JEFFERSON LAB SEARCH

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  • Using tools that enable nuclear physics research into the heart of matter, scientists created a material for applications from aerospace to solar panels.

    The Science

  • Understanding how the structure of hadrons emerges from QCD is one of the central challenges of contemporary nuclear physics. Recent advances in lattice field theory, developments in computer technology and investment in computer resources for fundamental QCD research have now made lattice QCD a powerful quantitative tool that provides an unprecedented opportunity to understand the phenomena arising from QCD from first principles, and to make precision calculations of the predictions of QCD.

  • Hall D of the 12 GeV upgraded CEBAF will house the GlueX experiment, which intends to map the spectrum of mesons, the hybrid mesons in particular, through photoproduction off protons. Knowledge of the spectrum of hybrid mesons will aid us in understanding the nature of the confinement of quarks within hadrons, since within hybrids the gluonic field binding the meson is excited. Just as the excited states of hydrogen taught us about QED, we hope the excited states of glue in mesons will teach us about the non-trivial aspects of QCD.

  • The ratio of the electric to magnetic proton form factors has traditionally been determined using the "Rosenbluth" or longitudinal-transverse (LT) separation method, in which the ratio is extracted from the angular dependence of the cross section at fixed momentum transfer, Q2. Recent measurements at JLab using the alternative, polarization transfer (PT) technique have found a dramatically different behavior of the ratio compared with the Rosenbluth results, leading to much discussion about the possible origin of the discrepancy.

  • One of the fundamental goals of nuclear physics is to understand the structure and behavior of strongly interacting matter in terms of its basic constituents, quarks and gluons. An important step towards this goal is the characterization of the internal structure of the nucleon; the elastic electric and magnetic form factors of the proton and neutron are key ingredients of this characterization. The elastic electromagnetic form factors are directly related to the charge and current distributions inside the nucleon; these form factors are among the most basic observables of the nucleon.

  • An important goal of Jefferson Lab is to provide a detailed, three-dimensional picture of the nucleon in terms of its quark and gluon constituents, and to understand how this complex structure leads to its well known properties such as mass, spin and magnetic moment. A promising theoretical framework for this task is provided by generalized parton distributions (GPDs), which are hybrids of the usual form factors and parton distributions, but in addition include correlations between states of different longitudinal and transverse momenta.

  • The Electroweak Standard Model (SM) has to date been enormously successful. The search for a fundamental description of nature which goes beyond the SM is driven by two complementary experimental strategies. The first is to build increasingly energetic colliders, such as the Large Hadron Collider (LHC) at CERN, to excite matter into a new form.

  • Protons and neutrons are complex bound states of quarks and gluons, held together by the strong interactions of quantum chromo dynamics (QCD). Their structure may be modified inside of the dense environment of a nucleus, and such modification of hadron properties in the nuclear environment is of fundamental importance in understanding QCD. Measurements of deep inelastic scattering in nuclei show that the quark distributions in heavy nuclei are not simply the sum of the quark distributions of the constituent protons and neutron, as one might expect for a weakly bound system.

  • One of the many success stories of JLab's resonance physics program has been what we have learned about the Delta resonance, which is the lowest energy quantum excitation of the nucleon. There are several ways the nucleon can be electromagnetically excited to the Delta. One, denoted M1, or magnetic dipole moment, gives us information about the distribution of the quarks' electric current within the nucleon and Delta. Another, denoted E2, or electric quadrupole moment, describes the deviation from sphericity of the quarks' electric charge distribution.

  • The newly upgraded Jefferson Lab CEBAF Accelerator opens door to strong force studies.

    The Science

    Scientists have been rigorously commissioning the experimental equipment to prepare for a new era of nuclear physics experiments at the newly upgraded Continuous Electron Beam Accelerator Facility (CEBAF) at Jefferson Lab in Newport News, Va. These activities have already led to the first scientific result, which demonstrates the feasibility of detecting a potential new form of matter.

    The Impact