Parton Distribution Function and Orbital Angular Momentum

Grants and Contracts Details


Nucleons are the fundamental building blocks of all atomic nuclei and make up essentially all the visible matter in the universe, including the stars, the planets, and us. Our contemporary understanding of the strong interaction is based on Quantum Chromodynamics (QCD) and in this theory, the nucleon arises as a strongly interacting, relativistic bound state of quarks and gluons (referred to as partons). The nucleon is not static, but has complex internal structure, full of features that ultimately emerge from QCD dynamics and that are only now beginning to be revealed in modern experiments. Explaining the origin, the evolution, and the structure of the visible world is a central goal of nuclear physics. In order to do this, it is vital to understand the internal structure of the nucleon in terms of its partonic constituents. Over the last 50 years since the first deep inelastic scattering experiments, there have been many advances in our understanding of the partonic structure of the nucleon, including its momentum and spin structure. However there are still many puzzles and unknown aspects. With the running of the COMPASS experiment at CERN, RHIC at BNL, the E906/SeaQuest Drell-Yan experiment at Fermilab, annihilation experiments at Belle and BaBar, and experiments at JLab, we have uncovered the first layers of transverse partonic structure of the proton. The continuation of these experiments, and the future programs at JLab12, the proposed Electron-Ion Collider in the US, and at other facilities worldwide, will provide important opportunities to explore further the internal landscape of the nucleon experimentally. The results obtained in these investigations will be of increasing precision and variety; in order for these results to have optimal impact, a coordinated theoretical approach to their analysis and interpretation is required, ultimately sharpening our QCD picture of the nucleon. We have formed the TMD Collaboration to address the theoretical aspects of the question: What is the internal landscape of the nucleon? This is one of the overarching questions that serves to define the QCD frontier, one of the three scientific thrusts of the DOE's Nuclear Physics program, as described in the NSAC 2007 Long Range Plan. Owing to color confinement, the exploration of the internal landscape of the nucleons, without observing quarks and gluons directly in our detectors, is a great intellectual challenge and requires a precise matching between the cross sections of hadrons and probes of quarks and gluons. Developing such a matching necessarily requires expertise from diverse components of the Nuclear Theory subprogram. Through a Topical Collaboration, we would pull together leading nuclear theorists in QCD theory (factorization and precision of the probes), phenomenology (global analysis of data in connection with theory) and lattice QCD calculations (necessary for the non-perturbative component of the matching and first principles predictions). Our proposed Topical Collaboration would leverage the resources of the individual research groups that are involved, and would provide expanded training and opportunities for the next generation of nuclear theorists. The TMD Collaboration has a sharply focused research objective developing a precise and reliable matching between the cross sections of hadrons and the three-dimensional (3D) confined motion of quarks and gluons, the momentum-space landscape of the nucleon. Our program will directly address an important milestone set forth by the Office of Nuclear Physics long-term performance measures in high-energy nuclear physics: 2015 - Test unique QCD predictions for relations between single-transverse spin phenomena in pp scattering and those observed in deep-inelastic lepton scattering (HP13). The TMD Collaboration is committed to providing the best training for young nuclear theorists and to establishing additional permanent positions in nuclear theory. We have identified several possible bridged faculty positions from our participating institutions, and propose to use the TMD Collaboration to focus the training of postdocs and graduate students, as well as undergraduate students through summer.
Effective start/end date7/11/166/10/18


  • Brookhaven National Laboratory: $130,000.00


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