ideally suited for this purpose. Here we estimate the maximum asymmetries for EIC kinematics.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2012

Searching for $Z'$ bosons decaying to gluons

The production and decay of a new heavy vector boson, a chromophilic Z{prime} vector boson, is described. The chromophilic Z{prime} couples only to two gluons, but its two-body decays are absent, leading to a dominant decay mode of Z{prime} {yields} q{bar q}g. The unusual nature of the interaction predicts a cross-section which grows with m{sub Z{prime}} for a fixed coupling and an accompanying gluon with a coupling that rises with its energy. We study the t{bar t}g decay mode, proposing distinct reconstruction techniques for the observation of an excess and for the measurement of m{sub Z{prime}}. We estimate the sensitivity of current experimental datasets.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Next-to-Eikonal Corrections to Soft Gluon Radiation: A Diagrammatic Approach

We consider the problem of soft gluon resummation for gauge theory amplitudes and cross sections, at next-to-eikonal order, using a Feynman diagram approach. At the amplitude level, we prove exponentiation for the set of factorizable contributions, and construct effective Feynman rules which can be used to compute next-to-eikonal emissions directly in the logarithm of the amplitude, finding agreement with earlier results obtained using path-integral methods. For cross sections, we also consider sub-eikonal corrections to the phase space for multiple soft-gluon emissions, which contribute to next-to-eikonal logarithms. To clarify the discussion, we examine a class of log(1 - x) terms in the Drell-Yan cross-section up to two loops. Our results are the first steps towards a systematic generalization of threshold resummations to next-to-leading power in the threshold expansion.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Phenomenological analysis of Higgs boson production through gluon fusion in association with jets

We present a detailed phenomenological analysis of the production of a Standard Model Higgs boson in association with up to three jets. We consider the gluon fusion channel using an effective theory in the large top-quark mass limit. Higgs boson production in gluon fusion constitutes an irreducible background to the vector boson fusion (VBF) process; hence the precise knowledge of its characteristics is a prerequisite for any measurement in the VBF channel. The calculation is carried out at next-to-leading order (NLO) in QCD in a fully automated way by combining the two programs GoS AM and SHERPA. We present numerical results for a large variety of observables for both standard cuts and VBF selection cuts.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Quark-gluon discrimination in the search for gluino pair production at the LHC

Here, we study the impact of including quark- and gluon-initiated jet discrimination in the search for strongly interacting supersymmetric particles at the LHC. Taking the example of gluino pair production, considerable improvement is observed in the LHC search reach on including the jet substructure observables to the standard kinematic variables within a multivariate analysis. In particular, quark and gluon jet separation has higher impact in the region of intermediate mass-gap between the gluino and the lightest neutralino, as the difference between the signal and the standard model background kinematic distributions is reduced in this region. We also compare the predictions from different Monte Carlo event generators to estimate the uncertainty originating from the modelling of the parton shower and hadronization processes.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Probing gluon saturation with next-to-leading order photon production at central rapidities in proton-nucleus collisions

Here, we compute the cross section for photons emitted from sea quarks in proton-nucleus collisions at collider energies. The computation is performed within the dilute-dense kinematics of the Color Glass Condensate (CGC) effective field theory. Albeit the result obtained is formally at next-to-leading order in the CGC power counting, it provides the dominant contribution for central rapidities. We observe that the inclusive photon cross section is proportional to all-twist Wilson line correlators in the nucleus. These correlators also appear in quark-pair production; unlike the latter, photon production is insensitive to hadronization uncertainties and therefore more sensitive to multi-parton correlations in the gluon saturation regime of QCD. We demonstrate that k ⊥ and collinear factorized expressions for inclusive photon production are obtained as leading twist approximations to our result. In particular, the collinearly factorized expression is directly sensitive to the nuclear gluon distribution at small x. Other results of interest include the realization of the Low-Burnett-Kroll soft photon theorem in the CGC framework and a comparative study of how the photon amplitude is obtained in Lorenz and light-cone gauges.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2019

Gluon fragmentation into quarkonium at next-to-leading order using FKS subtraction

We present the calculation at next-to-leading order (NLO) in a s of the fragmentation function of a gluon into heavy quarkonium in the color-octet spin-singlet S-wave channel. To calculate the real NLO corrections, we adapt a subtraction scheme introduced by Frixione, Kunszt, and Signer. Ultraviolet and infrared divergences in the real NLO corrections are calculated analytically by evaluating the phase-space integrals of the subtraction terms using dimensional regularization. The subtracted phase-space integrals are then evaluated in 4 space-time dimensions. The divergences in the virtual NLO corrections are also calculated analytically. After renormalization, all the divergences cancel. The NLO corrections significantly increase the fragmentation probability for a gluon into the spin-singlet quarkonium states η c and η b .

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

Polarized gluon pseudodistributions at short distances

We formulate the basic points of the pseudo-PDF approach to the lattice calculation of polarized gluon PDFs. We present the results of our calculations of the one-loop corrections for the bilocal G μα (z)G~ λβ (0) correlator of gluonic fields. Expressions are given for a general situation when all four indices are arbitrary, and also for specific combinations of indices corresponding to three matrix elements that contain the twist-2 invariant amplitude related to the polarized PDF. We study the evolution properties of these matrix elements, and derive matching relations between Euclidean and light-cone Ioffe-time distributions. These relations are necessary for extraction of the polarized gluon distributions from the lattice data.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Coherent gluon radiation: beyond leading-log accuracy

Abstract Results are presented for the medium-induced, soft coherent radiation spectrum for all 2 → 2 partonic channels in QCD, at leading-order inα s but beyond leading logarithmic accuracy. The general formula is valid in the full kinematic range of the underlying process, and reduces to previous results in special cases. The soft gluon radiation spectrum is expressed in terms of thecolor density matrixspecific to each channel, quantifying the entanglement between the color components of the 2 → 2 production amplitude. Beyond the leading logarithm, the spectrum depends explicitly on the off-diagonal elements of this matrix, owing to the soft gluon’s ability to probe the internal color structure of the parton pair.

Physics↗
DOE OSTI2018

The seven-gluon amplitude in multi-Regge kinematics beyond leading logarithmic accuracy

We present an all-loop dispersion integral, well-defined to arbitrary logarithmic accuracy, describing the multi-Regge limit of the 2 → 5 amplitude in planar N = 4 super Yang-Mills theory. It follows from factorization, dual conformal symmetry and consistency with soft limits, and specifically holds in the region where the energies of all produced particles have been analytically continued. After promoting the known symbol of the 2-loop N -particle MHV amplitude in this region to a function, we specialize to N = 7, and extract from it the next-to-leading order (NLO) correction to the BFKL central emission vertex, namely the building block of the dispersion integral that had not yet appeared in the well-studied six-gluon case. As an application of our results, we explicitly compute the seven-gluon amplitude at next-to-leading logarithmic accuracy through 5 loops for the MHV case, and through 3 and 4 loops for the two independent NMHV helicity configurations, respectively.

1/N expansion↗
DOE OSTI2020

Medium-induced gluon radiation with full resummation of multiple scatterings for realistic parton-medium interactions

The new precision era of jet quenching observables at both RHIC and the LHC calls for an improved and more precise description of in-medium gluon emissions. The development of new theoretical tools and analytical calculations to tackle this challenge has been hampered by the inability to include the effects of multiple scatterings with the medium using a realistic model for the parton-medium interactions. In this paper, we show how the analytical expressions for the full in-medium spectrum, including the resummation of all multiple scatterings, can be written in a form where the numerical evaluation can be easily performed without the need of the usually employed harmonic or single hard approximations. We present the transverse momentum and energy-dependent medium- induced gluon emission distributions for known realistic interaction models to illustrate how our framework can be applied beyond the limited kinematic regions of previous calculations.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗