Gluons In Nuclei Research Articles

Universality test of short range nucleon-nucleon correlations in nuclei with strange and charmed probes

Understanding the EMC effect and its relation to the short-range nucleon-nucleon correlations (SRC) in nuclei is a major challenge for modern nuclear physics. One of the key aspects of the connection between these phenomena is the universality. The universality states that the SRC is responsible for the EMC effect and that the modification of the partonic structure of the SRC is the same in different nuclei. The flavor dependence of the universality is one of the unanswered questions. The investigations conducted to date have demonstrated the existence and universality of the SRC for light and quarks. Recently, it was suggested that the universality for heavy flavors can be studied through their deep subthreshold production in and eA collisions. In this paper, we discuss an alternative possibility to access the strange and gluon high-X structure of the SRC and to establish universality for heavy flavors using nuclear semi-inclusive deep inelastic scattering (nSIDIS), which probes different quark flavor combinations depending on the final state hadron. The specific reaction can be "tagged" by observation of a strange or charmed particle registered in coincidence with the scattering lepton. The universality of the SRC can be tested in the kinematic region, i.e., , where the contribution to the cross section from SRC becomes dominant. Exploring the strangeness, charmonium, and open charm will shed light on the role of quarks and gluons in nuclei, thereby developing an understanding of how nuclei emerge within QCD.

TMDs and GPDs at a future Electron-Ion Collider

In the U.S., an Electron-Ion Collider (EIC) of energy $ \sqrt{s}=20$ -100 GeV is under design, with two options studied at Brookhaven National Lab and Jefferson Laboratory. The recent 2015 US Nuclear Science Long-Range Planning effort included a future EIC as a recommendation for future construction. The EIC will be unique in colliding polarised electrons off polarised protons and light nuclei, providing the spin degrees of freedom essential to pursue its physics program driven by spin structure, multi-dimensional tomographic images of protons and nuclei, and discovery of the role of collective effects of gluons in nuclei. The foreseen luminosity of the EIC, coupled with its energy variability and reach, will allow unprecedented three-dimensional imaging of the gluon and sea quark distributions, via both TMDs and GPDs, and to explore correlations amongst them. Its hermetic detection capability of correlated fragments promises to similarly allow for precise tomographic images of the quark-gluon landscape in nuclei, transcending from light few-body nuclei to the heaviest nuclei, and could uncover how the TMD and GPD landscape changes when gluons display an anticipated collective behavior at the higher energies.

Exclusive diffractive processes in electron-ion collisions

We present a new technique to calculate the cross-section for diffractive vector meson production and DVCS in electron-ion collisions based on the dipole model. The measurement of these processes can provide valuable information on non-linear QCD phenomena, such as gluon saturation, and is the the only known way to gain insight into the spatial distribution of gluons in nuclei. We present predictions of differential cross-section distribution $d\sigma/dQ^2$ and $d\sigma/dt$ for $J/\psi$ and $\phi$ meson production for diffractive processes of heavy nuclei and demonstrate the feasibility of extracting the gluon source distribution of heavy nuclei, F(b), from coherent diffraction. We briefly introduce a new event generator based on our method that can be used for studying exclusive diffractive processes at a future electron-ion collider.

Nuclear shadowing and heavy-ion collisions at high energies

Nuclear shadowing effects for quarks and gluons are calculated using information on diffractive deep inelastic scattering on a nucleon. Role of these effects in interactions of hadrons and nuclei with nuclei at high energies is investigated. A decrease in particle densities for heavy-ion collisions in comparison with the Glauber model is predicted and nuclear modification factors are calculated. Distributions of gluons in nuclei are used to predict suppression of heavy quarkonia. The parameter-free calculation of J/ψ in DAu and AuAu collisions is in a good agreement with recent RHIC data. Predictions for heavy quarkonia suppression in heavy-ion collisions at LHC are formulated.

Coherent [formula omitted] production—A novel feature at LHC?

Energy dependence of heavy quarkonia production in hadron–nucleus collisions is studied in the framework of the Glauber–Gribov theory. We emphasize a change in the space–time picture of heavy-quark state production on nuclei with energy. Longitudinally ordered scattering of a heavy-quark system takes place at low energies, while with increasing energy it transforms to a coherent scattering of projectile partons on the nuclear target. The characteristic energy scale for this transition depends on masses and rapidities of produced particles. For J/ψ, produced in the central rapidity region, the transition happens at RHIC energies. The parameter-free calculation of J/ψ in dAu collisions is in good agreement with recent RHIC data. We use distributions of gluons in nuclei to predict suppression of heavy quarkonia at LHC.

Effects of a dynamical role for exchanged quarks and nuclear gluons in nuclei: multinucleon correlations in deep-inelastic lepton scattering

It is shown that new data from the HERMES collaboration, as well as all of the earlier improved data from experiments concerning the EMC effect and shadowing in deep-inelastic scattering of leptons from nuclei, provide strong evidence for an explicit dynamical role played by exchanged quarks and nuclear gluons in the basic, tightly-bound systems of three and four nucleons, 3 He and 4 He . This opens the way for specific quark-gluon dynamics instigating multinucleon correlations in nuclei.

Real-time evolution of soft QCD in ultra-relativistic heavy-ion collisions

The coherent wave functions of the valence quarks and gluons in nuclei, colliding at RHIC energies are represented by a coupled system of colored particles and Yang-Mills fields on the Hamiltonian gauge lattice. Coherent configurations of randomly color polarized particle and field distributions are generated and propagated on the lattice into the collision. These numerical simulations reveal interesting features for the gluon mean-field dynamics.

Gluons in nuclei and pions

The possibility of connecting apparently different descriptions of quarks in nuclei has already been shown. We now pursue the consequences of this “duality” for flavour-singlet distributions. An interesting possibility is that nuclear pions may have unusual quark-gluon substructure. Indeed, pions in general could be relatively “rich” in glue.

Muon-nucleus physics

High energy muon scattering experiments are an unique tool to study the quark gluon structure of nucleons and to investigate the role of quarks and gluons in nuclei. In this contribution, future experiments to measure the x and Q 2 dependence of the neutron structure function F 2 n and related quantities are discussed and a possible measurement of the spin dependent neutron structure function g 1 n. Some aspects of the experimental status of the EMC effect and its relevance to understand nuclear forces on a fundamental level are discussed with special emphasis to open and controversal questions which are the basis for an extensive muon nucleus physics programme to be performed during the following years at CERN and possibly at a future medium energy facility like EHF. The properties of a proposed 20 GeV muon beam at this machine are presented.