Literatura académica sobre el tema "TMDs de gluons"

The study of isolated heavy quarkonia, such as [Formula: see text] and [Formula: see text], produced in association with a photon in proton-proton collisions at the LHC, is probably the optimal way to get right away a first experimental determination of two gluon transverse-momentum-dependent distribution (TMDs) in an unpolarized proton, [Formula: see text] and [Formula: see text], the latter giving the distribution of linearly polarized gluons. To substantiante this, we calculate the transverse-momentum-dependent effects that arise in the process under study and discuss the feasibility of their measurements.

We report on the studies of Transverse-Momentum-Dependent distributions (TMDs) at a future fixed-target experiment –AFTER@LHC– using the [Formula: see text] or Pb ion LHC beams, which would be the most energetic fixed-target experiment ever performed. AFTER@LHC opens new domains of particle and nuclear physics by complementing collider-mode experiments, in particular those of RHIC and the EIC projects. Both with an extracted beam by a bent crystal or with an internal gas target, the luminosity achieved by AFTER@LHC surpasses that of RHIC by up to 3 orders of magnitude. With an unpolarised target, it allows for measurements of TMDs such as the Boer-Mulders quark distributions and the distribution of unpolarised and linearly polarised gluons in unpolarised protons. Using polarised targets, one can access the quark and gluon Sivers TMDs through single transverse-spin asymmetries in Drell-Yan and quarkonium production. In terms of kinematics, the fixed-target mode combined with a detector covering [Formula: see text] allows one to measure these asymmetries at large [Formula: see text] in the polarised nucleon.

The parton densities which are dependent on transverse momentum, open a way to understand better the structure of quarks and gluons in a more complete way. We are investigating a method based on the covariant quark model which enables us to extract the transverse momentum dependent (TMD) densities from the usual parton densities which are just dependent on the longitudinal momentum. In continuation, we obtain the dependence of the TMDs on binding energy and the mass of quarks. We do some calculations to obtain the TMDs in the unpolarized case while the mass and binding energy of partons are varying. Considering these effects, the results for TMDs are in good agreement with the results of the recent related models.

We review what is currently known about the gluon Sivers distribution and what are the opportunities to learn more about it. Because single transverse spin asymmetries inp↑p→πXprovide only indirect information about the gluon Sivers function through the relation with the quark-gluon and tri-gluon Qiu-Sterman functions, current data from hadronic collisions at RHIC have not yet been translated into a solid constraint on the gluon Sivers function. SIDIS data, including the COMPASS deuteron data, allow for a gluon Sivers contribution of natural size expected from largeNcarguments, which isO(1/Nc)times the nonsinglet quark Sivers contribution. Several very promising processes to measure the gluon Sivers effect directly have been suggested, which besides RHIC investigations, would strongly favor experiments at AFTER@LHC and a possible future Electron-Ion Collider. Due to the inherent process dependence of TMDs, the gluon Sivers TMD probed in the various processes are different linear combinations of two universal gluon Sivers functions that have different behavior under charge conjugation and that therefore satisfy different theoretical constraints. For this reason both hadronic and DIS type of collisions are essential in the study of the role of gluons in transversely polarized protons.

Three-dimensional tomography of hadrons can be investigated by generalized parton distributions (GPDs), transverse-momentum-dependent parton distributions (TMDs), and generalized distribution amplitudes (GDAs). The GDA studies had been only theoretical for a long time because there was no experimental measurement until recently, whereas the GPDs and TMDs have been investigated extensively by deeply vir- tual Compton scattering and semi-inclusive deep inelastic scattering. Here, we report our studies to determine pion GDAs from recent KEKB measurements on the differen- tial cross section of γ*γ → π0π0. Since an exotic-hadron pair can be produced in the final state, the GDAs can be used also for probing internal structure of exotic hadron candidates in future. The other important feature of the GDAs is that the GDAs contain information on form factors of the energy-momentum tensor for quarks and gluons, so that gravitational form factors and radii can be calculated from the determined GDAs. We show the mass (energy) and the mechanical (pressure, shear force) form factors and radii for the pion. Our analysis should be the first attempt for obtaining gravitational form factors and radii of hadrons by analysis of actual experimental measurements. We believe that a new field of gravitational physics is created from the microscopic level in terms of elementary quarks and gluons.

Single Spin Asymmetries and Transverse Momentum Dependent (TMD) distribution study has been one of the main focuses of hadron physics in recent years. The initial exploratory Semi-Inclusive Deep-Inelastic-Scattering (SIDIS) experiments with transversely polarized proton and deuteron targets from HERMES and COMPASS attracted great attention and lead to very active efforts in both experiments and theory. A SIDIS experiment on the neutron with a polarized 3 He target was performed at JLab. Recently published results as well as new preliminary results are shown. Precision TMD experiments are planned at JLab after the 12 GeV energy upgrade. Three approved experiments with a new SoLID spectrometer on both the proton and neutron will provide high precision TMD data in the valence quark region. In the long-term future, an Electron-Ion Collider (EIC) as proposed in US (MEIC@JLab and E-RHIC@BNL) will provide precision TMD data of the gluons and the sea. A new opportunity just emerged in China that a low-energy EIC (1st stage EIC@HIAF) may provide precision TMD data in the sea quark region, complementary to the proposed EIC in US.

The Electron Ion Collider (EIC) is the project for a new US-based, high-energy, high-luminosity facility, capable of a versatile range of beam energies, polarizations, and ion species. Its primary goal is to precisely image quarks and gluons and their interactions inside hadrons, in order to investigate their confined dynamics and elucidate how visible matter is made at its most fundamental level. I will introduce the main physics questions addressed by such a facility, and give some more details on the topic of Transverse Momentum Dependent parton distributions (TMDs).

The Electron Ion Collider (EIC) is the project for a new US-based, high-energy, high-luminosity facility, capable of a versatile range of beam energies, polarizations, and ion species. Its primary goal is to precisely image quarks and gluons and their interactions inside hadrons, in order to investigate their confined dynamics and elucidate how visible matter is made at its most fundamental level. I will introduce the main physics questions addressed by such a facility, and give some more details on the topic of Transverse Momentum Dependent parton distributions (TMDs).

Unpolarized protons can generate transversely polarized quarks or linearly polarized gluons through a distribution known as the Boer-Mulders’ function. The fragmentation of similarly polarized partons to unpolarized hadrons is called the Collins’ function. Both of these functions include correlations between the spin or polarization and the relative transverse momentum of the incoming parton or outgoing hadron, with respect to the parent particle. We explore the effect of including these and other TMDs on the production of high-pT (unpolarized) hadron production from (unpolarized) proton-proton scattering. The resulting initial state anisotropies, modulated with similar final state effects, may account for the observed azimuthal anisotropy of the produced high transverse momentum hadrons, without modification to the angle integrated spectra (RAA). This may be an explanation for the existence of a v2 in high-pT hadron spectra in p-A collisions without any observable nuclear modification of the spectra.

Avec le Large Hadron Collider (LHC) et les expériences à haute énergie à venir avec le Electron-Ion Collider (EIC), nous pouvons explorer la structure élémentaire des protons. Autrefois, on pensait que les protons étaient composés de trois quarks de valence (deux quarks up et un quark down), mais nous savons désormais qu'ils contiennent également des paires éphémères de quark-antiquark de tous les six types de quarks ainsi que des gluons, les médiateurs de la force nucléaire forte, décrits par la chromodynamique quantique (QCD). Pour sonder la structure interne d'un nucléon, les fonctions de distribution des partons (PDFs) quantifient la manière dont le moment est distribué parmi les partons (quarks et gluons) longitudinalement dans une réaction, tandis transverse-momentum-dependent PDFs (TMDs) ajoutent des informations sur le moment transverse. Bien que les TMDs de quarks soient de mieux en mieux comprises, nos connaissances sur les TMDs de gluons sont encore très limitées. Cette étude se concentre sur l'extraction des TMDs de gluons à travers la production de quarkonium, en particulier des mésons J/psi, au LHC et à l'EIC, puisque le quarkonium, un méson formé par une paire quark-antiquark lourde de même saveur, provient principalement des gluons partoniques. Pour étudier de tels processus, il est essentiel qu'ils puissent être factorisés. Cela signifie que la section efficace, représentant la probabilité du processus, est une convolution d'un terme QCD perturbatif, qui peut être calculé théoriquement, et de termes non perturbatifs comme les TMDs et les éléments de matrice à longue distance (LDMEs) qui décrivent la formation du quarkonium, et qui doivent être extraits par expérimentation. Pour la production de J/psi dans les collisions électron-proton, la neutralité de couleur nécessite l'émission de gluons à faible énergie. Cela introduit la fonction de forme, cruciale pour réconcilier les cadres TMD et collinéaire (en termes de PDF) dans leur régime de recouvrement. Les calculs montrent que la fonction de forme est universelle, accompagnée d'un facteur dépendant du processus, et qu'elle devrait également jouer un rôle dans la production directe de quarkonium neutre en couleur à des ordres supérieurs. Les prédictions d'une asymétrie azimutale, liée au rapport entre les TMDs des gluons polarisés linéairement et non polarisés, suggèrent des effets mesurables à l'EIC pour sonder ces TMDs et ces fonctions de forme.De plus, un nouveau facteur non perturbatif de Sudakov a été développé pour le formalisme de l'évolution des TMD, améliorant les modèles gaussiens en extrapolant le comportement perturbatif connu dans le régime non perturbatif. Bien que novateur, ce facteur reste à déterminer expérimentalement. L'utilisation de ce nouveau facteur de Sudakov a permis d'obtenir un accord avec les données récentes de sections efficaces normalisées pour la production de paires de J/psi au LHCb. Cependant, les incertitudes liées à la variation des échelles nécessitent des corrections à des ordres supérieurs. Les études futures au LHC, telles que la production de paires d'Upsilon et la production de paires de J/psi avec un proton stationnaire, pourraient révéler davantage d'informations sur les TMDs de gluons à des énergies et fractions de moment plus élevées. Pour l'EIC, des progrès ont été réalisés vers un spectre complet pour la production de J/psi, en se concentrant sur les contributions indépendantes de l'angle. Bien que les sections efficaces TMD et collinéaires suivent des lois de puissance significativement différentes dans le régime cinématique à explorer par l'EIC, nous ne trouvons aucun problème de correspondance, car les sections efficaces TMD se trouvent au-dessus des sections collinéaires dans la région où la correspondance est censée se produire
With the Large Hadron Collider (LHC) and the upcoming Electron-Ion Collider (EIC) high-energy experiments we can investigate the elementary structure of protons. In the past, protons were thought to comprise three valence quarks (two up, one down), but now we know they also contain short-lived quark-antiquark pairs of all six quark types and gluons, the mediators of the strong nuclear force, described by quantum chromodynamics (QCD). To probe the internal structure of a nucleon, parton distribution functions (PDFs) quantify how momentum is distributed among partons (quarks and gluons) longitudinally in a reaction, while transverse-momentum-dependent PDFs (TMDs) add transverse momentum information. While quark TMDs are getting better understood, our knowledge of gluon TMDs is still very limited. This study focuses on extracting gluon TMDs through quarkonium production, particularly J/psi mesons, at the LHC and EIC, since quarkonium, a meson formed by a heavy quark-antiquark pair of the same heavy flavour, mainly originates from partonic gluons. To study such processes, it is essential that they can be factorised. This means that the cross section, representing process likelihood, is a convolution of a perturbative QCD term, that can be theoretically calculated, and nonperturbative terms like the TMDs and the long-distance matrix elements (LDMEs) which describe the formation of the quarkonium, that need to be extracted from an experiment. For J/psi production in electron-proton collisions, colour neutrality requires low-energy gluon emission. This introduces the shape function, crucial for reconciling TMD and collinear frameworks (in terms of PDFs) in their overlapping regime. Calculations show the shape function is universal, while accompanied by a process-dependent factor, and it is expected to play a role in direct colour-neutral quarkonium production at higher orders as well. Predictions of an azimuthal asymmetry, linked to the ratio of linearly polarised to unpolarised gluon TMDs, suggest measurable effects at the EIC to probe these TMDs and shape functions. Additionally, a novel nonperturbative Sudakov factor was developed for the TMD evolution formalism, improving upon Gaussian models by extrapolating known perturbative behaviour into the nonperturbative regime. While innovative, this factor remains to be determined by experiment. Employing this novel Sudakov factor agreement with recent normalised cross-section data for J/psi-pair production at the LHCb is found. However, scale variation uncertainties necessitate higher-order corrections. Future LHC studies, such as Upsilon-pair production and J/psi-pair production with one stationary proton, may reveal more about gluon TMDs at higher energies and momentum fractions. For the EIC, progress was made toward a complete spectrum for J/psi production, focusing on angle-independent contributions. Although the TMD and collinear cross sections follow significantly different power laws in the kinematic regime to be probed by the EIC, we find no matching issues, because the TMD cross sections lie above the collinear ones in the region where matching is expected to occur

La factorisation dépendante de l’impulsion transverse est utilisée pour décrire les collisions hadroniques en incluant l’impulsion transverse intrinsèque des partons à l’intérieur des hadrons. Cela requiert l’usage de distributions dépendantes de l’impulsion transverse (Transverse Momentum-Dependent distributions en anglais ou TMDs). De telles distributions doivent être extraites de données expérimentales. Les TMDs de quarks sont relativement connues grâce à des processus pour lesquels de nombreuses données sont disponibles. Les TMDs de gluons restent peu connues car il n’existe pas de processus idéal pour les étudier dans les accélérateurs en fonctionnement. Le futur Electron-Ion Collider (EIC) permettra leur étude de façon beaucoup plus complète, mais sa mise en fonctionnement n’est pas prévue avant au moins 10 ans. De plus, il est important d’étudier les TMDs à l’aide de divers processus afin de tester leur universalité qui n’est pas aussi triviale que celle des distributions colinéaires.Nous proposons d’utiliser la production de paire de quarkonia pour étudier les deux TMDs de gluon accessibles dans les collisions de protons non polarisés au LHC. Les quarkonia sont des mésons, c’est-à-dire des états liés de paires quark-antiquark. Dans le cas d’un quarkonium, la paire est faite de quarks de la même saveur lourde : les charmonia combinent un charm et un anticharm, tandis que les bottomonia combinent un bottom et un antibottom. Les mésons J/psi sont des charmonia de spin 1 et sont produits en grandes quantités au LHC. Les paires de J/psi sont en grande majorité produites via des fusions de gluons, ce qui est important pour l’étude spécifique des TMDs de gluons. L’étude d’états finaux à deux particules permet également de sélectionner diverses valeurs de l’échelle dure du processus, qui dans ce cas est de l'ordre de la masse de la paire, ce qui permet de plus d’étudier l’évolution des TMDs.Nous utilisons d’abord un modèle simple de TMDs gaussiennes pour calculer des observables de la production de paires de J/psi qui sont sensibles au TMDs. Ces observables sont le spectre de l’impulsion transverse de la paire, principalement sensible à la TMD de gluon non polarisés, et les asymétries azimutales, dont l’existence requiert la TMD de gluons linéairement polarisés. Nous utilisons également les données LHCb sur la production de paires de J/psi pour extraire l’impulsion transverse moyenne des gluons dans notre modèle gaussien. L’importante valeur obtenue est interprétée comme une conséquence de l’évolution des TMDs qui augmente l’impulsion transverse intrinsèque du gluon via des contributions perturbatives présentes aux grandes échelles dures.Nous améliorons par la suite nos prédictions en incluant l’évolution des TMDs dans le formalisme utilisé pour décrire les TMDs de gluons dans nos calculs. Dans ce modèle, la distribution des gluons non polarisés est une contribution dominante , tandis que la distribution de gluons linéairement polarisés est sous-dominante. La composante non-perturbative restante est modélisée à l’aide d’une gaussienne. Nous observons que la magnitude des asymétries calculées pour la production de paires de J/psi est plus petite que celle calculée à l’aide du modèle purement gaussien. Cependant, nous observons également que ces asymétries restent de taille raisonnable et pourraient être détectées au LHC. Nous fournissons également des prédictions pour la production de paires de Upsilon (le Upsilon est l’équivalent bottomonium du J/psi).Enfin, nous étudions la structure en termes d’hélicité de l’amplitude de production de paires de quarkonia. En effet, elle peut être décomposée en une somme de sous-amplitudes correspondant à divers états d’hélicités des gluons incidents et des quarkonia produits. Dans la limite de grande masse de la paire, ces amplitudes se simplifient grandement et expliquent comment la production de paires de J/psi optimise l’amplitude d’une asymétrie
Transverse momentum-dependent factorisation is used to describe hadronic collisions while taking into account the intrinsic transverse momentum of partons inside hadrons. This requires the use of Transverse Momentum-Dependent Parton Distribution Functions (TMDPDFs or simply TMDs) in order to parametrise the parton correlator. Such distributions need to be extracted from experimental data. Quark TMDs are relatively well known thanks to processes such as semi-inclusive deep inelastic scattering (SIDIS) and Drell-Yan for which numerous data exist. Gluon TMDs remain poorly known, since there is no ideal process to probe them in the operating colliders. The future Electron-Ion Collider (EIC) will offer a much better access to them, but its first run remains at least 10 years from now. It is also important to study TMDs in various kinds of processes in order to check their universality which is not as trivial as that of collinear PDFs.We propose to use quarkonium-pair production to study the two leading-twist gluon TMDs accessible through unpolarised proton collisions at the Large Hadron Collider (LHC). Quarkonia are mesons, i.e. bound states of a quark-antiquark pair. In the case of a quarkonium, the pair is made of heavy flavours: charmonia combine a charm with an anticharm, while bottomonia combine a bottom with an antibottom. J/psi mesons are the lowest lying vector state of charmonia and are produced in large amounts at the LHC. J/psi pairs originate from gluon fusion in vast majority, which is important in order to focus on gluon TMDs. Studying two-particle final states also allows one to tune the hard scale of the process commensurate to the pair mass, which in turn allows one to study TMD evolution.We first use a model of Gaussian-based TMDs to compute observables in J/psi-pair production that are sensitive to the TMDs. These observables are the transverse-momentum spectrum of the pair, mostly sensitive to the unpolarised gluon TMD, and azimuthal asymmetries, whose existence requires the linearly-polarised gluon TMD. We see that J/psi pair production is an ideal process to probe the linearly-polarised gluon distribution through one azimuthal asymmetry that is maximal at large hard scales. We also use the LHCb data on the J/psi pair transverse momentum to fit the average gluon transverse momentum using our Gaussian-based model. The large value that is obtained is interpreted as a consequence of TMD evolution that perturbatively enhances the intrinsic transverse momentum of the gluon at such large hard scales.We then improve our predictions by including TMD evolution in the formalism used to describe the gluon TMDs in our calculations. In this picture, the unpolarised gluon distribution is a leading contribution in an expansion of the strong coupling, while the linearly-polarised distribution is subleading. The remaining nonperturbative component is modelled using a Gaussian. We observe that the computed magnitude of the azimuthal asymmetries in J/psi-pair production are lower than when using the purely Gaussian model. However, we observe that these asymmetries remain sizeable and could be detected at the LHC. We also provide predictions for Upsilon-pair production (the Upsilon is the bottomonium equivalent of the J/psi).We finally study the helicity structure of the quarkonium-pair production amplitude. It can be written as a sum of sub-amplitudes corresponding to various helicity states of the initial-state gluons and final-state quarkonia. In the high-mass limit of the pair, the amplitudes greatly simplify and explain how the hard-scattering coefficients of J/psi-pair production maximise the size of one azimuthal asymmetry, as previously observed. Moreover, it is shown that the amplitude zero for longitudinally polarised pairs predicted at leading order in the collinear regime exists as well in TMD factorisation. It should survive for intermediate masses as hard gluon emissions are suppressed in the TMD regime